Digital PDFs

PL-11-71-01-01-A-D

May 1971

188 pages

Original

6.2MB

Document:	PDP-11 Resource Timesharing Systm RSTS-11 BASIC-PLUS User's Guide
Order Number:	PL-11-71-01-01-A-D
Revision:	0
Pages:	188
Original Filename:	http://bitsavers.org/pdf/dec/pdp11/rsts-11/PL-11-71-01-01-A-D_RSTS-11_Users_Guide_197105.pdf

OCR Text

Resource Tirl1esharing System
RSTS-11 BASIC-PLUS
user's guide

PL-11-71-01-01-A-D

PDP - 1 1
RESOURCE TIME-SHARING SYSTEM (RSTS-ll) USER'S GUIDE

BASIC-PLUS PROGRAMMING LANGUAGE

FOR ADDITIONAL COPIES, ORDER No. PL-II-71-01-01-A-D FROM DIGITAL EQUIPMENT CORPORATION, DIRECT MAll, BUILDING 1-1, MAYNARD, MASS. 01754.

FIRST PRINTING, MAY 1971

YOUR ATTENTION IS INVITED TO THE LAST TWO PAGES OF
THIS DOCUMENT. THE READER S COMMENTS PAGE, WHEN
COMPLETED AND RETURNED, IS BENEFICIAL TO BOTH YOU
AND DEC. ALL COMMENTS RECEIVED ARE CONSIDERED. WHEN
DOCUMENTING SUBSEQUENT MANUALS. THE HOW TO OBTAIN
SOFTWARE INFORMATION PA~E OFFERS YOU A MEANS OF KEEPING UP TO DATE WITH DEC S SOFTWARE.

C:) 1971
/'~

DIGITAL

EQUIPMENT

CORPORATION

SUPPORTING AND REFERENCED DOCUMENTS:

RSTS-ll SYSTEM MANAGER'S GUIDE
(ORDER No. PL-II-71-02-01-A-D)
THESE AND OTHER DEC DOCUMENTS CAN BE ORDERED FROM
DIGITAL EQUIPMENT CORPORATION, DJRECT MAIL, BLDG.
1-1, MAYNARD, MASSACHUSETTS 017Sq
THE FOLLOWING ARE TRADEMARKS OF DIGIIA~ EQUIPMENT
CORPORATION, MAYNARD, MASSACHUSETTS Ul/Sq
DEC
FLIP CHIP
DIGITAL
OMN IBUS

PDP
FOCAL
COMPUTER LAB
UN IBUS

PREFACE
This manual contains a comprehensive description of the PDP-II
Resource Time-Sharing System, RSTS-ll.

It is organized for the bene-

fit of the beginning programmer, as i t allows the reader to gradually
acquire increased programming capabilities.
The BASIC-Plus language is an extension of BASIC
developed at Dartmouth College.

as originally

The experienced BASIC programmer may

find the appendices sufficient for his use.

However, BASIC-Plus of-

fers many features not found in standard Dartmouth BASIC or any other
version of BASIC.
BASIC-Plus incorporates the following special features:
1.

Matrix Computations, a special set of 13 commands are
available for performing matrix computations.

Alphanumeric String Capabilities, alphabetic and/or
alphanumeric strings can be manipulated with the same
ease as numeric data.
Individual characters within
these strings can be easily accessed by the user.

Program Control and Storage Facilities, facilities
are included for storing both programs and data on
any mass storage device (such as DECdisk or DECtape)
and later retrieving them for use during program execution. Programs can be entered from the RSTS terminal paper tape reader as well as from the high-speed
paper tape reader available on the computer. The
manipulation of non-disk data files is a totally new
concept in BASIC programming and will be greatly
appreciated by the more experienced BASIC programmer.
Lack of data storage facilities has always hampered
BASIC from becoming as useful a language as, for
example, FORTRAN. with this ability and the ease of
learning the BASIC language, the new user has an extremely powerful tool at his command.

Program Editing Facilities, an existing program can
be edited by adding or deleting lines, renaming the
program, or resequencing the line numbers. The user
can combine two programs into a single program, and
request the listing of a program, either in whole or
in part on his terminal or on a line printer.

Formatting of Output, controlled formatting of program
output includes facilities for tabs, spaces, and the
printing of column headings, as well as precise specification of the output line formatting.

lBASIC is a registered trademark of the Trustees of Dartmouth College.

iii

Immediate Mode of Operation, commands typed by the
user are immediately executed by BASIC-Plus instead
of being stored for later execution.

Access to System Peripheral Equipment, the user program is able to perform input and output with various
equipment, such as paper tape reader/punch, disk, DECtape, line printer, and card reader. Other peripherals
will be available on the system in the future.

Documentation and Debugging Aids, the insertion of
remarks and co~ments within a program is made somewhat more simple in this version of BASIC. Debugging
of programs is aided by the printing of meaningful
diagnostic messages which pinpoint syntactical and
other errors detected during the program execution.

A minimum RSTS-II system requires a PDP-II/20 computer, user terminals for program input and output, and a sufficient amount of program
storage area (core memory, usually
simultaneously.

20~

to accommodate several users

Mass storage devices (DECtape and DECdisk) are in-

cluded on the standard system, although additional mass storage can
be connected at a later date.

The system will support additional

core, Extended Arithmetic Element, line printer, card reader, and
high-speed reader/punch.

CONTENTS
Preface
PART I
CHAPTER 1

AN INTRODUCTION TO RSTS-ll

1.1

Introduction to Programming

1-1

1.2

The BASIC-Plus programming Language

1-2

1.3

Conventions Used in This Manual

1-2

1.4

On-Line With RSTS-ll

1-4

1.5

Special Terminal Keys

1-5

CHAPTER 2

FUNDAMENTALS OF PROGRAMMING IN BASIC-PLUS

2.1

Example BASIC Program

2-1

2.2

Line Numbers

2-1

2.3

Statements

2-3

2.3.1

Multiple Statements on a Single Line

2-3

2.3.2

A Single Statement on Multiple Lines

2-3

2.4

Character Set

2-4

2.5

Expressions

2-5

2.5.1

Numbers

2-5

2.5.2

Variables

2-7

2.5.3

Mathematical Operators

2-7

2.5.4

Relational Symbols

2-8

2.5.5

Logical Operators

2-9

CHAPTER 3

ELEMENTARY BASIC STATEMENTS

3.1

Remarks and Comments

3-1

3.2

LET Statement

3-2

3.3

programmed Input and Output

3-4

3.4

Unconditional Branch, GOTO Statement

3-6

3.5

Conditional Branch, IF-THEN and IF-GOTO Statements

3-7

3.6

Program Loops

3-11

3.6.1

FOR and NEXT Statements

3-12

3.6.2

Subscripted Variables and the DIM Statement

3-16

3.7

3-20

Mathematical Functions

3.7.1

Examples of Particular Intrinsic Functions

3-21

3.7.2

RANDOMIZE Statement

3-24

3.7.3

User Defined Functions

3-25

3.8

Subroutines

3-30

3.8.1

GOSUB Statement

3-31

3.8.2

RETURN S ta temen t

3-31

Nesting Subroutines

3.8.3

3-32

3.9

READ, DATA, and RESTORE Statements

3-33

3.10

INPUT Statement

3-35

3.11

PRINT Statement

3-37

3.11.1

Formatting Printout into Columns

3-38

3.11.2

Character Strings in PRINT Statements

3~40

3.12

STOP and END Statements

CHAPTER 4

3-42

IMMEDIATE MODE OPERATIONS

4.1

Use of Immediate Mode for Statement Execution

4-1

4.2

Program Debugging

4-1

4.3

One Statement Per Line

4-2

4.4

Restrictions an Immediate Mode

4-3

PART II
BASIC-PLUS ADVANCED FEATURES
CHAPTER 5
5.1.

CHARACTER STRINGS

Character Strings

5-1

5.1.1

Character String Names

5-2

5.1.2

Characteristics of Strings

5-2

5.2

Individual Characters within Strings, CHANGE
Statement

5-4

5.3

String Input

5-7

uu-r:pu-r:

5-9

.:n:r .Lng

5.5

String Functions

5.5.1

User Defined String Functions

CHAPTER 6

5-9
5-9

INTEGER VARIABLES AND INTEGER ARITHMETIC

6.1

Integer Variables

6-1

6.2

Integer Arithmetic

6-1

6.3

Integer I/O

6-2

6.4

User Defined Integer Functions

6-2

6.5

Use of Integers as Logical Variables

6-3

CHAPTER 7
DATA STORAGE CAPABILITIES
7.1
File Storage
7.2
OPEN Statement
Output to Various Devices
7.3
Input From Various Devices
7.4
Virtual Data Storage
7.5
CLOSE Statement
7.6
NAME-AS Statement, File Protection and Renaming
7.7
KILL Statement
7.8
CHAPTER 8
MATRIX MANIPULATION
MAT READ Statement
8.1
8.2
MAT PRINT Statement
MAT INPUT Statement
8.3
8.4
Matrix Initialization Statement
Matrix Calculations
8.5
Matrix Operations
8.5.1
8.5.2
Matrix Functions
CHAPTER 9
ADVANCED STATEMENT FEATURES
9.1
DEF Statement, Multiple Line Function Definitions
9.2
ON-GOTO Statement
9.3
ON-GOSUB Statement
9.4
ON ERROR GOTO Statement
9.5
IF-THEN-ELSE Statement
9.6
Conditional Termination of FOR Loops
9.7
Statement Modifiers
9.7.1
IF Statement Modifier
9.7.2
UNLESS Statement Modifier
9.7.3
FOR Statement Modifier
9.7.4
WHILE Statement Modifier
9.7.5
UNTIL Statement Modifier
9.8
Additional PRINT Statement Features
9.8.1
PRINT-USING Statement
9.8.2
9.9
9.10

PRINT Functions
INPUT LINE Statement
System Functions

vii

7-1
7-2
7-6

7-7
7-8
7-11
7-12
7-13

8-1
8-1
8-3
8-4
8-5
8-5
8-6

9-1
9-3
9-3
9-4
9-8
9-10
9-12
9-12
9-14
9-14
9-15
9-16
9-17
9-17
9-19
9-20
9-21

CHAPTER 10

BASIC-PLUS INPUT AND OUTPUT OPERATIONS

10.1

READ and DATA Statements

10-1

10.2

RESTORE Statement

10-2

10.3

INPUT Statement

10-2

10.4

PRINT Statement

10-5

10.5

OPEN Statement

10-9

10.6

CLOSE Statement

10-13

PART III
USING RSTS-ll
CHAPTER 11
11.1

BASIC-PLUS SYSTEM COMMANDS

ON LINE With BASIC Plus

11-1

11.1.1

Project-Programmer Numbers and Passwords

11-1

11.1.2

HELLO Command

11-1

BYE Command

11-2

11.1.3
11.2

Creating a User Program

11-3

11.3

Recalling an Old Program

11-4

11.4

Editing of User Programs

11-5

11.4.1

DELETE Command

11-6

11.4.2

LIST Command

11-7

11.4.3

CONT Command

11-8

11.5

Manipulating User Programs

11-8

11.5.1

RUN Command

11-8

11.5.2

SAVE Command

11-9

11.5.3

UNSAVE Command

11-10

..I....I...J.<t

\....n.t\..I..l'1

1.1.-1.1.

11.5.5

RENAME Command

11-12

11.5.6

REPLACE Command

11-12

11.5.7

COMPILE Command

11-12

11.6

System Status Reports

11-13

\....UllUlld.na

11.6.1

LENGTH Command

11-13

11.6.2

CATALOG Command

11-13

11.7

Using Input/Output Devices

11-14

11.7.1

TAPE Command

11-14

11.7.2

KEY Command

11-15

11.7.3

ASSIGN Command

11-15

11.7.4

DEASSIGN Command

11-16

11.8

Special Control Characters

viii

11-16

11.8.1

RETURN Key

11-16

11.8.2

ESCAPE of ALT MODE Key

11-17

11.8.3

LINE FEED Key

11-17

11.8.4

RUBOUT Key

11-17

11.8.5

CTRL/C

11-18

11.8.6

CTRL/U

11-18

11.8.7

CTRL/O

11-18

11.8.8

TAB Character

11-18

11.8.9

CTRL/P

11-19

11.8.10

CTRL/B

11-19

CTRL/Z

11-19

11.8.11

APPENDICES

BASIC-Plus Language Summary

A-I

BASIC-Plus Command Summary

B-1

BASIC-Plus Error Message Summary

C-1

ASCII Character Codes

D-1

PART I

RSTS-II AND THE BASIC LANGUAGE

This first of three parts describes the RSTS-II system,
its hardware and user features, and the simplest level of
the BASIC language.

BASIC as described in this part is

essentially Dartmouth BASIC as originally developed.
Part II describes the extended capabilities of BASIC-Plus.
As part of the introductory material, the reader will find
references to some of the extended capabilities.
As a language, BASIC is easy to learn.

BASIC-Plus

allows for capabilities to keep BASIC a useful tool for the
more sophisticated programmer.
penalize the beginning user.

BASIC does not, however,
Almost any problem can be

solved with the statements available in Part I.

The state-

ments and features in Part II allow the user to write more
efficient code and better use his time and core space.

CHAPTER 1
AN INTRODUCTION TO RSTS-ll

Although a computing system such as RSTS-ll is a complicated
arrangement of interrelated computer programs, the RSTS-ll user need
only be concerned with the writing and execution of programs in the
BASIC-Plus language.

This manual, therefore, assumes that the user

is always (and only) communicating with BASIC.

1.1

INTRODUCTION TO PROGRAMMING
For the benefit of the new programmer approaching his first com-

puting experience, there are four phases in programming a computer:
a.

writing the computer program,

entering the program to the computing system,

testing and debugging the program, and

running the finished program.

BASIC-Plus is the language in which the user writes programs
designed for the RSTS-ll system.

Input of the completed program is

generally performed from the terminal keyboard on a time-sharing system.

A program can be input through various peripheral devices, such

as the paper tape reader, magnetic tape (DECtape), or punched cards;
however, the initial creation of a BASIC program is usually performed
on-line to the computer with the terminal keyboard.
Ideally, a program runs correctly as written, but in practice
this is seldom the case.

A program can contain simple typing mistakes

or complex logical errors.

Typing and syntactical errors are detected

as the program is first typed at the keyboard and appropriate error
messages are printed.

BASIC-Plus also evaluates the entire program

for commonly made errors and generates messages which explain the
mistakes to the user.

Program errors are corrected on-line from the

terminal keyboard.
The testing and debugging process is continued until the program
appears to execute correctly.

This is a good time to explain to the

new user that a computer program only does what the programmer has
written.

The calculations performed by the computer are not necessar-

ily those that will produce the correct results.
1-1

In order to obtain

correct results from a computer, the user must write a program which
is not only free of detectable errors, but one which correctly
analyzes his problem.
RSTS-ll provides keyboard commands which enable the user not only
to create and execute his program but also to save the program within
the system for later retrieval and execution or modification.

This

saving process is known as storing or filing the program.
1.2

THE BASIC-PLUS PROGRAMMING LANGUAGE
BASIC-Plus (which is hereafter referred to simply as BASIC in

most cases) is one of the simplest of all programming languages because of its small number of powerful but self-explanatory statements
and commands and its easy application in solving problems.

Its wide

use in scientific, business, and educational installations attests to
its value and straightforward application.
BASIC is similar to many other programming languages in various
respects (and is, consequently, very easy for the experienced programmer to learn), but is especially suited for time-sharing because of
its conversational nature.

A conversational language is one which

allows the user to communicate with the language processor by typing
on the terminal keyboard.

~ASIC

responds by printing on the terminal

printer, providing for an interactive man/machine relationship.
BASIC-Plus contains both elementary statements used to write
simple programs and advanced programming techniques and statements to
write complex and efficient programs.
plex, but efficient.

The key word here is not com-

As the user progresses and gains programming

experience, he will naturally find himself becoming more efficient
and able to use the more sophisticated data manipulations.

Almost

any problem can be solved with the simple BASIC statements.

Later

in the user's programming experience, the advanced techniques can be
added.
1.3

CONVENTIONS USED IN THIS MANUAL
Certaih documentation conventions are used throughout this manual

to clarify examples of BASIC syntax.

Each BASIC statement is described

at least once in general terms using the following conventions:
a.

Angle brackets indicate essential elements of the

1-2

statement or command being described.

line number
b.

LET

For example:

= <expression>

Square brackets indicate a choice among two or more
possibilities. For example:
rTHEN <s tatemen t>
line number
IF <expression> ITHEN <line number>l
~OTO < line number~

Braces indicate optional matter or a choice among
optional elements:

line number IF <expression>

[THEN <statement> ~.fELSE
ITHEN < line number> (ELSE
:GOTO <line number>

<statement> ~
< line number>j

Items in lower case type (formulaJ variable, etc., above)
are supplied by the user according to rules explained in
the test.
Items in capital letters (LET, IF, THEN, etc.)
must appear exactly as shown because they form the BASIC
language.

The term line number used in examples (as in (c) above)
indicates that any line number is valid.

The use of some terms in this document may be unfamiliar to the
new user.

The following definitions and explanations are valid

throughout this manual:
a.

BASIC (that is, the computer) prints on the teleprinter
whereas the user types on the keyboard.

'b.

A statement is a line (or part of a line or multiple
lines in some cases, see sections 2.3.1 and 2.3.2)
within a user program containing a BASIC language
instruction. Each line is preceded by a line number.
A line is terminated by typing the RETURN key.

Commands cause BASIC to perform some operation or
task immediately and are not preceded by a line number.
Commands are always terminated with the RETURN key.

User programs consist of a series of statements
written by a person using the system in the BASIC-Plus
language.

The RSTS-ll terminal is in most cases an ASR-33
Teletype l • However, RSTS-ll can accommodate virtually
any typewriter type device. The RSTS-ll user terminal
is alternatively referred to as terminal, teleprinter,
or keyboard, depending upon what part or whether the
whole device is indicated.

ITeletype is a registered trademark of the Teletype Corporation.

1-3

1.4

ON-LINE WITH RSTS-ll
In order to use the RSTS-ll system, the user should sit down at

a terminal and turn the LINE-OFF-LOCAL knob to LINE.

The user should

then type
HELLO
followed by the RETURN key.

The system responds by skipping a line at

the terminal and printing a # character.

The user should follow this

with his project-programmer numbers (assigned by the system manager) •
The two numbers are separated by a comma and entered to the system
with the RETURN key.

The system then prints:

PASSWORD:
and waits for the user to type the password code assigned to him by
the system manager.

This code does not echo as it is typed by the

user in order to maintain the security of controlled system usage.
If the entry codes typed are acceptable to the system, the message:
WELCOME TO RSTS-ll
NEW OR OLD-is printed.

In reply, the user can indicate the creation of a NEW

program or recalling of an OLD one.

Other system commands are ex-

plained in PART III.
The entire process of preparing to enter a new program onto
the system might look as follows.

Notice that 1,2 is the project-

programmer number, the password is not echoed at the terminal, a NEW
program is to be created, and its name is MATRIX.

The system prints

READY to indicate that it is able to accept BASIC input.
HELLO
#1,2
PASSWORD:
WELCOME TO RSTS-ll
NEW OR OLD--NEW
NEW FILE NAME--MATRIX
READY

1-4

Once a program has been typed and minor typing errors corrected,
the program can be made to execute by typing RUN or RUNNH.

The RUNNH

form omits printing the name of the program and the current date before
the program output.
this data or not.

The choice belongs to the user whether he wishes
By typing LIST or LISTNH (NH stands for "no head-

ing"), the user can obtain a clean listing of the program.

These two

commands (RUN and LIST) are used frequently throughout this manual.
See Figure 2-1 for an example.
1.5

SPECIAL TERMINAL KEYS
Throughout this manual, reference is made to typing various

special keys on the RSTS-ll terminal.
not mentioned, but assumed.

In many cases, these keys are

The user will quickly learn the use of

the more important control keys on the terminal.

As an introduction,

the user is directed to consider the keys explained below.

All

special keys are described in Chapter 11.
The RETURN key causes two operations to be performed:
a.

An automatic carriage return/line feed operation is
executed. The printing head returns to the beginning
of the line (carriage return) and the paper is advanced one line (line feed).

The data preceding the typing of the RETURN key is
entered into the system for evaluation. All commands to BASIC and lines in a user program are
terminated by typing the RETURN key.

The RUBOUT key is used to correct typing mistakes.

Typing this

key once causes the last character typed to be deleted from the
terminal input buffer (remember that an entire line is entered at once
when the RETURN key is typed).

Pressing the RUBOUT key N times

causes the last N characters typed to be deleted.
The ESCAPE key (ESC or ALT MODE on different terminals) performs
the same function as the (b) description of the RETURN key.

The

ESCAPE key prints a $ character, terminates the current input line,
and does not cause a carriage return/line feed operation.
The CTRL key (or control key) is used in combination with certain
letter keys to cause BASIC to perform special operations.

These com-

binations are performed by the user holding down the CTRL key while
typing the desired letter key, then releasing both keys.

1-5

CTRL/U and

CTRL/C are examples of these combinations and how they are shown in the
test.

Some of the CTRL/key combinations are introduced below for use

when working through this manual.

All usable combinations are de-

scribed in Chapter 11.
a.

CTRL/U is used to delete an entire line up to the last
point at which the RETURN or ESCAPE key was last typed.
BASIC responds with a carriage return/line feed so
that the user can continue typing on a fresh line.

CTRL/C is used to interrupt the execution of a program
and return to the interactive BASIC processor. When
typed by the user, CTRL/C causes the system to echo
tc and when BASIC is able to accept commands, the
system prints READY.
(READY is printed instantaneously
after typing CTRL/C.)

The LINE FEED key serves as a IIlocalli RETURN key, allowing a
user to type a logical BASIC program line longer than the 72 characters
which can be typed on one line on the teleprinter.

Anything typed on

the line subsequent to the typing of the LINE FEED key is treated as
if it were part of the preceding line.
~iReo

two

01· ftlO]!l&

:l:ines

~he e~atemQat ~G ~~kQ&

ce:n"""be-"6-~··,...aft¥-~l.QA~~

For example:

REM THIS IS A PROGRAM WHICH
COMPUTES AND PRINTS THE STATISTICAL
RESULTS OF A CENSUS SURVEY

The message within the REM statement is 84 characters long, but is
spaced over three lines to make it more conspicuous.

The 91 charac-

ters in the whole REM statement would not fit on a single teleprinter
line.

Notice that the LINE FEED key does not cause a character to be

printed.

1-6

CHAPTER 2

FUNDAMENTALS OF PROGRAMMING IN BASIC-PLUS

2.1

EXAMPLE BASIC PROGRAM
The program in Figure 2.1 is an example of a user program

written in the BASIC-Plus language.

It illustrates the syntax and

elements of the language as well as standard formatting of statements
and the appearance of terminal output.
The user program (the lines numbered 10 through 200) may at this
time mean little, although the remark in the first line (line 10) and
the printed results (following the word RUN) clearly show that the
program computes interest payments.
A user program is composed of lines of statements containing
instructions to BASIC.

Each line of the program begins with a line

number that serves to identify that line as a statement and to indicate the order in which statements are to be evaluated for execution.
Each statement starts with an English word specifying the type of
operation to be performed.
2.2

LINE NUMBERS
Each line of a user program is preceded by a line number.

Line

numbers:
a.

indicate the order in which statements are normally
evaluated;

enable the normal order of evaluation to be changed;
that is, the execution of the program can branch or
loop through designated statements (this is explained
further in the sections on the GOTO, GOSUB, and
IF-THEN statements in Chapter 3); and

enhance program debugging by permitting modification
of any specified line without affecting any other
portion of the program (see section 11.4).

Line numbers are in the range 1 to 32767.

It is good programming

practice to number lines in increments of 5 or 10 when first writing
a program, to allow for insertion of forgotten or additional lines
when debugging the program.

2-1

LISTNH
1~ REMARK - THIS PROGRAM COMPUTES INTEREST PAYMENTS
2~ INPUT "INTEREST IN PERCENT";J
3~ LET J=J/1~~
4~ INPUT "AMOUNT OF LOAN"; A
5~ INPUT "NUMBER OF YEARS"; N
6~ INPUT "NUMBER OF PAYMENTS PER YEAR"; M
7~ LET N=N*M: I=J/M: B=1+1
8[1 LET R=A*I/(l-l/BtN)
9fl PRINT
1flfl PRINT" AMOUNT PER PAYMENT ="; INT(R*1flt2+.5)/1flt2
11fl PRINT "TOTAL INTEREST
="; INT((R*N-A)*1flt2+.5)/1flt2
12~ PRINT
13fl LET B=A
14fl PRINT "INTEREST
APP TO PRIN
BALANCE OF PRIN"
15fl LET L=B*I: P=R-L: B=B-P
16fl PRINT INT(L*10t2+.5)/1fl t 2, INT(P*1flt2+.5)/1flt2,
INT(B*1~t2+.5)/1flt2
17~
18~

IF B>=R GOTO 15fl
PRINT INT((B*I)*1~t2+.5)/1flt2, INT((R-B*I)*1~t2+.5)/lflt2
19f1 PRINT "LAST PAYMENT ="; INT((B*I+B)*1flt2+.5)/lflt2
2nfl END
READY
RUNNH
INTEREST IN PERCENT? 7.5
AMOUNT OF LOAN? 25flfl
NUMBER OF YEARS? 2
NUMBER OF PAYMENTS PER YEAR? 4
AMOUNT PER PAYMENT =339.44
TOTAL INTEREST
=215.51
APP TO PRIN
INTEREST
46.88
292.56
41.39
298.fl5
35.8
3fl3.64
3fl9.33
3fl·11
24.31
315.13
18.4
321.fl4
12.38
327·fl6
6.25
333.19
LAST PAYMENT =339.44

BALANCE OF PRIN
22~7.44

19/19.39
16/15.75
1296.42
981.29
66fl.25
333.19

READY

Figure

2-1

EXAMPLE BASIC PROGRAM

2-2

When the program is executed (with the use of the RUN command) ,
BASIC evaluates the statements in the order of their line numbers,
starting with the smallest line number and going to the largest
(regardless of the order in which they were typed or entered) •
2.3

STATEMENTS
Each line number is followed by an English word.

The word

identifies the type of statement and informs BASIC what to do or how
to treat the data (if any) which follows the word.
2.3.1

Multiple Statements on a Single Line
More than one statement can be written on a single line as long

as each statement (except the last) is terminated with a colon.

Thus

only the first statement on a line can (and must) have a line number.
for example:
l~

INPUT A,B,C

is a single statement line, while
2~

LET X=l:

PRINT X,Y,Z:

IF X=2 GOTO

is a mUltiple statement line containing three statements:

a LET, a

PRINT, and an IF-GOTO statement.
Any statement can be used anywhere in a multiple statement line
except as noted in the discussion of the individual statements.
2.3.2

A Single Statement on Multiple Lines
A single statement can be continued on the next line of the

program.

To indicate that a statement is to be continued, the line is

terminated with the LINE FEED key instead of the RETURN key.

The

LINE FEED performs a carriage return/line feed operation on the
terminal and the line to be continued does not contain a line number.
For example:
l~

LET W7=(W-X4*3) * (Z-A/
(A-B)-17)

where the first line was terminated with the LINE FEED key is

2-3

equivalent to:
l~

LET W7=(W-X4*3)*(Z-A/(A-B)-17)

Note that the LINE FEED key does not cause a printed character to
appear on the page.
The length of a multiple line statement is limited to 255 characterse
2.4

CHARACTER SET
User program statements are composed of individual characters.

Allowable characters come from the following character set:
A through Z
~

through 9

and the following special symbols and keys.

Function
$

Used in specifying string variables (section 5.1).

Used in specifying integer variables (section 6.1).

, "

Used to delimit string constants, i.e., text
strings (section 5.1).
"Begins comment part of a line (section 3.1).
Separates multiple statements on one line
(section 2.3.1).
Denotes a device or filename, or is used as an
output format effector (Chapter 7 and section 9.9).

Output format effector and list terminator
(section 3.11).
Output format effectorx (section 3.11).
LINE
FEED

Used to group arguments in an arithmetic
expression (section 2.5).

()

Arithmetic operators (section 2.5.3).

+ -

* /

When used at the end of a line, indicates that
the current statement is continued on the next
line (section 2.3.2).

t
2-4

Spaces can be used freely throughout the program to make statements easier to read.
IfJ LET B

For example:

Dt2+1

instead of:
l~LETB=D t2+1

Both of the above statements mean the same thing to BASIC and are
stored exactly the same within the computer when the program is
executed.
'1'A&s.J

2.5

JitL ¥«I.J~ . . \Js,J -As 1Mb '). p~n-a nSy -10 Hal.

EXPRESSIONS
An expression is a group of symbols which can be evaluated by

BASIC.

Expressions are composed of numbers, variables, functions, or

a combination of the preceding, separated by arithmetic or relational
operators.

Expressions are created by the programmer and inserted

into the standard BASIC statements in order to perform the various
operations which comprise the user program.
The following are examples of expressions acceptable to
BASIC-Plus.
4

A7* (Bt2+1)

X<Y
((A>B) OR (C=D»

AND A/B<>C/D

Not all kinds of expressions can be used in all statements, as is
explained in the sections describing the individual statements.

the following sections the reader is introduced to the elements which
compose BASIC expressions.
2.5.1

Numbers
Numbers, called numeric constants because they retain a constant

value throughout a program, can be positive or negative and can contain up to eight digits.

Numeric constants are written using decimal

notation, as follows:
2

-3.675
1234.5678
-1234567.8
-.00000078
2-5

The following are not acceptable numbers in BASIC:
14

However, BASIC can find the decimal expansion of those two mathematical
formulas as shown below:
14
3

is expressed as 14/3

;-? is expressed as SQR(7)

These formats are explained further in later sections.
The letter E allows further flexibility in number representation
If numbers were limited to eight digits, a computer would not be able
to solve many problems involving large numbers.

Consequently, rather

than saying that BASIC can only accept numbers with a maximum of
eight digits, we say that BASIC has eight digits of precision.

Larger

numbers can be written using the letter E to indicate "times ten to
the power," thus:

. .0.0.012345678

can be written in BASIC as l23.45678E-6

/-----------p12 3 4 5 6 7 89.0 .

can be written in BASIC as l2345679E 2

"'-\

-123456789.0.0.

can be written in BASIC as -1.2345679E 1.0

This E format representation of numbers is very flexible in that the
number .001 can be written as lE-3, .01E-l, 100E-5, or any number of
ways.

If more than eight digits are generated during any computation,

the result of that computation is automatically printed in E format.
(If the exponent is negative, a minus sign is printed after the Ei
if the exponent is positive, a space is printed:

lE-.04i

IE .04.)

The combination E7, however, is not a constant, but a variable.
The term lE7 is used to indicate that 1 is multiplied by 10 7 .
Numbers are specified according to the following rules:
a.

line numbers are unsigned decimal integers in the
range 1 to 32767.

2-6

2.5.2

integers are signed decimal numbers in the range
-32767 to +32767.
(When using numbers on a computer,
a comma is never used to separate the thousands
place from the hundreds place or anywhere else
within a number.)

floating point numbers have the absolute range
lE-9800<n<lE9800.
Variables

A variable is a data item whose value can be changed by the
programmer.

A numeric variable is denoted by a single letter or by a

letter followed by a single digit.

Thus BASIC interprets E8 as a

variable, along with A, X, NS,

and 01.

L~,

(Subscripted, Integer,

and character string variables are described in later sections.)
variables are assigned values by LET, INPUT, and READ statements.
The value assigned to a variable does not change until the next time
a LET, INPUT, or READ statement is encountered that contains a new
value for that variable or when the variable is incremented by a FOR
statement.

(These conditions are explained further in later sections.)

All variables are set equal to zero

(~)

before program execution.

Consequently i t is only necessary to assign a value to a variable when
an initial value other than zero is required.
2.5.3

Mathematical Operators
BASIC automatically performs the mathematical operations of

addition, subtraction, multiplication, division, and exponentiation.
Formulas to be evaluated are represented in a format similar to
standard mathematical notation.

There are five arithmetic operators

used to write such formulas; they are as follows:
Meaning

Symbol

Example

A+B

Add B to A

A-B

Subtract B from A

A*B

Multiply A by B

A/B

Divide A by B

Affl

Calculate A to the B power, AB

When more than one operation is to be performed in a single formula, as
is most often the case, rules are observed as to the precedence of
the above operators.

The arithmetic operations are performed in the

following sequence, with (a) having the highest precedence:

2-7

Any formula inside parentheses is evaluated before the
parenthesized quantity is used in further computations.
Where parentheses are nested, as follows:
(A+ (B* (Dt 2) ) )
the innermost parenthetical quantity is calculated first.

In the absence of parentheses in a formula, BASIC
performs operations as follows:
,.

4.
c.

I.J"~

WI/IIlIIJ

exponentiation
multiplication and division
addition and subtraction

In the absence of parentheses in a formula involving
more than one operation on the same level in (b)
above, the operations are performed left to right, in
the order that the formula is written. For example:
AtBtC

is evaluated as (AtB)tC

A*B/C

is evaluated as (A*B)/C

The formula (or expression)

~+B*CtD

is evaluated as follows:

first,

C is raised to the D power

second,

the result of the first operation is multiplied by B

third,

the result of the previous operation is added to A.

Parentheses are used to indicate any other order of evaluation.

For

example, if it is the product of Band C that is to be raised to the
D power, the expression would look as follows:
A+(B*C)tD
If it is desired to multiply the quantity A+B by C to the D power:
(A+B) *Ct D
The user is encouraged to use parentheses even where they are not
strictly required in order to make the formulas easier for his own
reading.

Ambiguities exist only in the programmer's mind, the com-

puter always performs the operations as explained above.
2.5.4

Relational Symbols
Relational symbols are used in IF-THEN statements (see section

3.5) where it is necessary to compare values.
are as follows:

2-8

The relational symbols

Mathematical
Symbol

BASIC
Symbol

Example
A=B

A is equal to B

A<B

A is less than B
A is less than or equal to B
A is greater than B

A<=B

A>B

A>=B

>=
<>

A<>B

A==B

2.5.5

Meaning

A is greater than or equal to B
A is not equal to B
A is approximately equal to B.
(That is, when printed, the two
quantities are equal in value.
Within the computer floating
point numbers can differ by a
miniscule amount in the last
decimal place but still be considered equal for all practical
purposes. )

Logical Operators
Logical operators are used in IF-THEN statements (see section 3.5)

where some condition is used to determine subsequent operations within
the user program.

The logical operators are as follows:

Operator

Example

NOT

NOT A

The logical negative of A.
NOT A is false.

AND

A AND B

The logical product of A and B.
If both
A and B have logical values, A AND B is
true if and only if both values are true
and false if either or both are false.

OR B

The logical sum of A and B.
If A and B
have logical values, then A OR B is true
if and only if at least one is true, and
false if both are false.

XOR

A XOR B

The loqical exclusive OR of A and B. If
both A-and B have logical values, A XOR B
is true if and only if the values differ,
and false if both values are equal.

IMP

A IMP B

The logical implication of A and B.
If A
and B have logical values, then A IMP B
is false if and only if A is false and B is
true; otherwise the value is true.

EQV

A EQV B

A is logically equivalent to B. If both
A and B have logical values, A EQV B is
true if the two values ~£fef and false if
they are-the-" same •
0', c r"_J ~

Meaning

--.

2-9

If A is true,

The following tables are called truth tables and describe graphically
the results of the above logical operations with both A and B given
for every possible combination of values.

In logical operations, the

only possible values a term can have are true and false (T and F) .

m
T

T
F

E~y

T~
T
F
XOR

T
F

ffi

T
A

THBj
F

AND

IMP

2-10

NOT

CHAPTER 3
ELEMENTARY BASIC STATEMENTS

This chapter describes the simplest forms of the more elementary
BASIC statements.

These statements are sufficient, by themselves, for

the solution of most problems.

Once these statements are mastered, the

user can investigate the more advanced applications of these statements
and the additional statements (such as automatic matrix manipulation)
explained in Part II.
The reader should understand that any problem which can be solved
with the more advanced techniques can also be solved with the simpler
statements, although the solution may not be as efficient.

BASIC is

a language in which lack of experience does not penalize the beginning
user.

As long as the user understands the details of his problem he

will be able to represent it in BASIC on a number of levels ranging
from the simple 'to the sophisticated.
3.1

REMARKS AND COMMENTS
It is often desirable to insert notes and messages within a user

program.

Such data as the name and purpose of the program, how to use

it, how certain parts of the program work, and expected results at
various points are useful things to have present in the program for
ready reference by anyone using that program.
There are two ways of inserting comments into a user program:
a.

the REMARK statement, and

use of the exclamation mark (!).

The REMARK statement must be preceded by a line number.

The word

REMARK can be abbreviated to REM for typing convenience, and the message
itself can contain any printing character on the keyboard.

BASIC com-

pletely ignores anything on a line following the letters REM.

(The

line number of a REM statement can be used in a GOTO or GOSUB statement,
see sections 3.4 and 3.8.1,as the destination of a jump in the program
execution.)

Typical REM statements are shown below:

19 REM- THIS PROGRAM COMPUTES THE
11 REM- ROOTS OF A QUADRATIC EQUATION
3-1

The exclamation mark is used to terminate the statement part of
a line and begin the comment part of the line.
125 LET A=2+4*SQR(C)
13~ PRINT A/2+1

For example:

!A SET EQUAL TO INITIAL VALUE
!PRINT SECOND CALCULATED VALUE

BASIC ignores everything on the line after encountering the exclamation mark.
Messages in REMARK statements are generally called remarks, those
after the exclamation mark, comments.

Remarks and comments are printed

when the user program is listed but do not affect program execution.
The lines below indicate three ways of putting the same remark
on two lines.

Lines

and 11 are REM statements.

Line 20 is one

REM statement broken into two lines with the LINE FEED key.

Line 30

is one comment (begun with a !) and broken into two lines with the
LINE FEED key.
l~ REM THIS PROGRAM COMPUTES THE
11 REM ROOTS OF A QUADRATIC EQUATION
2~ REM THIS PROGRAM COMPUTES THE
ROOTS OF A QUADRATIC EQUATION
3~
THIS PROGRAM COMPUTES THE
ROOTS OF A QUADRATIC EQUATION

3.2

LET STATEMENT
The LET statement assigns a numeric value to a variable.

Each

LET statement is of the form:

Zine number LET<variabZe>=<expression>
This statement does not indicate algebraic equality, but performs the
calculations within the expression (if any) and assigns the numeric
value to the indicated variable.
l~
2~

For example:

LET X=X+l
LET W2=(A4-Xt3)*(Z-A/B»

In line 10 the old value of X is increased by one and becomes the new
value of X.

In the second example, the formula on the right hand side

is evaluated and the numeric value assigned to W2.

3-2

The LET statement can be a simple numerical assignment, such as
5~

LET A5=35

or require the evaluation of a formula so long that it is continued on
the next line (see section 2.3.2).
BASIC-Plus also allows the user to completely omit the word LET
from what would ordinarily be called the LET statement.

The user may

find it easier to type:
l~

X=12*(S+7)

LET X=12*(S+7)

than

This is a convenience and does not alter the effect of the statement.
The LET statement can be used anywhere in a multiple statement
line, such as the following:
l~

X=44: Y=Xt2+Yl: B2+3.S*A
!

Expressions in a LET statement can include both integer and
floating point variables (section 2.5.2 and 6.1).
ways considered floating point values.).

(Constants are al-

Calculations involving data

of one type yield results of the same type.

If, however, one operand

is an integer variable and one is a floating point variable, the result is a floating point value.

The value resulting from the evalua-

tion of any expression is stored according to the data type to the
left of the equal sign.
l~
2~
3~

For example:

LET A=6.2
LET B%=A
PRINT A,B%

when executed, would result in the following being printed:
6.2

The LET statement also allows the user to assign a value to

3-3

multiple variables in the same statement.
l~

LET X,Y,Z

For example:

5.7

causes each of the three variables to be set equal to 5.7.
3.3

PROGRAMMED INPUT AND OUTPUT
This section gives the beginning user a preview of the techniques

used in performing BASIC program I/O (an abbreviation for the term
input/output).

The most elementary forms of the PRINT, INPUT, READ,

and DATA statements are described here so that the user is able to
conceptualize the creation of BASIC programs.
Using the LET statement, already described, and the following
executable statements, the user can easily write a viable BASIC program
of the simplest sort.

If he should want to try his program, these

simple I/O statements will provide a means of doing so and obtaining
tangible output.
These statements are described in detail at the end of this chapter and additional, more advanced, I/O techniques are described in
later chapters.
The PRINT statement is used to output program results.

The

PRINT statement has the basic form:

Zine number

fZist~
J

where the optional list can consist of messages to be printed or
numeric values, or both.
l~

Without the list, the PRINT statement

causes a carriage return/line feed to be performed at the teleprinter.
In order to print numeric values, the word PRINT is followed by the
variable or expression whose numeric value is to be printed.

The PRINT

statement, like the LET statement, can pe~forrn numeric calculations.
For example:
l~
2~

LET A=2: LET B=4
PRINT (A+B)*2

3-4

causes the number 12 to be printed when line 20 is executed.
A message can be easily output on the teleprinter by enclosing
the text to be printed in quotation marks, as follows:

7fJ PRINT "STUDENT NUMBER

";X

causes the following to be printed (where X=7744) :
STUDENT NUMBER

7744

The READ and DATA statements are used to input data to a program
during execution.

A DATA statement contains values which are assigned

to the variables within a READ statement.

When the execution of the

program encounters a READ statement of the form:

line number

READ <list>

the BASIC processor assigns to the first variable in the list the first
available value encountered in the pool of DATA statements within the
program.

The second variable is assigned the second value in the DATA

pool, and so on.

Variable names are separated by commas.

A DATA statement looks as follows:

line number

DATA <list>

DATA statements are usually grouped together toward the end of a
program.

All of the DATA statements in a given program are considered

to be one data pool from which subsequent READ statements obtain values.
(The values in the list are separated by commas.)

The DATA state-

ments are referenced in the order of their line numbers.
l~

READ A,B, C

2fJ READ D,E,F
311 READ A,B,C
4f.J DATA 1,2,3,4

5fJ DATA 5,6,7,8,9
results in the following assignments being made:

A=l]

B=2

when line IfJ is executed

C=3

3-5

For example:

D=D

when line

is executed

~7]
B=8

when line

is executed

E=5
F=

C=9
The INPUT statement allows the user to enter data to the program
from the terminal keyboard while the program is being executed.
data is typed by the user as BASIC asks for it.
l~

~or

The

example:

INPUT A,B,C

causes BASIC to pause during execution, print a question mark, and wait
for the user to type three numerical values.

The numbers must be

separated by commas and terminated with the RETURN key.

BASIC keeps

printing question marks until i t obtains the desired number of numeric
inputs from the keyboard.

For example, line

above would cause:

?
to be printed.

The user could type:

?15,24
followed by the RETURN key.

BASIC would reply:

?15,24
?
and wait for the user to enter a third value.

Any values entered

beyond the number required (three in the above case) would be ignored.
INPUT statements are used only when small amounts of data are to be
entered, or when data can only be supplied while the program is running.
3.4

UNCONDITIONAL BRANCH. GOTO STATEMENT
U~

The GO TO statement is used when it is desired

to~conditionally

transfer to some line other than the next sequential line in the
program.

In other words, a GOTO statement causes an immediate jump to

a specified line, out of the normal consecutive line number order of
execution.

The general format of the statement is as follows:

3-6

line number

GOTO <line number>

The line number to which the program jumps can be either greater than
or less than the current line number.

It is possible to jump both

forward and backward within a program.
Consider the following simple example:
l~
2~
3~
5~

LET A=2
GOTO 5~
LET A=SQR(A+l4)
PRINT A,A*A

When executed, the above lines will cause the following to be printed:

When the program encounters line 20, control transfers to line 50;
line 50 is executed, control then continues to the line following line
50.

Line 30 is never executed.

Any number of lines can be skipped in

either direction.
When written as part of a multiple statement line, GOTO must be
the last statement on the line.
ll~

For example:

LET A=ATN(B2) :PRINT A:GOTO

Any statement following the GOTO on the same line would never be
executed.
3.5

CONDITIONAL BRANCH, IF-THEN AND IF-GOTO STATEMENTS
The IF-THEN and IF-GOTO statements-are used to transfer condition-

ally from the normal consecutive order of statement numbers, depending
upon the truth of -some mathematical relation or relations.

The basic

format of the IF statement is as follows:

line number IF <condition>

The specified condition is tested.

HEN<statement> l

THEN<Zine number>t
GOTO<line number~

If the relationship is found false,

then control is transferred to the statement following the IF statement.

If the condition is true, the statement following the THEN is

3-7

is executed or control is transferred to the line number given after
THEN or GOTO.

(See also the IF-THEN-ELSE statement, section 9.5.)

tk~itl:"
The~condition

described above can be either a simple relational

expression in which two mathematical expressions are separated by a
relational operator, or the condition can be a logical expression in
which two relational expressions are separated by a logical operator.
For example:
A+2>B

is a relational expression

A>B AND B<=SQR(C)

is a logical expression

Either type of condition, when evaluated, is either true or false; no
numeric value is associated with the results of an IF statement.

The

relational and logical operators are described in sections 2.5.5 and
2.5.6 and are presented in Tables 3-1 and 3-2 for reference.
75 IF A*B>=B*(B+l) THEN LET D4=D4+1
In the above line the quantities A*B and B*(B+l) are compared.

If the

first value is greater than or equal to the second value, the variable
D4 is incremented by 1.

If B*(B+l) is greater than A*B, D4 is not

incremented and control passe's to the next line following line 75.

TABLE 3-1
RELATIONAL OPERATORS
Mathematical
Symbol

BASIC
Symbol

BASIC
Example
A

Meaning
A equals B

A < B

A is less than B

A<=B

A is less than or equal
to B

A > B

A is greater than B

A>=B

A is greater than or
equal to B

A<> B

A is not equal to B

"v'

A==B

A is approximately
equal to B

A./

3-8

TABLE 3-2
LOGICAL OPERATORS
Logical
Operator

BASIC
Example

NOT

NOT A

the logical negation of A

AND

A AND B

the logical product of A and B

A OR B

the logical sum of A and B

XOR

A XOR B

the logical exclusive OR of A and B

IMP

A IMP B

the logical implication of A and B

EQV

A EQV B

A is logically equivalent to B

Meaning

Truth Tables
of Logical Operators

ATfTTTl.

F~
OR

B
T
A

m m
F

EQV

T
NOT

XOR

When a line number follows the word THEN, the IF-THEN statement
is the same as the IF-GOTO statement.

The word THEN can be followed

by any BASIC statement, including another IF statement.
25 IF A>B THEN IF B>C THEN PRINT "A>B>C"
25 IF A>B AND B>C THEN PRINT " A>B>C"

3-9

For example:

The preceding two lines are logically equivalent and perform the
following operation:
if B is both less than A and greater than C, the message
A>B>C
is printed, otherwise the line following line 25 is executed.
In the following example, the IF-GOTO statement in line 20 is
used to limit the range of the variable A in line 10.

Execution of the

loop continues until the relationship A>4 is true, then immediately
branches to line 55 to end the program.

(A program loop is a series

of statements which are written so that when the statements have been
executed control transfers to the beginning of the statements.

This

process continues to occur until some terminal condition is reached.)
l~
2~

LET A=A+l: X=At2
IF A>4 GOTO 55
25 PRINT X
3~ PRINT "VALUE OF A IS" A
4.0' GO TO l~
55 END
when the above loop is executed, the following is printed:
1
VALUE OF A IS 1
4
VALUE OF A IS 2
9

VALUE OF A IS 3
16
VALUE OF A IS 4
(The reader is advised to execute these short example programs by
hand to follow the operation of the computer.)
In IF statements, the following priorities are associated with
each operator, in order to provide unambiguous evaluation of the
conditions

~pecified:

expressions in parentheses are evaluated first

intrinsic mathematical functions
~~b~ *,..\6
exponentiation (t)

C.'

-4.

QIidly minus ( ), that i~, a negeti we
~-¥a~F~i~a~bbi:l"ee~s:Mu~ce.ll'rl-ear!!sr--J",--/':A~;~8e.1;~Q~

3-10

Ift:unseF or

multiplication and division (* and /)

addition and subtraction (+ and -)

relational operators (=, <, <=, >, >=, ==, <»

NOT

AND

OR and XOR

IMP

EQV

Within the operators indicated in anyone group above,

operations

proceed from left to right.
Examples of IF-THEN statements follow:
l~
2~
3~
4~

IF A>B THEN l~~
!SIMPLE COMPARISON
IF A=B OR B=C THEN 2~~
IF A>B THEN A=-B
!AN ASSIGNMENT BY A LET
IF X>Y IMP Y>Z THEN PRINT "QED"

The IF

t can be

STA~EMENT

tatement

statement
be the
usi

GOTO, subseque

/xecuted.)

r- .

1+ ntb1' ~ ),llow~

3~{Cw.w.+t
~ L6~ts t-L. 44-0~
PROGRAM

3.6

We mentioned loops in the section on the IF-THEN and IF-GOTO
statement.

Programs frequently involve performing certain operations

a specific number of times.
particularly well suited.

This is a task for which a computer is
With simple tasks, such as computing a

list of prime numbers between 1 and 1,000,000, a computer can perform
the operations and obtain correct results long before the human being
attempting the same task even becomes bored.

To write a loop, the

programmer must ensure that the series of statements is repeated until
a terminal condition is met.
Programs which use loops can be illustrated by using two.versions
of a program to print a table of the positive integers 1 through 100
together with the square root of each.
program is 101 lines long and reads:

3-11

Without a loop, the first

l~
2~
3~

99~

l~~~
l~l~

PRINT 1, SQR(l)
PRINT 2, SQR(2)
PRINT 3, SQR(3)

PRINT 99, SQR(99)
PRINT l~~, SQR(l~~)
END

with the following program example, using a simple sort of loop,
the same table is obtained with fewer lines of statements:
l~
2~
3~
4~
5~

LET X=l
PRINT X,SQR(X)
LET X=X+l
IF X<=l~~ THEN
END

Statement 10 assigns a value of 1 to X, thus setting up the initial
conditions of the loop.
printed.

In line 20, both 1 and its square root are

In line 30, X is incremented by 1.

Line 40 asks whether X

is still less than or equal to 100; if so, BASIC returns to print the
next value of X and its square root.

This process is repeated until

the loop has been executed 100 times.

After the number 100 and its

square root have been printed, X becomes 101.

BASIC now receives a

negative answer to the question in line 40, does not return to line 20,
but goes to line 50 which ends the program.
All program loops have four characteristic parts:

3.6.1

initialization, the conditions which must exist for the
first execution of the loop are created (iine 10 above)

the body of the loop in which the operation which is
to be repeated is performed (line 20 above)

modification, which alters some value and makes each
execution of the loop different from the one before
and the one after (line 30 above)

terminal condition, once this exit test is satisfied
the loop is considered completed and execution continues
to the program statements following the loop (line 40
above)
FOR and NEXT Statements

The FOR statement is of the form:
line number FOR <variable>=<expression> TO <expression> STEP <expression>

3-12

For example:
l~

FOR K=2 TO

STEP 2

which causes program execution to cycle through the designated loop
using K as 2, 4, 6, 8, .•. , 20 in calculations involving K.

When K=20,

the loop is left behind and the program control goes to the line following the associated NEXT statement.
The variable in the FOR statement must be unsubscripted, although
a common use of such loops is to deal with subscripted variables using
the FOR variable as the subscript of a previously defined variable
(this is explained in further detail in section 3.6.2).

The expres-

sions in the FOR statement can be any acceptable BASIC expression as
already defined in section 2.5.
The NEXT statement signals the end of the loop which began with
the FOR statement.

The NEXT statement is of the form:

line number

NEXT <variable>

where the variable is the same variable specified in the FOR statement.

Together the FOR and NEXT statements describe the boundaries

of the program loop.

When execution encounters the NEXT statement,

the computer adds the STEP value to the variable and checks to see if
the variable is still less than the terminal value.

When the variable

exceeds the terminal value control falls through the loop to the
following statements.
If the STEP value is omitted from the FOR statement, +1 is the
assumed value.

Since +1 is a common STEP value, that portion of the

statement is frequently omitted.
The expressions within the FOR statement are evaluated once upon
initial entry to the loop.
loop.

The variable can be modified within the

When control falls through the loop, the variable value retains

the last value used within the loop.
The following is a demonstration of a simple FOR-NEXT loop.
loop is executed 10 times, the value of I is
the loop and +1 is the assumed STEP value.

3-13

The

when control leaves

FOR I = 1 TO
PRINT I
3~ NEXT I
4~ PRINT I
l~

The loop itself is lines 10 through 30.
printed when the loop is executed.

After 1=10, control passes to line

40 which causes 10 to be printed again.
l~

FOR I

The numbers 1 through 10 are
If line 10 had been:

TO 1 STEP -1

the value printed by line 40 would be 1.
l~
2~
3~

FOR I = 2 TO 44 STEP 2
LET I = 44
NEXT I

The above loop will only be executed once since the value of 1=44 has
been reached and the termination condition is satisfied.
If, however, the initial value of the variable is greater than
the terminal value, the loop will not be executed at all.

A statement

of the format:
l~

FOR I

TO 2 STEP 2

cannot be used to begin a loop, although a statement like the following will initialize execution of a loop properly:
l~

FOR I

TO 2 STEP -2

For positive STEP values, the loop is executed until the control
variable is greater than its final value.

For negative STEP values,

the loop continues until the control variable is less than its final
value.
FOR loops can be nested but not overlapped.

The depth of nesting

depends up,on the amount of user storage space available, in other
words, upon the size of the user program and the amount of core each
user has available.

Nesting is a programming technique in which one

or more loops are completely within another loop.

The field of one

loop (the numbered lines from the FOR statement to the corresponding
NEXT statement, inclusive) must not cross the field of another loop.
The following diagrams illustrate nesting procedures:
3-14

ACCEPTABLE NESTING
TECHNIQUES

UNACCEPTABLE NESTING
TECHNIQUES

Two Level Nesting

FOR
FOR
[N. EXT
[FOR
NEXT
NEXT

FOR
FOR
NEXT
NEXT

[§

Three Level Nesting

----FOR

[}

~~~T

FOR
[ NEXT

NEXT
----NEXT
An example of a nested FOR-NEXT loop is shown below:
5 DIM X(5,10)
FOR A=l TO 5
2f1 FOR B=2 TO l~ STEP 2
3~ LET X(A,B)= A+B
4~ NEXT B
5~ NEXT A
55 PRINT X
l~

Upon execution of the above statements, BASIC will print 15 when line
55 is processed.
It is possible to exit from a FOR-NEXT loop without the counter
variable reaching the termination value.

A conditional or uncondition-

al transfer can be used to leave a loop.

Control can only transfer

into a loop which had been left earlier without being completed, ensuring that the termination and STEP values are assigned.

1h"S-r'MI~"'" "",f'JI\'tl.d J..,S M~ ..I,~ fAQ.~..n .'" ~~') ~ ~1 ~'itnfliw._ ~~1'-"C. ~c·;t;.:.,
t'W\

f~\..VJrt" Wle~o~.

Both FOR and NEXT statements
statement line.

can appear anywhere in a multiple

For example:
3-15

1.0

FOR I=l TO 1.0 STEP 5: NEXT I: PRINT "I="iI

causes:
I=6
to be printed when executed.
Neither FOR nor NEXT statement can be executed conditionally in
an IF statement.
15
16

The following statements are incorrect:

IF I<>J THEN NEXT I
IF I=J THEN FOR I=l TO J

However, FOR modifiers can appear in THEN or ELSE clauses of IF statements.
75

(Modifiers are explained in section 9.8.)

For example:

IF I=l THEN PRINT Ii FOR I=l TO 5 ELSE PRINT Ii FOR I=l.0 TO 2.0

which causes
1 2 345
to be printed where I=l.

The modifier clause applies only to the

THEN or ELSE.
3.6.2

Subscripted Variables and the DIM Statement
In addition to the simple variables which were described in

Chapter 2, BASIC allows the use of subscripted variables.

Subscripted

variables provide the programmer with additional computing capabilities
for dealing with lists, tables, matrices, or any set of related
variables.

In BASIC, variables are allowed one or two subscripts.

The name of a subscripted variable is any acceptable
BASIC variable name followed by one or two integer expressions in
parentheses.

For example, a list might be described as A(I} where

I goes from 1 to 5 as shown below:
A(l}, A(2}, A(3}, A(4), A(5)
This allows the programmer to reference each of the five elements in

3-16

the list, and can be considered a one dimensional algebraic matrix as
follows:
A (1)
A (2)
A (3)
A (4)

A(S)
A two dimensional matrix B(I,J) can be defined in a similar
manner:
B(l,l), B(1,2), .•. , B(l,J), ... , B(I,J)
and graphically illustrated as follows:

B(l,l)

B(I,2)

B(1,3)

B (1, J)

B(2,1)

B(2,2)

B(2,3)

B(2,J)

B(3,1)

B(3,2)

B(3,3)

B ( 3 , J)

B(I,3)

B(I,J)

B(I,l)

Subscripts used with subscripted variables

througho.~

a program can

be explicitly stated or be any legal expression.
It is possible to use the same variable name as both a subscripted and as an unsubscripted variable.

Both A and A(I) are valid

variables and can be used in the same program.

However, BASIC will

not accept the same variable name as both a singly and a doubly
subscripted variable name in the same program.
Use of subscripted variables requires a dimension (DIM) statement to define the maximum number of elements in a matrix.

("Matrix"

is the general term used in this manual to describe all the elements
of a subscripted variable.)

The DIM statement is of the form:

3-17

line number DIM <variable (n»,<variable(n,m»,~ ..
For example:
lId' DIM X ( 5), Y ( 4 , 2), Z (lId', lId')
12 DIM I4(1~~)
Only integer constants can be used in DIM statements to define
the size of a matrix.

Any number of matrices can be defined in a

single DIM statement as long as their representations are separated
by commas.
If a subscripted variable is used without appearing previously
in a DIM statement, it is assumed to be of length 10 in each dimension.

For this reason and for reasons of good programming practice,

all matrices should be correctly dimensioned before their use in a
program.

DIM statements are usually grouped together among the first

lines of a program.
The first element of every matrix is automatically assumed to
have a subscript of zero.

Dimensioning A(6,10) sets up room for a

matrix with 7 rows and 11 columns.

This matrix can be thought of as

existing in the following form:

AO,l .

. . AO, 10

Al,l . . • Al,lO

as shown in the following program:

3-18

LISTNH
l~ REM - MATRIX CHECK PROGRAM
2~ DIM A(6,1~)
3~ FOR I=~ TO 6
4~ LET A(I,~) = I
5~ FOR J=~ TO l~
6~ LET A(~,J) = J
7~ PRINT A(I,J)i
8~ NEXT J: PRINT: NEXT I
9~ END
READY

READY

Notice that a variable has a value of zero until it is assigned a
value.
If the user wishes to conserve core space and not make use of
the extra variables set up within the matrix, he should, for
example, say DIM A(5,9) which would result in a 6 x 10 matrix which
would be referenced beginning with the A(O,O) element.
The size and number of matrices which can be defined depend
upon the amount of user storage space available.
An example of subscripted variables follows.
ly easy when using subscripted variables.

3-19

I/O is particular-

LISTNH
5 REM PROGRAM DEMONSTRATING
READING OF SUBSCRIPTED VARIABLES
1.0 DIM A ( 5), B ( 2 , 3)
15 PRINT "A(I) WHERE I=l TO 5:"
2.0 FOR I=l TO 5
25 READ A(I) :PRINT A(I);
3.0 NEXT I
35 PRINT
4.0 PRINT
45 PRINT "B(I,J) WHERE I=l TO 2"
5.0 PRINT II
AND J=l TO 3:"
55 FOR I=l TO 2
6.0 PRINT
65 FOR J=l TO 3
7.0 READ B(I,J) :PRINT B(I,J);
75 NEXT J:NEXT I
8.0 DATA 1,2,3,4,5,6,7,8
85 DATA 8,7,6,5,4,3,2,1
9.0 END
READY
RUNNH
A(I) WHERE I=l TO 5:
1 2 3 4 5
B(I,J) WHERE I=l TO 2
AND J=l TO 3:
678
876
READY
(The MAT READ statement described in Chapter 8 makes this
process much easier.)

A DIM statement can be placed anywhere in a

multiple statement line.

Integer and string variables can also

be used in matrices as described in Sections 5.1 and 6.1.
3.7

MATHEMATICAL FUNCTIONS
Within the course of a user's programming experience, he

encounters many cases where relatively common mathematical operations
are to be performed.

The results of these common operations can

often be found in volumes of mathematical tables; i.e., sine, cosine,
square root, log, etc.

Since it is this sort of operation that

computers perform with speed and accuracy, such operations are built
into BASIC.

The user need never consult tables to obtain the value

of the sine of 23

or the natural log of 144.

When such values are

to be used in an expression, the intrinsic functions, such as
SIN(23*PI/l8,0)
LOG (144)
are substituted.
3-20

The various mathematical functions available in BASIC-Plus are
detailed in Table 3.3
Table 3.3
Mathematical Functions

Function
Code
ABS (X)
SGN (X)
INT (X)
FIX (X)
COS eX)
SIN (X)
TAN (X)

A.-rN

~(X)

SQR(X)
EXP(X)
LOG (X)
LOGl,0'(X)
PI
RND(X)

Meaning
returns the absolute value of X
returns the sign function of X, a value
of 1 preceded by the sign of X, SGN(,0')=,0'
returns the greatest integer in X which
is less than or equal to X
returns the truncated value of X,
SGN(X)*INT(ABS(X»
returns the cosine of X in radians
returns the sine of X in radians
returns the tangent of X in radians
returns the arctangent of X in radians
returns the square root of X
returns the value of etX, where e=2.l4lS
returns the natural logarithm of X, log X
returns the common logarithm of X, logl~x
has a constant value of 3.1415927
returns a random number between 0 and 1
the same sequence of random numbers
is generated each time a program is
run requiring the use of the random
number generator

Most of these functions are self-explanatory.

Those which are

more complex are explained in the following section.
3.7.1

Examples of Particular Intrinsic Functions

Sign Function, SGN(X)
The sign function returns the value

1 if X is a positive

value, 0 if X is 0, and -1 if X is negative.

For example:

SGN (3.42) = 1, SGN(-42) = -1, and SGN(23-23) = O.

3-21

LISTNH
l~ REM- SGN FUNCTION EXAMPLE
2~ READ A,B
25 PRINT "A="A, "B="B
3~ PRINT "SGN(A)="SGN(A) ,"SGN(B)="SGN(B)
4~ PRINT "SGN(INT(A»="SGN(INT(A»
5~ DATA -7.32, .44
6~ END
READY

HUNNH
A=-7.32
SGN(A)=-l
SGN(INT(A»=-l

B= .44
SGN(B)=l

READY
Integer Function, INT(X)
The integer function returns the value of the greatest integer
not greater than X.

For example, INT(34.67) = 34.

INT can be used

to round numbers to the nearest integer by asking for INT(X+.5).
example, INT(34.67+.5) = 35.

For

INT can also be used to round to any

given decimal place, by asking for
INT(X*1~tD+.5)/1~tD

where D is the number of decimal places desired, as in the following
program:
LISTNH
l~ REM- INT FUNCTION EXAMPLE
2~ PRINT "NUMBER TO BE ROUNDED";
3fl INPUT A
4~ PRINT "NO. OF DECIMAL PLACES";
5fl INPUT D
6fl LET B=INT(A*lOtD+.5)/1~tD
7fl PRINT "A ROUNDED ="B
8fl GO TO 2fl
9fl END
READY
RUNNH
NUMBER TO BE ROUNDED? 55.65342
NO. OF DECIMAL PLACES? 2
A ROUNDED = 55.65
NUMBER TO BE ROUNDED? 78.375
NO. OF DECIMAL PLACES? -2
A ROUNDED = Iflll
NUMBER TO BE ROUNDED? 67.89
NO. OF DECIMAL PLACES? -1
A ROUNDED = 711
NUMBER TO BE ROUNDED? tc
READY
3-22

For negative numbers, the largest integer contained in the number
is a negative number with the same or a larger absolute value.
example:

For

INT(-23)= -23, but INT(-14.39) = -15.

Random Number Function, RND(X)
The random number function produces a random number between 0 and
1.

The numbers are reproducible in the same order for later checking

of a program.

The argument X in the RND(X) function call can be any

number, as that value is ignored and serves no function.
LISTNH
lfl REM - RANDOM NUMBER EXAMPLE
25 PRINT "RANDOM NUMBERS"
3fl FOR I=l TO 3fl
4fl PRINT RND (fl) ,
5fl NEXT I
6fl END
READY
RUNNH
RANDOM NUMBERS
.2435fl4l
.2998482
• 75255fl9
.6fl62854
.fl66l5233
.9l623fl4
.7732576
.7387181
.5744461
.527fl493
.fl9334fl3l
.5817788

.6fl75527
.8647548
.9 fl2fll16
.47299fl2
.99228fl8
• 65fl6fl97

.946681
.7319596
.1659956
.1894784
.2lfl24fl9
.6676494

.2121133
.6fl89648
.8778697
.8799586
• 33fl9l8l
.15fl4fl93

READY

In order to obtain random digits from 0 to 9, change line 40 to read:

4fl PRINT INT(lfl*RND(fl»,
and tell BASIC to run the program again.

This time the results will

look as follows:
RANDOM NUMBERS
2
2
7
6
9
~
7
7
5
5
5
$I

9
7
1
1
2
6

6
8
9
4
9
6

READY

3-23

2
6

8
8
3
1

It is possible to generate random numbers over any range.
if the range (A,B)

For example,

is desired, use:

(B-A) *RND (~) +A
to produce a random number in the range A<n<B.
3.7.2

RANDOMIZE Statement
If the random number generator is to calculate different random

numbers every time the program is run, the RANDOMIZE statement is used.
RANDOMIZE is normally placed at the beginning of a program which uses
random numbe~s (the RND function).

When executed, RANDOMIZE causes

the RND function to choose a random starting value, so that the program
run twice will give different results.
For example:
l~
2~
3~

RANDOMIZE
PRINT RND (~)
END

will print a different number each time it is run.

For this reason,

i t is a good practice to debug a program completely before inserting
the RANDOMIZE statement.
The form of the statement is as follows:

line number

RANDOMIZE

To demonstrate the effect of the RANDOMIZE statement on two runs of
the same program, we insert the RANDOMIZE statement as statement 15
in the following program:
LISTNH
15 RANDOMIZE
2~ FOR 1=1 TO 5
25 PRINT "VALUE" I
3~ NEXT I
35 END

" IS"

RND(~)

READY
RUNNH

3-24

VALUE
VALUE
VALUE
VALUE
VALUE

1 IS
2 IS
3 IS
4 IS
5 IS

.7.0.04438
.6796673
.72.09998
.284.0528
.2242288

1 IS
2 IS
3 IS
4 IS
5 IS

.59955
.34.09859
.73.09656
.3169293
.3228311

READY
RUNNH
VALUE
VALUE
VALUE
VALUE
VALUE
READY
Clearly, the output from each run is different.
3.7.3

User Defined Functions
In some programs it may be necessary to execute the same sequence

of statements or mathematical formulas in several different places.
BASIC allows the programmer to define his own functions and call these
functions in the same way he would call the square root or trig
functions.
These user defined functions consist of a function name, the
first two letters of which are FN followed by any valid variable name.
(The type of variable name used determines the type of the function.)
For example:
FNA

floating point function

FNAI

floating point function

FNA%

integer function

FNA$

string function

-,-

We define the function once ae ~fte ,~~~iRRiAg of tAB

jtc ii.&e aec.

p~e!F~t ~efOi~

The defining or DEF statement is formed as follows:

Zine number

DEF FNa(arguments)

<expression (arguments»

where a is any acceptable (one, two, or three character) variable
name.

The arguments must be the same on each side of the equal sign

3-25

and may consist of one or more dummy variables.
l~

For example:

DEF FNA(S) = St2

will cause a later statement:
2~

LET R = FNA(4)+1

to be evaluated as R=17.
The two following programs
Program #1:
LISTNH
l~ DEF FNS(A) = AtA
2~ FOR I=l TO 5
3~ PRINT I, FNS(I)
4~ NEXT I
5~ END
Program #2:
LISTNH
l~ DEF FNS(X) = xtx
2~ FOR I=l TO 5
3~ PRINT I, FNS(I)
4~ NEXT I
5~ END
cause the same output:
RUNNH
1

1
4

27
256
3125

3
4

The arguments in the DEF statement can be seen to have no significance; they are strictly dummy variables.

The function itself

can be defined in the DEF statement in terms of numbers, variables,
other functions, or mathematical expressions.
l~

DEF FNA (X)

Xt2+3*X+4

DEF FNB (X)

FNA(X)/2 + FNA(X)

DEF FNC (X)

SQR(X+4) + 1

3-26

For example:

The statement in which the user defined function appears can have
that function combined with numbers, variables, other functions, or
mathematical expressions.
4~

~I\I~

For example:

LET R = FNA(X+Y+Z)

The user defined function can be a function of from zero to

.eigfte~ariables,

as shown below:

25 DEF FNL(X,Y,Z) = SQR(Xt2 + Yt2 + Zt2)
A later statement in a program containing the above user defined
function might look like the following:
55 LET B

FNL (D, L, R)

where D, L, and R have some values in the program.
The number of arguments with which a user defined function is
called must agree with the number of arguments with which it was
defined.
When calling a user defined function, the parenthesized arguments can be any legal expression.

The value of the expression is

substituted for the function variable.
l~
2~
3~

line

For example:

DEF FNZ(X) = xt2
LET A = 2
PRINT FNZ(2+A)

will cause 16 to be printed, when executed.

The function can be called recursively, meaning that an argument
of the function can contain the function itself, as follows:
l~
2~
3~

line

DEF FNZ(X) = xt2
LET A= 2
PRINT FNZ(2+A*FNZ(2»

will cause

l~~

to be printed when executed.

FNZ(2)=4, which

is then multiplied by A to give 8, plus 2 equals 10 as the argument.
FNZ(lO) = 100.
3-27

LISTNH
1 ! MODULUS ARITHMETIC PROGRAM
5 ! FIND X MOD M
1~ DEF FNM(X,M) = X-M*INT(X/M)
15
2~ ! FIND A+B MOD M
25 DEF FNA(A,B,M) = FNM(A+B,M)
3~

35 ! FIND A*B MOD M
40 DEF FNB(A,B,M)
FNM{A*B,M)
41
45 PRINT
5~ PRINT "ADDITION AND MULTIPLICATION TABLES, MOD Mil
55 INPUT "GIVE ME AN M"iM
6~ PRINT: PRINT "ADDITION TABLES MOD "M
65 GOSUB 8~~
7~ FOR I=~ TO M-l
75 PRINT Ii" "i
8~ FOR J=~ TO M-l
85 PRINT FNA(I,J,M);
9~ NEXT J: PRINT: NEXT I
1~~ PRINT: PRINT
11~ PRINT "MULTIPLICATION TABLES MOD " M
12~ GOSUB 8~f1
13f1 FOR I=~ TO M-l
14~ PRINT I; II
II ;
15~ FOR J=~ TO M-l
16~ PRINT FNB(I,J,M);
17~ NEXT J: PRINT: NEXT I
18~ STOP
8~~ !SUBROUTINE FOLLOWS:
81~ PRINT: PRINT TAB(4);~;
82~ FOR I=1 TO M-l
83~ PRINT I;: NEXT I: PRINT
84~ FOR I=1 TO 2*M+3
85~ PRINT "_";: NEXT I: PRINT
86~ RETURN
87~ END
READY

3-28

RUNNH
ADDITION AND MULTIPLICATION TABLES, MOD M
GIVE ME AN M? 7
ADDITION TABLES MOD 7

.0 1 2 3 4 5 6

----------------.0
1
2
3
4
5
6

f1 1 2 3 4 5 6
1
2
3
4
5
6

2 3
3 4
4 5
5 6
6 f1
f1 1

4 5 6 .0
5 6 f1 1
6 .0 1 2
f1 1 2 3
1 2 3 4
2 3 4 5

MULTIPLICATION TABLES MOD 7

.0 1 2 3 4 5 6
.0.0 f1 .0 f1 .0 .0
.0 1 2 3 4 5 6
2
f1 2 4 5 1 3 5
~ 3 6 2 5 1 4
3
4
f1 4 1 5 263
5
f1 5 316 4 2
6
.0 6 5 4 321
STOP AT LINE 18.0

.0
1

READY

Figure 3-1

Modulus Arithmetic

3-29

If the same function name is defined more than once, the first
definition is used and subsequent definitions are treated as errors
and ignored.
l~
2~

DEF FNX(X) = X12
DEF FNX(X) = X+X
ILLEGAL FN REDEFINITION
3~ PRINT FNX (6)
4~ END
RUNNH
36

The function variable need not appear in the function expression
as shown below:
DEF FNA(X) = 4 + 2
LET R
FNA(l~)+l
PRINT R
END
RUNNH
7
l~
2~
3~
4~

The program in Figure 3-1 contains examples of a multi-variable
DEF statement in lines ID, 2~ and

¥.

Integer and character string functions can also be created (in
which case the variable
FNA$(X) ,FNBI%(N».
3.8

nam~

has two or three characters:

See sections 5.5 and 6.5 for details.

SUBROUTINES
When particular mathematical expressions are evaluated several

times throughout a program, the DEF statement enables the user to
write that expression only once.

The technique of looping allows the

program to do a sequence of instructions a specified number of times.
If the program should require that a sequence of instructions be
executed several times in the course of the program, this, too, is
possible.

A subroutine is a section of code performing some unusually

lengthy operation required at more than one point in the program.
Sometimes a complicated I/O operation for a volume of data, a
mathematical evaluation which is too complex for a user defined function, or any number of other processes may be best performed in a
subroutine.

3-30

3.8.1

GOSUB Statement
Subroutines are usually placed physically at the end of a

program, before DATA statements, if any, and always before the END
statement.

The program begins execution and continues until it

encounters a GOSUB statement of the form:

line number

GOSUB <line number>

where the line number after GOSUB is the first line number of the
subroutine.

Control then transfers to that line in the subroutine.

For example:
5~ GOSUB

2~~

The first line in the subroutine can be a remark or any executable
statement.
3.8.2

RETURN Statement

Having reached the line containing a GOSUB statement, control
transfers to the line indicated after GOSUB, the subroutine is
processed until the computer encounters a RETURN statement of the form:

line number

RETURN

which causes control to return to the line following the GOSUB statement.
Before transferring to the subroutine, BASIC internally records
the next line number to be processed after the GOSUB statement; the
RETURN statement is a signal to transfer control to this line.

this way, no matter how many subroutines or how many times they are
called, BASIC always knows where to go next.

Figure 3-1 and the

following program demonstrate simple subroutines:

3-31

LISTNH
1 REM - THIS PROGRAM ILLUSTRATES GOSUB AND RETURN
111 DEF FNA(X)= ABS(INT(X»
211 INPUT A,B,C
3~ GOSUB 1~11
4fl LET A=FNA(A)
5~ LET B=FNA(B)
6~ LET C=FNA(B)
7fl PRINT
Sfl GOSUB 1~~
911 STOP
11111 REM - THIS SUBROUTINE PRINTS OUT THE SOLUTIONS
1111 REM - OF THE EQUATION: AXt2 + BX + C
11
12~ PRINT "THE EQUATION IS
"A "*Xt2 +" B "*X +" C
13~ LET D= B*B - 4*A*C
14~ IF D<>11 THEN 1711
150 PRINT "ONLY ONE SOLUTION ... X =" -B/(2*A)
1611 RETURN
1711 IF D<11 THEN 2~11
lS~ PRINT "TWO SOLUTIONS ... X =";
ISS PRINT (-B+SQR(D»/(2*A) "AND X =" (-B-SQR(D»/(2*A)
19~ RETURN
21111 PRINT "IMAGINARY SOLUTIONS... X = (" ;
2115 PRINT -B/(2*A) "," SQR(-D)/(2*A) ") AND
(";
2~7 PRINT -B/(2*A) "," -SQR(-D)/(2*A) ")"
21~ RETURN
9~11 END
READY
RUNNH
? 1,.5,-.5
THE EQUATION IS
1 *Xt2 + .5 *X
TWO SOLUTIONS ... X
.5 AND X
-1

+ -.5

THE EQUATION IS
1 *Xt2 + 11 *X + 1
IMAGINARY SOLUTIONS ..• X = ( 11 , 1) AND

(11 ,-1 )

READY
Lines 100 through 210 constitute the subroutine.
is executed from line 30 and again from line SO.

The subroutine

When control returns

to line 90 the program encounters the STOP statement and terminates
execution.

Note that even though the program logically ends with a

STOP, the END statement is still present.
3.S.3

Nesting Subroutines

More than one subroutine can be used in a single program, in
which case they can be placed one after another at the end of the
program (in line number sequence).

A useful practice is to assign

distinctive line numbers to subroutines; for example, if the main
program uses line numbers up to 199, use 200 and 300 as the first
numbers of two subroutines.
3-32

Subroutines can also be nested, in terms of one subroutine calling another subroutine.

If the execution of a subroutine encounters

a RETURN statement, it will return control to the line following the
GOSUB which called that subroutine; therefore, a subroutine can call
another subroutine, even itself.

Subroutines can be entered at any

point and have more than one RETURN statement where certain conditions
will cause control to reach only one RETURN statement.

It is possible

to transfer to the beginning or any part of a subroutine; multiple
entry points and RETURNs make a subroutine more versatile.
The maximum level of GOSUB nesting is dependent on the size of
the user program and the amount of core storage available at the
particular installation.

Exceeding this limit results in the message:

MAXIMUM CORE SIZE EXCEEDED AT LINE XXX
where XXX is the line number of the line containing the error.
3.9

READ, DATA, AND RESTORE STATEMENTS
READ and DATA statements are used to enter information into the

user program during execution.

A READ statement is used to assign to

the listed variables those values which are obtained from a DATA
statement.

Neither statement is used without the other.

A READ statement is of the form:

line number

READ

<list>

A DATA statement is of the form:

line number

DATA

<list>

A READ statement causes the variables listed in it to be assigned,
in order, the next available numbers in the collection of DATA statements.

Before the program is run, BASIC takes all DATA statements in

the order they appear and creates a data block out of the numbers.
Each time a READ statement is encountered in the program, the data
block supplies the next available number or numbers.

If the data

block runs out of data, the program is assumed to be finished and an
OUT OF DATA message is printed by BASIC.

3-33

READ and DATA statements appear as follows:
l5~

READ X,Y,Z,Xl,Y2,Q9

33~

DATA 4,2,1.7

34~

DATA 6.734E-3, -174.321, 3.1415927

Note that only numbers are used in this particular DATA statement
(string data is treated in section 5.3).
Since data must be read before it can be used in a program, READ
statements normally occur near the beginning of a program.

The loca-

tion of DATA statements is arbitrary, as long as they occur in the
correct order.

A good practice is to collect all DATA statements near

the end of the program.

A DATA statement must be the only statement

on a line, while a READ statement can be placed anywhere in a multiple
statement line.
If it should become necessary to use the same data more than ·once
in a program, the RESTORE statement will make it possible to recycle
through the DATA statements beginning with the lowest numbered DATA
statement.

The RESTORE statement is of the form:

Zine number

RESTORE

For example:
85 RESTORE
will cause the next READ statement following line 85 to begin reading
data from the first DATA statement in the program, regardless of where
the last data value was found.
You may use the same variable names the second time through the
data or not, as you choose, since the values are being read as though
for the first time.
must be read.
4

In order to skip unwanted values, dummy variables

In the following example, BASIC prints:
2

on the last line because it did not skip the value for the original
N when it executed the loop beginning at line 200.

3-34

LISTNH
l~ REM PROGRAM TO ILLUSTRATE USE OF RESTORE
15 READ N: PRINT "VALUES OF X ARE: II
2~ FOR 1=1 TO N: READ X: PRINT X,
25 NEXT I
3~ RESTORE
35 PRINT: PRINT IISECOND LIST OF X VALUES II
4~ PRINT IIFOLLOWING RESTORE STATEMENT:"
45 FOR 1=1 TO N: READ X: PRINT X,
5~ NEXT I
6~ DATA 4,1,2
7~ DATA 3,4
8~ END
READY
RPNNH
VALUES OF X ARE:
1
2
3
SECOND LIST OF X VALUES
FOLLOWING RESTORE STATEMENT:
4 1 2
READY

4
3

When reading a BASIC program from the terminal tape reader, often
the last line read is the READY printed by BASIC when the program was
listed (and punched).

BASIC interprets this as a READ Y command and,

if there are no DATA statements in the program, gives
AT LINE
3.10

an "OUT OF DATA

message.

INPUT STATEMENT
The second way to input data to a program is with an INPUT state-

ment.

This statement is used when writing a program to process data

to be supplied while the program is running.

During execution, the

programmer can type values as the computer asks for them.
terminal INPUT is described in Chapter 7.)

(Non-

Depending upon how many

values are to be accepted by the INPUT command, the programmer may
wish to write himself a note reminding himself what data is to be
typed at what time (this can be done with the PRINT or INPUT statement).
In the example program following, the questions are asked at execution
time:

INTEREST IN PERCENT?, AMOUNT OF LOAN?, and NUMBER OF YEARS?

The programmer knows which value is requested and proceeds to type
and enter the appropriate value.

3-35

LISTNH
1~ REM PROGRAM TO COMPUTE INTEREST PAYMENTS
15 INPUT "INTEREST IN PERCENT"; J
2~ LET J=J/1[1~
25 INPUT "AMOUNT OF LOAN"; A
311 INPUT "NUMBER OF YEARS"; N
35 INPUT "NO. OF PAYMENTS PER YEAR"; M
4~ N=N.*M: I=J/M: B=l+I: R=A*I/(l-l/BtN)
45 PRINT: PRINT "AMOUNT PER PAYMENT ="i'R
511 PRINT "TOTAL INTEREST
=";R*N-A
55 PRINT: B=A
611 PRINT "INTEREST
APP TO PRIN
BALANCE OF PRIN"
65 L=B*I: P=R-L: B=B-P
67 PRINT L,P,B
711 IF B>=R GOTO 65
75 PRINT B*I,R-B*I
8~ PRINT "LAST PAYMENT WAS "B*I+B
85 END
READY
RUNNH
INTEREST IN PERCENT? 9
AMOUNT OF LOAN? 251111
NUMBER OF YEARS? 2
NO. OF PAYMENTS PER YEAR? 4
AMOUNT PER PAYMENT =344.96154
TOTAL INTEREST
=259.69234
INTEREST
56.25
49.75399
43.11182

APP TO PRIN
288.71154
295.2~755

3111.84972

36.32[12112

3~8.64134

29.375772

315.58577
322.68645
329.9469

22.275[192
15.~14647

BALANCE OF PRIN
2211.2885
1916.118,09
1614.2312
13115.5898
990.11,04117
667.31763

337.37[173

7.59118414
337.37[17
LAST PAYMENT WAS 344.96157
READY

The INPUT statement is of the form:

line number

INPUT <list>

For example:

1[1 INPUT A,B,C
causes the computer to pause during execution, print a question mark,

3-36

and wait for the user to type three numerical values separated by
commas.

The values typed are entered to the computer by typing the

RETURN key.
As in the program above, the question mark is grammatically useful
if a printed question is to prompt the typing of the input values.
The output for the program begins after the word RUN and includes
a verbal description of the numbers.

This verbal description on the

output is optional with the programmer, although it has a definite
advantage in ease of use and understanding.
When the correct number of variables have been typed in answer
to the printed? character, type the RETURN key to enter the values
to the computer.

If too few values are listed, the computer prints

another ? to indicate that more data is requested.

If too many values

are typed, the excess data on that line is ignored.
Messages to be printed at execution time can be inserted within
the INPUT statement itself.

The message is set off by double quotes

from the other arguments of the INPUT statement.

For example:

IJ INPUT "YOUR AGE IS"; A
is equivalent to
1,r,J PRINT "YOUR AGE IS";
2,r,J INPUT A
(For a description of the PRINT statement and the use of the semicolon and comma characters, see section 3.11.)
3.11 PRINT STATEMENT
The PRINT statement is used to output data onto the terminal
teleprinter.

The general format of the print statement is:

Zine number

fZis t ~

where the list can contain expressions, text strings, or both.
the

~~b~~

indicate, the list is optional.

3-37

Used alone, the

PRINT statement:
25 PRINT
causes a blank line to be printed on the teleprinter (a carriage
return/line feed operation is performed).
PRINT statements can be used to perform calculations and print
their results.

Any expression within the list is evaluated before a

value is printed.
l~
2~
3~

Consider the following program:

LET A=l: LET B=2: LET C=3+A
PRINT
PRINT A+B~C

When this program is executed, a carriage return/line feed is performed at the terminal (line 20) and the number 7 is printed.
The PRINT statement can be used anywhere in a multiple statement
For example:

line.

A=l: PRINT A: A=A+5: PRINT: PRINT A

would cause the following to be printed on the terminal when
executed:
1

6
Notice that the teleprinter performs a carriage return/line feed at
the end of each PRINT statement.

Thus the first PRINT statement

causes a 1 and a carriage return/line feed, the second PRINT statement
is responsible for the blank line, and the third PRINT statement
causes a 6 and another carriage return/line feed to be output.
3.11.1

Formatting Printout into Columns

BASIC considers the terminal printer to be divided into five
zones of 14 spaces each.

When an item in a PRINT statement is

followed by a comma, the next value to be printed will appear in the
next available print zone.
l~
2~

For example:

LET A=3: LET B=2
PRINT A,B,A+B,A*B,A-B,B-A
3-38

When the preceding lines are executed, the following is printed:
3

-1

Notice that the sixth element in the PRINT list is printed as

th~

first entry on a new line.
Two commas together in a PRINT statement cause a print zone to
be skipped.
l~
2~

For example:
LET A=l: LET B=2
PRINT A,B"A+B

will cause the following to be printed:
1

If the last item in a PRINT statement is followed by a comma,
the next value to be printed by a later PRINT statement will appear
in the next available print zone.

For example:

l~
2~

A=1:B=2:C=3
PRINT A,:PRINT B: PRINT C
RUNNH

3
READY

If a tighter packing of printed values is desired, the semicolon character can be used in place of the comma.

A semicolon

causes the next value to be printed ~ spaceS to the right of the

preceding printout.

A semicolon following the last item in the list

causes the next pr~nted value to appear

t'VJT)

GR@

space5 to the right of

the preceding value on the same line (provided there is room left
on the line for printing).

The following example shows the various

uses of the semicolon and comma.

3-39

LISTNH
l~ LET A=l: B=2: C=3
2~ PRINT A;B;C;
3~ PRINT A+liB+liC+l
4~ PRINT A,B, C
READY
RUNNH
1 2 323 4
1

READY

3.11.2

Character Strings in PRINT Statements

The PRINT statement can be used to print a message, either alone
or together with the evaluation and printing of numeric values.
Characters are indicated for printing by enclosing them in single or
double quotation marks (therefore each type of quotation mark can
only be printed if surrounded by the other type of quotation marx) •
For example:
LISTNH
l~ PRINT "THIS IS A TEXT STRING"
2~ PRINT '"NEVERMORE"'
READY
RUNNH
THIS IS A TEXT STRING
"NEVERMORE "
READY
As another example, consider the following line:
4~

PRINT "AVERAGE GRADE IS ";X

which prints the following (where X is equal to 83.4):
AVERAGE GRADE IS

83.4

When a character string is printed, only the characters between
the quotes appear; no leading or trailing spaces are added.

Leading

and trailing spaces can be added within the quotation marks using
the keyboard space bar; the spaces will appear in the printout
exactly as they are within the quotation marks.
When a comma separates a text string from another PRINT list

3-40

item, the item is printed at the beginning of the next available
print zone.
ignored.

Semicolons separating text strings from other items are

Thus, the previous example could be expressed as:
4.0' PRINT "AVERAGE GRADE IS " X

and the same printout would result.

A colon or semicolon appearing

as the last item of a PRINT list will always suppress the carriage
return/line feed operation.
The following example demonstrates the use of the formatting
characters (, and

with text strings.

12.0' PRINT "STUDENT NUMBER "X, "GRADE
13.0' PRINT "NO. IN CLASS = "N

"Gi"AVE.

"Ai

could cause the following to be printed (assuming calculations were
done prior to line 130):
STUDENT NUMBER 11556

GRADE

AVE.

85.4

NO. IN CLASS

The above line is exactly 72 characters long (the length of the teleprinter line).

The user is advised to limit the length of his lines

for output to 72 characters to avoid their being partially printed
on the next line.
If a PRINT statement contains a message to be printed beginning
with a quotation mark and not limited by a closing quote, the entire
statement is printed as though the quote were the last character.
For example:
1.0' PRINT "A =iX
causes
A =;X
to be printed, while (if X=3):
1.0' PRINT "A =II;X

3-41

causes

to be printed.
3.12

STOP AND END STATEMENTS
The STOP and END statements are used synonymously to terminate

program execution.

The END statement is usually the last statement

in every BASIC program.

The STOP statement can occur several times

throughout a single program with conditional jumps determining which
is the actual end of the program.

The END statement is of the form:

Zine number

END

The line number of the END statement should be the largest line
number in the program.

Any lines having line numbers greater than

that of the END statement are not executed.
NOTE
A program will execute without an END statement;
however, an error message is printed if a program
is recalled having been saved without an END
statement.
The STOP statement is of the form:

Zine number

STOP

and is the equivalent to a GOTO n, where n is the line number of the
END statement.
Execution of a STOP or END statement causes the message:
READY
to be printed by the teleprinter.

This signals that the execution

of a program has been completed.

3-42

CHAPTER 4
IMMEDIATE MODE OPERATIONS

4.1

USE OF IMMEDIATE MODE FOR STATEMENT EXECUTION
It is not always necessary to write a BASIC program to use the

RSTS-ll system.

Most of the statements discussed in this manual can

either be included in a program for later execution or be given as
commands, which are immediately executed by BASIC.

This latter

facility permits the RSTS-ll user to have an extremely powerful desk
calculator available whenever he is on-line.
BASIC-Plus distinguishes between lines entered for later execution and those entered for immediate execution solely on the presence
(or absence) of a line number.

Statements which begin with line

numbers are stored; statements without line numbers are executed
immediately upon being entered to the system.
l~

Thus the line:

PRINT "THIS IS A PDP-ll~

will produce no action at the console upon entry, while the statement:
PRINT "THIS IS A PDP-II"
THIS IS A PDP-II
READY
when entered causes the immediate output shown above.

The READY mes-

sage is then printed to indicate the system readiness for another
direct command.
4.2

PROGRAM DEBUGGING
Immediate mode operation is especially useful in two areas:

program debugging and the performance of simple calculations in situations which do not occur with sufficient frequency or with sufficient
complications to justify a complete program being written.
In order to facilitate debugging a user program, the user can
place STOP statements liberally throughout the program.

Each STOP

statement will cause the program to halt, at which time the user can
examine various data values, perhaps change them in Immediate Mode,

4-1

and then give the
CaNT
command to continue his program execution.
4.3

ONE STATEMENT PER LINE
When using

Iro~ediate

Mode, nearly all the

used to generate or print results.

st~~dard

verbs can be

In Immediate Mode, however, there

can only be one BASIC statement per line.

If a

n:n

is included in an

Immediate Mode statement, the instructions to its right are ignored.
For example:
A=l: PRINT A
will cause the variable A to be assigned the value 1, but nothing is
printed at the console.

This operation could be successfully per-

formed as follows:
A=l
READY

PRINT A
1
READY

Since multiple statement lines are ignored in Immediate Mode,
explicit FOR-NEXT loops are not possible.

The use of the FOR

modifier (and all other modifiers) is allowed.
roots can be produced as follows:
PRINT I, SQR(I) FOR I=l TO
1
2
3

1.4142136
1.7320508

2.236068
2.4494897
2.6457513
2.86284271

7
8
9

3.1622777

READY

4-2

Thus a table of square

4.4

RESTRICTIONS ON IMMEDIATE MODE
Some statements, particularly those that would cause execution

of lines within a user's stored program, are not allowed in Immediate
Mode.

These statements include:
GOTO
GOSUB
References to user defined functions

Thus the following dialog might result if the user defined a function
in his program and tried to reference it in Immediate Mode.
l~ DEF FNA(X) = Xt2 + 2*X
PRINT FNA(l)
PLEASE USE THE RUN COMMAND

! SAVED STATEMENT
! IMMEDIATE MODE

READY
Certain commanus make no logical sense when used in Immediate Mode.
When these are given, the message ILLEGAL IN IMMEDIATE MODE is given:
DEF FNA(X)
1
ILLEGAL IN IMMEDIATE MODE
READY
Commands in this category include:
DEF
DIM
DATA
FOR
RETURN
NEXT
FNEND

4-3

PART II
BASIC-PLUS ADVANCED FEATURES

This part of the manual describes the special features of
BASIC-Plus which make the language a superior tool for all manner
of data manifUlation.

Additional capabilities of the statements

previously described are included, along with new statements,
character string manipulating facilities, integer mode variables
and arithmetic, intrinsic matrix functions, disk and DECtape storage
of data files, and a complete description of all BASIC Input/Output
facilities.
In general, the new techniques presented here allow the user
to write programs which conserve core space and enhance execution
time.

With the ability to manipulate character strings, the user

can write sophisticated programs requiring the ability to handle
a wide range of data.

Formatting of output is also described to

enable the user to obtain maximum effective output.
The matrix functions allow the user to perform matrix I/O,
and the matrix operations of addition, subtraction, multiplication,
inversion, and transposition.

CHAPTER 5
CHARACTER STRINGS

5.1

CHARACTER STRINGS
The previous chapters describe the manipulation of numerical

information only; however, BASIC also processes information in the
form of character strings.

A string, in this context, is a sequence

of characters treated as a unit.

A string can be composed of alpha-

betic, numeric, or alphanumeric characters.

(An alphanumeric string

is one which contains letters, numbers, spaces, or any combination
of characters.)
Without realizing it, the reader has already encountered character strings.

Consider the following program which prints the name

of a month, given its number (the ON GOTO statement is described in
section 9.2):
LISTNH
l~ INPUT "NUMBER OF MONTH IS";N
15 IF N<l OR N>12 THEN STOP
2~ ON N GOTO 3~,35,4~,45,5~,55,6~,65,7~,75,8~,85
3Il PRINT "JANUARY": GOTO 9~
35 PRINT "FEBRUARY": GOTO 9Il
4Il PRINT "MARCH": GOTO 9Il
45 PRINT "APRIL": GO TO 9Il
5Il PRINT "MAY": GOTO 9Il
55 PRINT "JUNE": GOTO 9Il
6~ PRINT "JULY": GOTO 9Il
65 PRINT "AUGUST": GOTO 9~
7~ PRINT "SEPTEMBER": GOTO 9Il
75 PRINT "OCTOBER": GOTO 9Il
8Il PRINT "NOVEMBER": GOTO 9Il
85 PRINT "DECEMBER": GOTO 9Il
9Il END
READY
RUNNH
NUMBER OF MONTH IS? 7
JULY
READY
In Chapter 3 we saw how the INPUT and PRINT statements could be
used to print a verbal message along with the input and output of
numeric values.

These messages are actually character string con-

stants (much like the number 4 is a numeric constant).
way, there are character string variables and functions.
5-1

In a similar

5.1.1

Character String Names
Variable names can be introduced for simple strings and for both

lists and matrices composed of strings (which is to say one and two
dimensional string matrices).

Any variable name followed by a dollar

sign ($) character indicates a string variable.

For example:

A$
C7$
are simple string variables.

Any list or matrix variable name

followed by the $ character denotes the string form of that variable.
For example:
V$(n)
C$(m,n)

M2$(n)
Gl$(m,n)

where m and n indicate the position of that element of the matrix
within the whole.
The same name can be used as a numeric variable and as a string
variable in the same program with the restriction that a one and a
two dimensional matrix cannot have the same name in the same program.
For example:
A

A(n)
A$(m,n)

can all be used in the same program, but
A(n) and A(m,n)
or
A$(n) and A$(m,n)
cannot.
5.1.2

Characteristics of Strings
A character string can contain any number of characters (from

to n).

However, the LINE FEED key cannot be used to type a string

on two or more terminal lines.

Since core storage is limited,

strings can also be saved in files on the system disk (see
section 7.1).

5-2

String lists and matrices are defined with the DIM statement,
as are numerical lists and matrices.

For example:

1.0' DIM Sl$(5)
indicates that there are six strings, Sl$(.0')
can be separately accessed.

through Sl$(5), which

If a DIM statement is not used, a sub-

scripted string variable is assumed to have a dimension of 10 (11
elements).

Note that the dimension of a string matrix specifies the

number of strings and not the number of characters in anyone string.
For example, if the first statements in a program are:
1.0' FOR I = 1 TO 7
2.0' LET B$(I) = "PDP-II"
3.0' NEXT I
they would cause a list B$(n) to be created having 11 accessible
elements, B$(.0') through B$(l.0').

The elements B$(l)

through B$(7)

are set equal to "PDP-II" and the others would be null strings
(have no characters).

As a general rule, all lists and matrices

should be dimensioned to the maximum size being referenced in the
program.
Just as numbers can be used as constants as well as being
referenced by variable names, BASIC-Plus allows for character string
constants.

In line 20 above, "PDP-II" is a character string constant.

Character string constants are delimited by either single or double
quotes.

For example:
1.0'5 LET Y$ = "FILE4"
33 Bl$ = 'CAN'
~.0'
IF A$ = "YES" GOTO 25.0'

Character string constants can be used in any statement where their
use has a logical meaning.
When applied to string operands, the relational operators
indicate alphabetic sequence.

For example:

55 IF A$(I)<A$(I+l) GOTO 1.0'.0'
When line 55 is executed the following occurs:

A${I) and A${I+I) are

compared; if A$(I) occurs earlier in alphabetical order than A$(I+I),

5-3

execution continues at line 100.

Table 5-1 contains a list of

the relational operators and their string interpretations.
In any string comparison, trailing blanks are ignored.
to say "YES" is equivalent to "YES

That is

TABLE 5-1
Relational Operators Used With
String Variables

Operator

Example
B$

5.2

Meaning
The strings A$ and B$ are equivalent.

A$ < B$

The string A$ occurs before B$ in alphabetical sequence.

A$ <= B$

The string A$ is equivalent to or occurs
before B$ in alphabetical sequence.

A$ > B$

The string A$ occurs after B$ in alphabetical sequence.

A$ >= B$

The string A$ is equivalent to or occurs
after B$ in alphabetical sequence.

A$ <> B$

The strings A$ and B$ are not equivalent.

INDIVIDUAL CHARACTERS WITHIN STRINGS, CHANGE STATEMENT
Individual characters in a string can be referenced through use

of the CHANGE statement.

The CHANGE statement permits the user

program to transform (the entirety oB a character string into a list
of numeric values or a list of numeric values into a character string.
Each character in a string can be converted to its ASCII equivalent
or vice versa.

Table 5-2 describes the relationship between the ASCII

characters and their numerical values.

As an illustration, consider the following:
LISTNH
1.'J DIM X (3)
15 LET A$ = "CAT"
2~ CHANGE A$ TO X
25 PRINT X(.'J) ;X(l) ;X(2); X(3)
3~ END
READY
RUNNH
3 67 65 84

READY

5-4

TABLE 5-2
ASCII CHARACTER CODES

Character
spoc.c.
II

#
$
%
&

(
)

0
1
2
3
4
5
6
7
8
9
<

>
?

ASCII Code No.
(Decimal)

Character

32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63

A
B
C
D
E
F
G

H
I
J
K

L
M

a
P

R
S
T
U
V
W
X
y

Z
[

\
]
t
-+-

ASCII Code No.
(Decimal)
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95

Additional symbols useful on output are as follows:
LF (line feed)
10
CR (carriage return) 13
The above list is not complete; there are 128 characters
numbered 0 through 127.

5-5

X(l) through X(3) take on the ASCII values of the characters in the
string variable A$. The first element of X, X(~) becomes the numbe~
of characters present in A$.

If more characters are present in the

string variable than can be accommodated in the numeric list, the
message "SUBSCRIPT OUT OF RANGE" is printed.

The first element of

the list becomes the number of characters in the string which have
been successfully transformed into numeric values, and will be less
than or equal to the dimension of the list.
Another program performing this operation is shown below:

LISTNH
l~ DIM A (65)
15 READ A$
2~ CHANGE A$ TO A
25 FOR I=~ TO A(~)
3~ PRINT A(I) i:NEXT I
35 DATA ABCDEFGHIJKLMNOPQRSTUVWXYZ
4~ END
READY
RUNNH
26 65 66 67 68 69
88 89 9~
READY

71 72 73 74 75 76 77 78 79

81 82 83 84 85 86 87

Notice that A(~) = 26.
To change numbers into string characters, CHANGE is used as
follows:
LISTNH
l~ FOR I=~ TO 5
15 READ A(I)
2~ NEXT I
25 DATA 5,65,66,67,68,69
3~ CHANGE A TO A$
35 PRINT A$
4~ END
READY
RUNNH
ABCDB"
READY
This program prints ABCDE because the numbers 65 through 69 are
the code numbers for A through E.

Before CHANGE is used in the
5-6

matrix-to-string direction, the programmer must indicate the number of
characters in the string as the zero element of the matrix.
15 of the previous program,

A(~)

is read as 5.

In line

The following is

another example:
LISTNH
l~ DIM V(128)
15 INPUT "HOW MANY
2~ FOR 1=1 TO V(~)
25 INPUT V(I)
3~ NEXT I
35 CHANGE V TO A$
4~ PRINT A.$.: END
5~ END
READY

CHARACTERS";V(~)

RUNNH
HOW MANY CHARACTERS? 3
? 67
? 64
? 87
C@W
READY

Numbers which have no character equivalent in Table 5-2 do
not cause a character to be printed.
5.3

STRING INPUT
The READ, DATA, and INPUT statements can be used to input string

variables to a program.
l~
2~

For example:

READ A$, B, C, D
DATA 17, 14, 13.4, CAT

causes the following assignments to be made:
A$
B
C

the character string "17"

= 14

13,4
reading D as CAT causes an error message to be printed

Quotation marks are necessary around string items in DATA statements
only if the string contains a comma or if embedded blanks within the
string are significant.

Quotes (single or double) are always

acceptable around string items, even though not always necessary.
example, the items in line 40 in the following program are all
acceptable character strings and would be read

5-7

as printed.

For

LISTNH
l~ READ A$,B$,C$,D$,E$
2~ PRINT A$iB$iC$iD$iE$
3~ PRINT A$,B$,C$,D$,E$
4~ DATA "MR. JONES" ,MISS SMITH, "MRS. BROWN", "MISS",

"MR" I

READY
RUNNH
MR. JONESMISSSMITHMRS. BROWNMISS"MR"
MR. JONES
MISSSMITH
MRS. BROWN
n

MISS

"MR"

READY
A READ statement can appear anywhere in a multiple statement line,.
but a DATA statement must be the only statement on a line.

See also

the section on MAT READ which reads matrices (either numeric or
string) section 8.1.
The INPUT statement is used to input character strings exactly
as though accepting numeric values.

For example:

1.0 INPUT "YOUR NAME" iNS, "AGE" iA
is equivalent to
l~

PRINT "YOUR NAME" i
15 INPUT N$
2~ PRINT "YOUR AGE"i
25 INPUT A
Another feature of the INPUT statement when used with character
string input is the INPUT LINE statement of the form:
line number

INPUT LINE <string variable>

For example:
1}1 INPUT LINE A$
which causes the program to accept a line of input from the terminal
up to 72 characters long (the length of the terminal line) containing
embedded spaces, punctuation characters, or quotes.

Any characters

are acceptable in a line being input to the program in this manner.
The program can then treat the line as a whole or in smaller segments
as explained in section 5.5 which describes string functions.

5-8

When inputting or reading strings, leading blanks are ignored
unless enclosed in single or double quotes.
5.4

STRING OUTPUT
When character string constants are included in PRINT statements,

only those characters within quotes are printed.
trailing spaces are added.

No leading or

For example:

LISTNH
1.0 X=1 . .0:Y=2 . .01
2.0 PRINT "A = "; X "B
3.0 PRINT "DONE"
4.0 END

READY
RUNNH
A = 1
DONE

2 . .01

READY
Semicolons separating character string constants from other list items
are optional.

In line 10 above the variable Y is not separated from

the character string " B = "
Character string output can also contain the string functions
described in section 5.5.
5.5

STRING FUNCTIONS
Like the intrinsic mathematical functions found in BASIC,

BASIC-Plus contains various functions for use with character strings.
These functions allow the program to access part of a string, determine the length attribute of a string, generate a numeric string
or value given a numeric value or string, search for a substring
within a larger string, and other useful operations.

(These func-

tions are particularly useful when dealing with whole lines of
alphanumeric information input with an INPUT LINE statement.)

The

various functions are summarized in Table 5.3.
5.5.1

User Defined String Functions
Functions can be written (see section 3.7.3 and 9.1)

containing

string variables in the same way as they are created for numeric
variables.

The name of the function is indicated as being a string

function by the $ character after the function name.

5-9

TABLE 5.3
String Functions
Meaning

Function Code
LEFT (A$ ,N)

Indicates a substring of the string A$ from the
first character to the Nth character (the leftmost
N characters of the string A$) •

RIGHT (A$.,N)

Indicates a substring of the string A$ from the
Nth character to the last character in A$ (the
rightmost characters of the string A$ starting
with the Nth character).

MID (A$ ,Nl ,N2)

Indicates a substring of the string A$ starting
with character Nl and N2 characters long (the
characters between and including the Nl to Nl+N2-'
characters of the string A$) •

LEN (A$)

Indicates the number of characters in the string
A$ (including trailing blanks).

Indicates a concatenation operation. For example:
"ABC" + "DEF" is equivalent to "ABCDEF"
"12" + "34" + "56" is equivalent to "123456".

CHR$ (N)

Generates a character string having the ASCII
value of N (see Table 5.2).
For example: CHR$(40)
is equivalent to "(". Only one character can be
generated.

ASCII (A$)

Generates the ASCII value of the first character
in A$. For example, ASCII ("X") is equivalent to
88, the ASCII value of X.

DATE $ (~)

Indicates the current date in the form:
12-JUN-71
This quantity can be printed on output by simple
reference to the function.

INSTR(Nl,A$,B$)

Indicates a search for the substring B$ within
the string A$ beginning at character position Nl.
Returns a value of ~ if B$ is not in A$, and the
character position of B$ if B$ is found to be in
A$ (character position is measured from the
start of the string) ~

SPACE$ (N)

Indicates a string of N spaces.

NUM$ (N)

Indicates a string of numeric characters representing the value of N as it would be output by
a PRINT statement. For example: NUM$(l.~~~~) = 1.
etJ >. . . .'C.IUt 81- O/: . , .. . .
Computes the numeric value of the string of
numeric characters A$.
If A$ contains any character not acceptable as numeric input with the
INPUT statement, an error results. For example:
VAL ( "15" ) =15

~Q$. _

G&tS A LpO~4 i'a~
I~ -rwE slG'JI& (Jol ..
VAL (A$)

TIME $ (~)

,.". *' ......

Generates the time of day as a string of the
form:
12:59 AM
5-10

For example, the following multiple line function (see section
9.1) returns the string which comes first in alphabetical order:
l~ DEF FNF.$A$,B$)
FNF$=A$
IF A$>B$ THEN FNF$=B$
FNHND

2~
3~
4~

The following function combines two strings into one string:
l~

DEF FNC$(X$,Y$)=X$+Y$

Numbers cannot be used as arguments in a function where strings
are expected or vice versa.
8~

The following line is unacceptable.

LET Z=FNA$(4)

The following code is a string function which returns the leftmost 5 digits from the sum of 3 arguments:
75 DEF FNA$(X,Y,Z> = LEFT (NUM$ (X+Y+Z) ,5)
8~ PRINT FNA$(lE6,lE5,lE4)
The output of line 80 looks as follows:
lll~~

5-11

CHAPTER 6
INTEGER VARIABLES AND INTEGER ARITHMETIC

6.1

INTEGER VARIABLES
Normally, all numeric values (variables and constants) specified

in a BASIC program are stored internally as floating point numbers
(three words per value).

If operations to be performed deal with

integer numbers, significant economies in storage space can be
achieved by use of the integer data type (which uses only one word
per variable).

Integer variables (and constants) can assume values

in the range -32,768 to +32,767.
A constant, variable, or function can be specified as an integer
type by terminating its name with the % character.

6.2

100%

FNX%(Y)

-4%

Al%

FNL%(N%,L%)

For example:

INTEGER ARITHMETIC
Arithmetic performed with integer type variables is performed

modulo 2t15.

The number range -32,768 to +32,767 is treated as

continuous with the number after +32,767 equal to -32,768.

Thus,

32767 + 2 = -32767 and so on.
~nteger

division forces truncation of any remainder; for

example 5/7=0 and 199/100=1.

Operations can be performed in which

both integer and floating point data are freely mixed.

The result is

stored in the format indicated as the resulting variable, for
example:
25 LET X%

N% + FNA(R)*2

The result of the expression on the right is truncated to provide
an integer value for X%.
As another example, the statement below:
l~

PRINT 2/4, 2%/4, 2/4%, 2%/4%

6-1

when executed causes the following to be printed:

.5
6.3

INTEGER I/O
Input and output of integer type variables is performed in

exactly the same manner as operations on floating point variables.
(Remember that in cases where a floating point variable has an
integral value i t is automatically printed as an integer but is still
stored internally as a floating point number and hence takes more
storage space.)
l~
2~
3~

For example:

READ A, B%, C, D%, E
PRINT A, B%, C, D%, E
DATA 2,3,4.~,5.7,6.B

when executed prints:
2

6.4

6.B

USER DEFINED INTEGER FUNCTIONS
Functions can be written to handle integer variables as well as

floating point variables (see sections 3.7.3 and 9.1).

The function

is defined to be of integer type by following the function name with
the % character.
A function to return the remainder when one integer is divided by
another is shown below:
l~

DEF FNR%(I%,J%)

I%-J%

* (I%/J%)

and could be called later in a program as follows:
l~~

PRINT FNR% (A%, 11%)

Integer arguments can be used where floating point arguments
are expected and vice versa.

However, strings cannot be used where

numbers are required (or vice versa).
75 DEF FNA$(X%) = X%-l
B~ LET Z = FNA%(12.34)
is acceptable.

Z equals 11 after line BO has been executed.

6-2

6.5

USE OF INTEGERS AS LOGICAL VARIABLES
Integer variables can be used within IF statements in any place

that a relational expression can appear.

An integer value of ~,

corresponds to the logical value FALSE, and non-zero integers are
defined to be TRUE.

Any logical operators specified (AND, OR, NOT,

XOR, IMP, EQV) operate on logical data in a bitwise manner; thus the
integer -1%

(which is represented internally as sixteen binary ones)

is normally used when a TRUE value is required.
Logical values generated by BASIC always have the values -1% (TRUE)
and fl%

(FALSE).

The following Immediate Mode sequence illustrates the use of
integers in logical applications:
IF -1% THEN PRINT "TRUE" ELSE PRINT "FALSE"
TRUE
READY
IF -1% AND fl% THEN PRINT "TRUE" ELSE PRINT "FALSE"
FALSE
READY
IF 4% AND 2% THEN PRINT "TRUE" ELSE PRINT "FALSE"
FALSE
READY
IF -1% IMP -1% THEN PRINT "TRUE" ELSE PRINT "FALSE"
TRUE
READY
IF l<fl XOR -1% THEN PRINT "TRUE" ELSE PRINT "FALSE"
-PiIrl36E leU,:,'
READY

6-3

CHAPTER 7
DATA STORAGE CAPABILITIES

7.1

FILE STORAGE
Thus far, techniques have been presented for entering data into

a program as it is written (via READ and DATA statements) or when i t
is executed (via the INPUT statement).

Both of these techniques

pose operational problems when the amount of data a program reads
or writes is increased beyond a few items.

In order to alleviate

these problems, BASIC-Plus provides the user with a facility to
define Input/Output files.
A BASIC-Plus file consists of a sequence of data which is transmitted to (or from)

a BASIC program from (or to) an external Input/

Output device connected to RSTS-ll.

The external device can be the

user's terminal, some other terminal, the RSTS system disk, a line
printer, magnetic tape, or high-speed paper tape equipment.

Each

file has both an external name by which it is known within the system
and an internal file designator (a number used to refer to the file
within the program).

A special statement (OPEN, see section 7.4) is

used to associate an external name with an internal designator.
An external file name is completely specified with the following information:

device:fiZename.extension [proj,progJ
where the device can be one of the following:
~f:

-BS*-:

011/\'

D~A~

pa.:' ~
pp. ~:

DTA7.

L..r:~

c,/Z: ~
t1(2; ~
j(.&: .~
ICS.1! ~:

system disk
DECtape units 0 to 7
high-speed paper tape reader
high-speed paper tape punch
line printer
card reader
mark-sense card reader
user's terminal
terminal n in the system
system library

tM"';-~ I.,A.A:I- ""

7-1

The filename is a six character (maximum) alphanumeric name.

The

extension is a three character (maximum) alphanumeric file name
extension usually specifying the type of file. The extensions used
by the system are as follows (the user can create his own extensions) :
.BAS

BASIC source program, ASCII format

.BAC

Compiled BASIC program, binary format

.TMP

System scratch file for temporary use

A user can have up to 12 files open (with internal designators
1 through 12) for access at any given time.
a buffer within core storage.
indicated in Table 7-1.

Each open file consumes

The buffer sizes for various devices are

If a buffer cannot be created for a file, due

to a lack of storage space in core, then the file cannot be opened.
(The process of opening a file is described in section 7.2)

Table

7-1

DEVICE BUFFER SIZES
Device

Buffer Size

0; :

DSl'\;

256

words

G~.

B'fflfn.

words

P/2..:

PTt<:

256
64
64
64
64

Pt" .~
'- p ~ ~
/t::& ~

7.2

'f'f:t •

words
words
words
words

OPEN STATEMENT
The OPEN statement is used to associate a file on a bulk storage

device or an I/O device with an internal file designator.

This allows

the file to be readily referenced in INPUT, PRINT, and (in some cases)
DIM statemepts.
line number

The format of the OPEN statement is as follows:
'INPUT I ~
OPEN <string> ~OR LOUTPuis AS FILE<expression>

7-2

For example:

l~ OPEN "piR:" FOR INPUT AS FILE 1
2~

INPUT #1, A$

Line number 10 causes the paper tape reader to be opened as an input
source with the internal file designation 1.

Line number 20 causes

input to be accepted from file #1, and the input is associated with
the variable A$.
The formats for the INPUT and PRINT statements to be used with
the OPEN statement are as follows:

line number

INPUT

#<expression>~<list>

line number

#<expression>~<list>

where the expression is the same expression present in the OPEN
statement (the internal file designator) and the list is a list of
variable names (or constants as explained in the sections on the
PRINT and INPUT statements).

(The virtual matrix dimension statements

reference OPEN statements without the FOR INPUT or FOR OUTPUT
phrase, as explained later.)
The string portion of the OPEN statement can be specified as
a string constant (in quotes) or as a variable (with its value
deferred until program execution).

The string portion indicates the

device on which a file is to be opened.
RSTS-ll distinguishes between two kinds of devices:

those that

are directory-structured (disk and DEctape) and those which are not
(all others).

When indicating a file for either

input or output on

a directory structured device, it is necessary to specify both a
device name and a file name (and, optionally, an extension).

non-directory structured devices, the device name alone identifies
the file.

Thus:

of: ~:

is insufficient information to specify a file

OP.'-BSit": FRED

is sufficient to specify the file FRED on the disk

pp;~

uniquely specifies the high-speed punch

PP.~:FOO

specifies the high-speed punch, and FOO is ignored

File name syntax is such that the device name DSK: is not required

7-3

if a file name is specified.

Thus:

DSK:FOO
is equivalent to:
FOO
When a device is not specified, a file name alone always indicates
the disk as a default storage device.

However, to store a file on

DECtape, the device must be specifically indicated:
DTA4:FOO
The following sequence is useful and allows for easy change in
the device to be used before program execution begins:
1.0 LET I$ = "PTR:"
2.0 OPEN I$ FOR INPUT AS FILE 1
3.0 INPUT #1, A$
If a file being opened for input does not exist, an error
message is returned.

If a file being opened for output does not

exist, it is created.

If a file for output already exists and is not

write-protected, it is deleted and recreated.
If an assignable device is referenced in any OPEN statement and
that device is unavailable for assignment, an error message is printed.
File names used in an OPEN statement are composed of up to six
alphanumeric characters with an extension of up to three alphanumerics.

Thus, an output file could be created as follows:
1.0 OPEN "DSK:SCRTCH.TMP" FOR OUTPUT AS FILE Nl

Thereafter, reference can be made to file SCRTCH.TMP on device DSK:
as follows

(notice that the internal file designator is represented

as a variable, although its value must still be between 1 and 12):
1.0.0 PRINT #Nl, A$, B$
The internal file designator (following the # character in the

7-4

INPUT or PRINT statements) is always in the range 1 to 12.
#~

designator
File

is, by definition,

~lways~?p~~

File

as the user's terminal.

cannot be closed or opened as any other device or file.

Use of file
l~

is indicated below (no OPEN

INPUT

#~,

is necessary):

is equivalent to:
IJl INPUT A$
It is sometimes useful to be able to request keyboard input
without having the "?" prompting character printed first.

This can

be accomplished by opening the user's terminal ("TTY:") on some
internal file designator other than Jl, since the "?" is only generated
for input requests on file

#~,

as shown in the following example:

LISTNH
l~ OPEN "TTY:" AS FILE 1
15 PRINT "WITH USE OF INTERNAL FILE DESIGNATOR:"
2Jl PRINT "TYPE YOUR NAME ";
3Jl INPUT #1, A$
4Jl PRINT "FOR COMPARISON, WITHOUT FILE DESIGNATOR:"
4 5 INPUT "TYPE YOUR NAME "; A$
READY
RUNNH
WITH USE OF INTERNAL FILE DESIGNATOR:
TYPE YOUR NAME CHARLIE BROWN
FOR COMPARISON, WITHOUT FILE DESIGNATOR:
TYPE YOUR NAME ? CHARLIE BROWN
READY
If a file is being opened for both input and output or to be
referenced as virtual disk matrices (see section 7.5), the form:

line number
is used.

OPEN<string>AS FILE<expression>

If the file indicated by the name "string" is found, it

will be used and, if it is not found, it will be created.
When a program uses a statement such as:

5Jl OPEN "FOO" AS FILE 4

7-5

it can perform input and output to that file.

However, such a file

(FOO on the system disk) can only be referenced in a sequential
fashion.

If data is already in the file, it can be read via INPUT

statements similar to the manner in which a READ statement pulls
data from the DATA statement pool.

Any attempt to use a PRINT state-

ment with the file FOO will work only if there is nothing already in
that file.

If data already exists in the file FOO, a PRINT statement

will begin to write over any data beyond the point where the INPUT
stopped.

This is not a recommended technique since the entire file

will be garbled and useless.
7.3

OUTPUT TO VARIOUS DEVICES
In order to direct output to a device other than the user terminal,

the PRINT command is formatted as follows:

Zine number

PRINT #<expression>,<Zist>

where the expression is the internal file designator of a previously
opened output file (see section 7.2).

The list of information to be

output can include any of the output information described as
applicable to the PRINT statement.
l~
2~

For example:

OPEN "DATAl" FOR OUTPUT AS FILE 1
PRINT #1, "START OF DATA FILE"

The above lines open a file called DATAl on the disk with internal
file designator #1 (of 12 possible open files available in the system).
The first line in that file reads:

START OF DATA FILE •

To output a table of square roots on the line printer, the following program could be used:
LISTNH
l~ LET I$ = "LPT:"
2~ OPEN I$ FOR OUTPUT AS FILE 1
3~ PRINT #1, I,SQR(I) FOR I= 1 TO 5
4~ END
READY
RUNNH
The results would appear on the line printer as follows:

7-6

1
2
3

7.4

1.4142136
1. 732{J5fJ8

2.236.068

INPUT FROM VARIOUS DEVICES
Like the PRINT statement, the INPUT statement can operate upon

devices other than the user terminal.

Zine number

The form:

INPUT #<expression>,<Zist>

causes input to be accepted from the previously opened file or
device indicated in the expression (see section 7.1).

As long as

the value of the expression is non-zero, the specified file is read
through one of the 12 available user I/O buffers (internal file
designators).

If the expression is zero, or missing completely,

input is from the user terminal.

No? character is printed on the

terminal paper when input is requested from a device other than the
terminal, opened on file #{J.

For example:

lfJ OPEN IIpTR: II FOR INPUT AS FILE 3
2fJ INPUT #3, A$, B$
causes the strings A$ and B$ to be read from the high-speed paper
tape reader.
Note that spaces are ignored in input data.

If the user wants

to read numeric data from a file previously created (on disk or
DECtape, for example) he should insert commas in the data when he
prints the data in the file.

For example:

lfJfJ OPEN "DTA4 :LEN" AS FILE 1
llfJ PRINT #1, A " , " B " , " C
2fJfJ OPEN IIDTA4:LEN" AS FILE 1
21.0 INPUT #1, A,B,C
22.0 PRINT A,B,C
is an acceptable sequence to print three values onto a DECtape file,
read them from that DECtape file, and print the three values on the
user terminal.

As in the example above, once a file is opened i t

can be closed and reopened through the use of a second OPEN statement.

Reopening the file moves the positioned pointer within the

file back to the beginning of the file, so that the entire file

7-7

becomes available again for sequential referencing.

This serves

much the same function as a RESTORE statement would to the pool of
DATA statements.
7.S

VIRTUAL DATA STORAGE
Many applications require a capability to individually address

and update records on a disk file in a random (non-sequential)
manner.

AJ...'-'_V'"

_""""_,

VUlt;:.L

ClJ::-'J::-'..L...L.\...Cl~..L.Ull;::)

_ _ ..... ~ _ _ _

'n'\_ ..... ___ ".. . : __ 'I""r'\"""'__

____

lLLClY

\...U.L t::

.Lt::'-fI.1..L..Lt::

storage than is economically feasible.

lLLU.L t::

Y'Y"I_"""" __ "'"

"Lt::ULU.L Y

BASIC-Plus fills both these

requirements with its easy-to-use random access file system, called
virtual core.
Essentially the BASIC-Plus virtual core system provides a mechanism for the programmer to specify that a particular data matrix
is not to be stored in the computer's core memory, but within the
RSTS-ll file system, instead.

Data stored in files external to the

user program will survive, even after the user leaves his terminal,
and can be retrieved by name at a later RSTS-ll session.

Items

within the file are individually addressable, as are items within
core matrices.

In fact, it is the similar way in which data are

treated in both core and random-access files which leads to the name
virtual core.
The matrix format is used to store data because in a normal data
file, described earlier, the PRINT and INPUT statements deal only
with the next sequential data element.

A normal data file, then, is

much more limited in its applications and depends upon a strictly
sequential treatment of I/O.

With virtual data storage, the user

can reference any element of the file, no matter where in the file it
resides.

This random access of data allows the user program to

perform non-sequential referencing of the data for use in any BASIC
statement (which is to say that the virtual core matrices need not
be read into core to be available to the program for use).
In order for a matrix of data to exist in virtual core, it must
be declared in a special form of the DIM statement (placed in
program sequence somewhere after the corresponding OPEN statement) •
This special statement is as follows:

.tez:: ,..t

line number DIM #<0

(."t.,., ...1.)

p~r'QN>,<list>

where the &• • • • e' • is an integer constant between 1 and 12 and
7-8

corresponds to the internal file designator on which the program has
opened an internal file (see below and also section 7.2).

The variable

list appears as it would for a normal core resident matrix DIM statement.

Thus, a 100
l~

by 100
A(l~~

DIM #12,

matrix could be defined as:
,l~~

Floating point numbers, integers, and strings can all reside in
virtual core matrices.
virtual core file.

More than one matrix can be specified in one

For example:

25 DIM #1,

A(l~~~),

B%(2~~~),

C$(25~~)

which allocates space for 1000 floating point numbers, 2000 integer
numbers, and 2500 character strings (16 characters long each) .
One of the few differences in data handling between core and
disk matrices occurs in the storage of strings within string matrices
in virtual core.

Strings in the computer core memory are of variable

length from ~ to any arbitrary length.

Strings in virtual core are

of fixed length (all elements having a particular name are of the same
length).

This length can be defined by the programmer and varies from

1 character to 512 characters.

The system forces lengths to be a

power of 2:
1, 2, 4, 8, 16, 32, 64, 128, 256, 512
If the user indicates other than one of these values, he will receive
the next higher size.
l~

DIM #1,

Thus:

X$(l~)=

128

is the same as:
l~

DIM #1,

If no length is specified, a default length of 16 characters is
assumed.

The length attribute of virtual core strings is specified

in the DIM statement, uSing the notation:
15 DIM #1,

A$(l~~)

32,

B$(1~~)=4,

7-9

C$(l~~)

A$ consists of 101 strings of 32 characters each;

where

B$ consists of 101 strings of 4 characters each;
C$ consists of 101 strings of 16 characters each.
If a length attribute is given in a DIM statement for an in-core
string matrix, it is ignored, since core storage can be allocated
dynamically to hold a string of any length.
In order for the user to reference his virtual core file, he must
first associate one of his files

(known by name) with an internal file

designator from 1 to 12 (which is then used in the virtual DIM
declaration).

This is normally done with the following OPEN statement:

line number OPEN<string>AS

FILE<expression>

where the string is the name of a disk file and the expression
specifies an internal file designator; thus:
35 OPEN "FOO" AS FILE 1
associates the file named "FOO" with internal file 1.

If "FOO"

already exists, then the existing file is used; if there is no file
named "FOO" one would be created.

If the user wishes to destroy any

old "FOO" file, he can write:
35 OPEN "FOO" FOR OUTPUT AS FILE 1
which causes the file to be deleted if it already exists and recreated.
If the user wanted to be alerted that the file "FOO" is not present,
he could write:
35 OPEN "FOO" FOR INPUT AS FILE 1
which would cause an error message to be printed if "FOO" is not
found.
Recoverable errors will occur when using virtual core if the
user program does any of the following:
1.

Reference a virtual matrix without first opening the file.

Reference a non-disk file (for example, DECtape or the
line printer) as a virtual matrix.

"\Ava\ 'W~ li\d Moist b& <Soul 7-10"'~ C:"\i';"'1 J rI- tl.. f.le il ....b.
\1(.,1

Ccftecil1 w~

.... _.,. ..tJ.

Exceed virtual core, that is, define a matrix which is
bigger than the amount of available disk storage on the
system or the amount which the user is allowed to own.

Sophisticated users are urged to read Appendix E which describes the
system implementation of the virtual core processor.

A mastering of

this information will produce programs which utilize the system
resources in a highly efficient manner.
As an example of virtual core usage, consider the problems of
implementing an information retrieval system for a small organization.
There might be 1000 employees, each needing a 256-character record
containing the name, horne address, phone, work station, and phone
extension of the employee.

Rather than order the records in the file,

it is decided to maintain a separate index file containing only badge
numbers.

The order of employee records in the master file is the

same as the badge number sequence in the index file.

Thus, to extract

information on an employee with badge n, we find his badge number in
the index file and use the index found to retrieve his data from the
master file.

Since the number of employees is small, integer data can

be used in the badge file; only alphanumeric data is stored in the
master file.
A program to print an employee's name, given his badge number,
might appear as follows:
l~
2~
3~

!PROGRAM TO LOOK UP NAMES IN MASTER FILE
!BADGE FILE
OPEN "BADGE" AS FILE 1
!MASTER FILE
OPEN "MASTER" AS FILE 2
4~
DIM #1, B%(l~~~)
!l~~~ BADGE NUMBERS
!l~~~ RECORDS, EACH 256
5~
DIM #2, A$(1~~~)=256
!CHARACTERS LONG
INPUT "BADGE NUMBER" ;E%
!GET EMPLOYEE NUMBER FROM TTY
6~
GOTO l~~ IF B%(I)=E% FOR 1=1 TO l~~~
!IS BADGE # IN FILE?
7~
PRINT "NO SUCH EMPLOYEE": GOTO 6~
!NO
8~
!YES
100 !WE NOW HAVE INDEX INTO FILE,I
R$ = A$ (I)
! BRING RECORD INTO CORE
ll~
!NAME IS FROM COLUMN 1.0 TO 25
12.0 PRINT "NAME ISII; MID(R$,l~,l5)
!NEXT ...
13.0 GOTO 6~
7.6

CLOSE STATEMENT
The CLOSE statement is used to terminate I/O to or from a device.

Once a file has been closed, it can be reopened for reading or writing
on any internal file designator.

All files are automatically closed

at the end of program execution.

The format of the CLOSE statement is

as follows:
line number

<expression>
7-11

Li-cs(f
RLiJ

do:u

iA.c"Y

wi· t. t.i 1(. ~.b.r. Io,.,,~ d,k /'1<-. Jo it~f
I'
'Z C (cH,zi (l,b'iJ) ~#.,- f~3r HLGid..

wy;te

0;,

.. a

-Gf· ftfe. ~ <aw c~ ~

Any number of files can be closed with a single CLOSE statement; if
more than one, they are separated by commas.

The expressioQ indicated

is the same expression used in the OPEN statement and indicates the
internal file designator.

By clfosing a file with the CLOSE state-

ment, the user frees more core storage space to open other files
maximum of 12 depending upon the space available).
255 CLOSE
345 CLOSE

For example:

2, 4
L~

Line 255 above closes the files opened on internal device designators
2 and

Line 345 closes the file open on internal device designator

l~.

7.7

NAME-AS STATEMENT, FILE PROTECTION AND RENAMING
The NAME-AS statement is used to assign protection codes to a

file

(and to rename an existing file).

The format of the command is

as follows:

line number NAME<string>As<string>[<protection>J
The specified file

(the first string indicated) is renamed (as the

second string indicated).

A file protection code can be specified

within typed angle brackets, although it is not required.

If a new

file protection is specified, it is reflected in the protection
assigned to the renamed file.
Each user in the system is given a unique project-programmer
number which identifies him to the system.
of the form

[1~,2~J

This is a two-part number

where "10" is the user's project or group number

and "20" is his individual programmer number.

Files are protected

from various user classes determined by the project-programmer number.
Specifically, files can be protected against:
the owner (creator)
other programmers in the owner's group
all others

The protection is part of the second string and is itself a string.

7-12

The following table contains the codes used to determine file
protection.
Protection
Against

Code

Meaning

owner

read protect

owner

write protect

group

read protect

group

write protect

others

read protect

others

write protect

The file protection can be specified as the sum of any combination of
these values; for example:
l~~

NAME "FOO" AS "FOO<48>"

would deny access to the fileFOO to anyone not in the owner's group
( 32 plus 16).
275

NAME "DTA2: MATRIX" AS "MAT2"

renames the file MATRIX on DECtape 2 as MAT2 (in this case on DECtape
2; the device specification need not be repeated).

7.8

KILL STATEMENT
The KILL statement is of the form:

line number

KILL<string>

and

causes the file named string to be deleted from the user's file

area.

For example, when the user has completed all work with the

file XYZ.TMP on the system disk, he could remove the file from
storage by executing the following statement:
455 KILL "XYZ.TMP"
A

user is not allowed to KILL a file that is write-protected

against him.

(He must use the NAME-AS statement to change its protec-

tion first.)

7-13

CHAPTER 8
MATRIX MANIPULATION

The following chapter deals with intrinsic functions to handle
matrices.

Matrices can be composed of variables of any type.

single matrix, however, is composed of a single type of data:
ing point, integer, or character string.

A
float-

All MAT operations ignore

the zero element of each matrix (A(9), B(9,9».
8.1

MAT READ STATEMENT
The MAT READ statement is used to read the value of each element

of a matrix from DATA statements.

The format of the statement is as

follows:

line number

MAT READ<list of matrices>

Each element in the list of matrices indicates the maximum amount of
the matrix to be read (which cannot be greater than the dimensioned
size of the matrix).
commas.

The individual elements are separated by

If the matrix name is used without a subscript, the entire

matrix is read.
l~
2~

For example:

DIM A (29,29)
MAT READ A

The above lines read a twenty by twenty matrix of floating point
data.

Data is read in row by row; that is, the second subscript

varies most rapidly.
29

If line 30 had read:

MAT READ A(5,15)

a 5 by 15 matrix would be read (the remaining elements of A are zero).
8.2

MAT PRINT STATEMENT
The MAT PRINT statement prints each element of a one or two

dimensioned matrix.

The statement is of the following form:

line number

MAT PRINT #<expression>, <matrix name>

If the matrix name consists of an unsubscripted matrix name, the
entire matrix is printed.

If the matrix name is subscripted, then

the subscript indicates the maximum size of the matrix to be printed.

" ..~,...U.... -~1 1M. -ic! '" s"..8-1
~~ M tl...

<..a.t,.~ "... ,.~~ ::> .

Where the expression is not included, output is to the user terminal.

If the matrix name is followed by a semicolon (;), the values
are printed in a packed fashion; otherwise, each element is printed
in its own zone.
DIM A(l~,l~), B(2~,2f,J)
MAT PRINT Ai
MAT PRINT B(1~,5)

If,J
l2f,J
l3f,J

!PRINT
!PRINT
!LINE

l~*l~ MATRIX, PACKED FORMAT
1~*5 MATRIX, 5 ELEMENTS PER

In order to direct the output of the MAT PRINT statement to a
device other than the user terminal, an internal file designator is
used following the opening of such a file.

For example:

DIM A(2~,5) ,B(1~,2~)
OPEN "LPT:" AS FILE 2
MAT PRINT #2, A
MAT PRINT #2, B;

If,J
ll~
l2~
l3~

The above lines cause the matrices A and B to be output to the
line printer.

Remember only one matrix can be output by one MAT

PRINT statement.

In order to perform a jump to the top of the next

line printer page, send a CTRL/L as part of a PRINTER statement to
the line printer, or type CHR$(12) at the end of a PRINT statement.
It is also possible to obtain printing of both row and column
matrices.

For example:
l~
2~
3~
4~

DIM A(7), X(5)
MAT READ A, X
MAT PRINT Ai:PRINT: MAT PRINT X
DATA 21,22,23,34,35,36,37,51,52,53,54,55
5~ END

RUNNH
21

51
52
53
54
55

8-2

The format:
MAT PRINT V
prints the matrix V as a column matrix.
MAT PRINT V,
prints the matrix V as a row matrix, five values per line, while
MAT PRINT Vi
prints the matrix V as a row matrix, closely packed.
8.3

MAT INPUT STATEMENT
The MAT INPUT statement is used to input the value of each

element of a matrix from a specified input device.

Where no particu-

lar device is specified, the input is accepted from the user terminal.
For example:
2~~

MAT INPUT A(2~)

will cause BASIC to accept 20 floating point values as elements of the
matrix A from the user terminal.
A statement of the format:

line number

MAT

INPUT~<expreSSion>J <variable list>

causes the input to be read from a file or device, indicated by the
expression, which has been previously opened.

(For details, see the

sections on the OPEN and INPUT statements, sections 7.1 and 7.4)
If the input is to be from the user terminal, a ? character is
printed to indicate that the program is ready to accept input.

input is from another specified device or file, no ? character is
printed.
Depending upon the variable names, the MAT INPUT statement can
allow the input of integer, floating point, or character string

8-3

values.

For example:
2fJfJ OPENIDTAl:MATN" FOR INPUT AS FILE 4
DIM #4, N$(~9)
21fJ MAT INPUT #4, N$

2~S

reads 30 elements of the file MATN on DECtape unit 1 and equates
them with the elements of the character string matrix N.

8.4

MATRIX INITIALIZATION STATEMENT
A matrix initialization statement allows the user to create

initial values for the elements of a matrix.

The statement is of

the form:
line number

MAT<name>=<va lue> [<DIMl,DIM2)]

The name element is the name of a particular matrix, and the optional
DIMI and DIM2 specifications indicate the maximum size of the matrix
elements which are to be initialized to the value specified.

The

value can be one of the following:
Value

Meaning

ZER

Sets all elements of the matrix to fJ (this
is true of all matrices when they are first
created)

CON

Sets all elements of the matrix to 1

IDN

Sets up an identity matrix

All matrices used in a matrix initialization statement must be
previously declared in a DIM statement.

If no dimensions are in-

dicated (DIMI and DIM2 are not specified), then the maximum dimensions of the matrix are assumed.
l~
IfJ~
l~l
1~2

For example:

DIM A(lfJ,lfJ}, B(IS}, C(2fJ,2fJ}
MAT A
ZER
!SETS ALL ELEMENTS OF A=~
MAT B = CON (l~)
!SETS FIRST IfJ ELEMENTS OF B=l
MAT C
IDN (l~ , 1.0)
! C MUST BE SQUARE

It should be noted, however, that these instructions have no
effect on row and column zero.

Thus, the following instructions:

8-4

l~ DIM M{2~,7)
2~ ~T READ M(7,3)

l~~

ll~ ~T

M=CON
M=ZER{15,7)

2~~

M=ZER(16,1~)

first read in a 7 by 3 matrix for M.

Then they set up a 7 by 3
matrix of alII's for M (the actual dimension having been set up as
7 by 3 in line 20). Next they set up M as a 15 by 7 all-zero matrix.
{Note that although this is larger than the previous M, it is within
the limits set in 10.}

An error message results because of line 200.

The limit set in line 10 is {20+l} x {7+l} = 168 components, and in
line 200 the program calls for (16+l) x (10+1) = 187 components.
Thus, although the zero rows and columns are ignored in ~T instructions, they playa role in determining dimension limits.
2~~ ~T

For example:

M=ZER(25,5}

would not yield an error message.
Perhaps it should be noted that an instruction such as
MAT READ M(2,2} which sets up a matrix and which, as previously mentioned, ignores the zero row and column does, however, affect the zero
row and column.

The redimensioning which may be implicit in an in-

struction causes the relocation of some numbers; therefore, they may
not appear subsequently in the same place.

Thus, even if we have

first LET M(l,O) , M(2,O) = 1, and then ~T READ M(2,2), the values
of M{l,O} and M(2,0} now are 0.

Thus, when using MAT instructions,

it is best not to use row and column zero.
8.5

MATRIX CALCULATIONS
Mathematical operators and two intrinsic functions are available

for use with matrices.
8.5.1

Matrix Operations
The operations of addition, subtraction, and multiplication can

be performed on matrices using the cornmon BASIC mathematical symbols.
Eac~

of the matrix operation statement is begun with the word

MAT and followed by the expression to be evaluated.

Each of the

matrices involved must be predefined in a DIM statement.

The sub-

scripts of the matrices need not be indicated in the statement,
although if two matrices are not conformable to an operation, a subset of one matrix can be indicated as part of the operation.

8-5

The following operation is acceptable:
1.04 DIM A(5.0) , B(25), C(25)
1.05 MAT C = A + B
Multiplication of conformable matrices is indicated as follows:
11.0 MAT C = A*B
By conformable matrices is meant that the number of columns in matrix
A is equal to the number of rows in matrix B.

The operation A =A*B is

illegal.
Scalar multiplication of a matrix is performed as follows:
115 MAT C = (K)*A
Each element of matrix A is multiplied by the scalar value (constant,
variable, or formula) K, indicated in parentheses.

If K is not speci-

fied, matrix A is copied into matrix C (providing sufficient space is
available for matrix C) as shown below:
12.0 MAT C = A
The form A=(K)*A is legal.
8.5.2

Matrix Functions
Functions exist for the performance of transpoSition and inver-

sion of matrices.
15.0 MAT C = TRN(A)
causes matrix C to be set equal to the transpose of matrix A.
C(I,J)

A(J,I) for all I,J.
151 MAT C = INV(A)

causes C to be computed as the inverse of matrix A (A must be a square
matrix).

After the inversion is complete, the function DET is set to

the determinant of matrix A and can be tested to decide whether a
singularity was found.
variable in any formula.

The value of DET, then, can be used as a
For example:

2.0.0 MAT A = INV(X) : Dl=DET
21.0 MAT B = INV(Y) :D2=DET
22.0 IF Dl<>(-D2) GOTO 34.0 ELSE PRINT "RELATIONSHIP TRUE"

8-6

~l MAT C

INV(A)

~'"

causes C to be

square matrix).

com~ed

as the inverse of matrix A (A must be a

"""'-

After"'t.l:!.~

inversion is complete, the function DET

is set to the determinant -'cf-.matrix A and can be tested to decide
whether a singulari ty was

fou~"d':''--''The value of DET, then, can be

used as a variable in any formula.

FCl$, __ ~xample:

2fJj.,cMAT A = INV (X) : DI=DET

.,./21fJ MAT B = INV (Y) : D2=DET
/ 22fJ IF DI<>(-D2) GOTO 34fJ ELSE PRINT "RELATIONSHIP
TRUE"
.....
Matrix inversion, like the other BASIC Plus matrix operations,
does not operate on the elements of the row fJ and column fJ of the
matrix; unlike the other operations, inversion destroys the previous
content of these elements.

8-7

CHAPTER 9
ADVANCED STATEMENT FEATURES

9.1

DEF STATEMENT, MULTIPLE LINE FUNCTION DEFINITIONS
In Chapter 3

the DEF statement is described as having the

ability to create a one-line function which the user can call as an
element in a BASIC statement.

The user has, by now, probably felt the

need for a user-defined function which can extend onto more than one
line; such a facility is available.

The format for a multiple line

definition is as follows:

line number
line number
line number

FN<identifier>«dummy arguments»
<body of definition>
FN<identifier>= <expression>
FNEND
DEF

The multiple line DEF function is distinguished from the one line use
functions by the absence of an equa.l . sign following the function name
on the first line.

.}.'V~~

(From zero to Q~~~~ arguments of any type or

mixture of types can be used.)

The value returned by the function is

the value of FN<identifier> at the time the FNEND statement is
encountered.

Somewhere within the multiple line definition there

must be a statement of the form:

line number [LET} FN<identifier> = <expression>
It is the value of this expression which is returned as the value of
the function.
The example function below determines the larger of two numbers
and returns that number.

The use of the IF-THEN statement is

frequently found in multiple line functions as follows:
l~
2~
3~
4~
5~

DEF FNM(X,Y)
LET FNM = X
IF Y<=X THEN
LET FNM = Y
FNEND

9-1

As another example, the following function computes N-factorial:
LISTNH
l~ DEF FNF (M)
2~ IF M=l THEN FNF=l ELSE FNF=M*FNF(M-l)
3~ FNEND
35 INPUT "VALUE FOR FACTORIAL";M
4~ PRINT M" FACTORIAL EQUALS "FNF(M)
READY
RUNNH
VALUE FOR FACTORIAL? 4
4 FACTORIAL EQUALS 24
READY
Any variable which is not an argument in a multiple line DEF function
has its current value in the user program.

Multiple line DEF functions

can be nested (one multiple line definition can reference another
multiple line definition or itself).

There must not be a transfer

from within the definition to outside its boundaries or from outside
the definition into it.

The line numbers used by the definition must

not be referenced elsewhere in the program.
The parameters with which a user defined function is called are
strictly formal; any attempt by the program to modify them will be
cancelled when the function exits to its calling program:
l~ DEF
2~ X=~

FNB (X)
:FNB=l.0
3~ FNEND
4~ A=l
5~ B=FNA(A)
6~ PRINT A, B
RUNNH
1
1.0
READY

Functions can be written in any type and can contain any variety
of argument types.

For example:

LISTNH
1.0 DEF FNA$(A,B,C)
2~ IF A>B GOTO 4~
3~ FNA$=CHR$(A+l) :GOTO 5~
4.0 FNA$=CHR$(A+C)
5f1 FNEND
6~ INPUT "VALUES FOR A,B,C";A,B,C
7~ PRINT "FNA$(A,B,C) = "FNA$(A,B,C)
(Cont.d next page)

READY

9-2

k)o\" IL- dU"ci;~;.,.., .~-t.......-t ~II k cnl~1rJ l..M ,,~
,JJ.t., J- tt.. 1M-J·,M "'"~ il ~,utIJ. Be.. (~t,I- .;" k *LIft1
~..

...

....

s.J.lJlllt,t' ",.• ., !

RUNNH
VALUES FOR A,B,C? 36,2,31
FNA$(A,B,C) = C
READY
9.2

ON-GOTO STATEMENT
The simple GOTO statement allows the user to unconditionally

transfer control of the program to another line number.

The ON-GOTO

statement allows control to be transferred to one of several lines
depending on the value of an expression at the time the statement is
executed.

The statement is of the form:

line number

ON <expression>

GOTO

4ist of line numbers>

The expression is evaluated and the integer part of the expression is
used as an index to one of the line numbers in the list.
5~

ON X GOTO

l~~,

2~~,

transfers control to line number
number

2~~

if X is 2, and to

3~~

For example:

3~~
l~~

if the value of X is 1, to line

if X is 3.

Any other values of X

(other than 1, 2, or 3 in this example) cause a program error which
will terminate execution or cause the error subroutine specified via
the ON ERROR GOTO statement to be entered (see section 9.4 for details).
9.3

ON-GOSUB STATEMENT
The GOSUB and RETURN statements are used to allow the user to

transfer control of his program to a subroutine and return from that
subroutine to the normal course of program execution (see section 3.8
for details).

The ON-GOSUB statement is used in the same manner as

the ON-GOTO statement described in the previous section.

The state-

ment is of the form:

line number

ON <expression> GOSUB <list of line numbers>

Depending on the integer value of the expression, control is transferred to the subroutine which begins at one of the line numbers
listed.

Encountering the RETURN statement after control is transferred

in this way allows the program to resume execution at the line following the ON-GOSUB line.
Since it is possible to transfer into a subroutine at different

9-3

points, the ON-GOSUB statement could be used to determine which
portion of the subroutine should be executed.
An example of the statement follows:
8~

ON X GOSUB

9~~,933,1~14

When line 80 is executed, the value of X being either 1, 2, or 3 will
cause control to transfer to line 900, 933, or

1~14

respectively.

If X is not equal to 1, 2, or 3, the error message.
ON STATEMENT OUT OF RANGE AT LINE

is printed.
9.4

ON ERROR GOTO STATEMENT
Certain errors can be detected by BASIC while executing a user

program.
errors

These errors fall into two broad areas:

(such as division by

computational

and Input/Output errors (reading an

end-of-file code as input to an INPUT statement).

Normally the

occurrence of any of these errors causes termination of the user
program execution and the printing of a diagnostic message.
Some simple mathematical errors are corrected (or compensated
for)

automatically by BASIC.

Some applications, however, may require

the continued execution of a user program after an Input/Output
error occurs.

In these situations, the user can execute an ON ERROR

GOTO statement within his program.

This statement tells BASIC that

a user subroutine exists, beginning at the specified line number,
which will analyze any I/O (or computational) error encountered in
the program and possibly attempt to recover from that error.
The format of the ON ERROR GOTO statement is as follows:

line number

ON ERROR GOTO <line number>

If an error does occur, the user program execution is interrupted and
the error subroutine is started at the line number indicated.
variable ERR in the program assumes one of the values listed in
Table 9.1.

9-4

The

Table 9.1
USER RECOVERABLE ERRORS
(F)

= Execution terminated if no ON ERROR GOTO statement is present
in the program.

ERR

4~
~4

Message Printed

Meaning

BAD DIRECTORY FOR DEVICE

File lookup is impossible.

ILLEGAL FILE NAME

Name contains embedded blanks or
non-acceptable characters.
(F)

FILE IS CURRENTLY OPEN

User cannot write in a file while
other users are reading it.
(F)

NO ROOM ON DEVICE

No storage space to store more
data.
(F)

CAN'T FIND FILE

The file to be opened for input is
not present on the specified
device.
(F)

NOT A VALID DEVICE

The specified device is not
present in the system.
(F)

I/O CHANNEL ALREADY OPEN

The channel must be closed before
another OPEN can occur on that
channel.
(F)

DEVICE NOT AVAILABLE

Another job is using the
specified device.
(F)

I/O CHANNEL NOT OPEN

The user tried to read or write on
an unopened channel!
(F)

PROTECTION VIOLATION

The user tried to read or write a
file protected against him or open
another user's file that was both
read and write protected against
him.
(F)

END OF FILE ON DEVICE

User has tried to read beyond the
end of his data.
(F)

OPERATION ABORTED

Serious I/O failure.

DATA ERROR ON DEVICE

parity error detected on operation.

DEVICE OK?

Device seems to be off-line or in
need of service.
(F)

TELETYPE WAIT EXHAUSTED

User did not -respond on Teletype
within allotted time.
(F)

FILE OF SAME NAME EXISTS

User is renaming a file with a
name already in use.
(F)

-i"'I VIRTUAL CORE NOT ON DISK
~

ry-cfR~gA::b

~9RE

(,,.''2£ A '-;' '1';-0

E*SSI3Bf3B
BI6

4~ ~

VIRTUAL ARRAY NOT OPENED

)7
\6

TOo MAIJ'1' 01 cvfPv-:' useaS
i L-Lf~<;A'-

vuo

u SelZ-

(F)

User has tried to use a non disk
device for a virtual core matrix.
There is not enough disk available
to store an entire virtual core
matrix.
(F)
Referenced virtual core matrix
without opening file first.
(F)

9-5

(F)

Table 9.1 (Cont.)
ERR

4b :M'

...J-r

4 B .,2'£

Message Printed

Meaning

ILLEGAL I/O CHANNEL

User has tried to open a channel
greater than 12.
(F)

LINE TOO LONG
FLOATING POINT ERROR

A record longer than 256 bytes was
read from an I/O device.
(F)
Underflow or overflow has occurred.

4' pr-

ARGUMENT TOO LARGE IN EXP

Inaccurate results will follow.

Sl>

ARGUMENT TOO LARGE IN SIN

Inaccurate results will follow.

5'1 ,2:f!)

INTEGER ERROR

Overflow has occurred.

'"v~

ILLEGAL NUMBER

A non-numeric character was
encountered in a number.

$"} .2:1"

TRANSCENDENTAL ERROR

Attempt to take log of
negative number.

IMAGINARY SQUARE ROOT

User requested square root of
negative number.
SQR(ABS(X))
returned.

SUBSCRIPT OUT OF RANGE

Undefined matrix element
referenced.
(F)

)Z"

5'4

5(.1/5"
Sb
S1 ~

C,w'J

OUT OF DATA

User has exhausted DATA list.

S8 ~

ON-STATEMENT OUT OF RANGE

The expression in an ON-statement
was less than 1 or greater than
the number of line numbers
specified.

59;C

NOT ENOUGH DATA IN RECORD

User tried to input more data then
existed in the next logical record
of file.

ILLEGAL UUO FOR USER

Invalid use of system function.

'%'

I';~

11AT121){

11J71!6erl. olll!/ZR.lJW

O/lJ;5.IOJ,)~"

(F)

~ I..tJtJ-r

When an error is encountered in a user program, BASIC checks to
see if the program has executed the ON ERROR-GOTO statement.

If this

is not the case, then a message is printed at the user's terminal and
the program proceeds (if the error does not cause execution to
terminate).

If the ON ERROR-GOTO statement was executed previously,

then execution continues at the specified line number where the
program can interrogate the variable ERR to discover precisely what
problem occurred and decide what action is to be taken.
After the problem is corrected (if this is both possible and
desired by the program), execution of the user program can be resumed
through use of the RESUME statement.

9-6

The RESUME statement causes the

program statement that originally caused the error to be reexecuted.
If execution is to be restarted at some other point within the
program (as might be the case for a non-correctable problem), the new
line number can be specified in the RESUME statement:
l~~~
l~~l

RESUME
RESUME

l~~

The first statement restarts the user program at the line in which the
error was detected, and is equivalent to the following statement:
l~~~

RESUME

Line 1001 above will restart the user program at line 100 (which can
be used to print some terminal message for that particular operation.
If there are portions of the user program in which any errors
detected are to be processed by the system and not by the user program,
the error subroutine can be disabled by executing the following
statement:

line number

ON ERROR GOTO

which allows the system to handle errors or, equivalently:

Zine number
in which case line

is assumed.

ON ERROR GOTO
Executing this statement causes the

system to treat errors as it would if no ON ERROR GOTO had ever been
executed.

(Anything other than a line number following the GOTO is

equivalent to ON ERROR GOTO

~.)

It is sometimes inconvenient to be continually turning the error
subroutine facility on and off.

For this reason, BASIC-Plus allows

the statement
ON ERROR GOTO

to be executed within the error subroutine itself.

Special treatment

is accorded this case, in that the disabling occurs retroactively; the
error which caused entry to the error subroutine is then reported
through the normal system error reporting facilities.

9-7

As an example of the usage of this feature, consider an application in which inexperienced students interact with a BASIC program.
These users may not know what to type at the terminal, and the program
may want to prompt them.

The program tells the system to allow up to

60 seconds for the user to respond (via the WAIT function, described
in section 9.10) and then to alert it that the user has not replied.
The program then prints additional information for the user.
l~
2~
3~

l~~~

1.0.01
1.01.0
1~2.0
1~3.0

1.04.0
9.5

ON ERROR GOTO l~~~
WAIT (6~)
INPUT "YOUR NAME" iN$

!SET UP ERROR ROUTINE
!6~ SECONDS TO RESPOND
!GET STUDENT NAME

!THIS IS THE ERROR HANDLING ROUTINE
IF ERR < > 15 THEN ON ERROR GOTO fiJ
: TIME ERROR HANDLER ONLY
PRINT
!SKIP TO NEW LINE
PRINT "PLEASE TYPE YOUR NAME"
PRINT "AND THEN HIT THE 'RETURN' KEY"
RESUME
!TRY AGAIN

IF-THEN-ELSE STATEMENT
The IF-THEN statement allows the program to transfer control to

another line or execute a specified statement depending upon a
specified condition.
The IF-THEN-ELSE statement is exactly the same as the IF-THEN
statement, except that rather than falling through to execute the line
following the IF statement, another line number or statement can be
specified for execution where the condition is not met.

The statement

is of the form:
!THEN< line number;: r
J
line number IF<condition> ; THEN<statement>
ELSE<line number>(
,~OTO<line number>: (ELSE<statement> ~
I

....

where the condition is defined as one of the following:

<relational expression> <logical operator> <relational expression>
and a relational expression is defined as:

<expression> <relational operator> <expression>
as described in section 3.5.

The specified condition is tested and if

9-8

it is true the THEN/GOTO part of the statement is executed.

If the

condition is false, then the ELSE part of the statement is executed.
Following the word ELSE can be either a statement to be executed or a
line number to which control is transferred.
The IF-THEN-ELSE statement can appear anywhere in a multiple
statement line.

As an example of an IF-THEN-ELSE statement:

75 IF X>Y THEN PRINT "GREATER" ELSE PRINT "NOT GREATER"
Since any statement can follow either the THEN or ELSE in the above
statement, it is possible to nest IF statements to any desired level.
For example:
lJJ

IF A>B THEN IF B>C

THEN PRINT "A>B>C"

The message A>B>C is printed only if the two conditions .;&~cified are
both true.
lJJ

An equivalent statement could be expressed as follows:
IF A>B

AND B>C THEN PRINT "A>B>C"

To further clarify the relationship between the quantities A, B,
and C, the following statement could be used:
lJJ

IF A>B THEN IF B>C THEN PRINT "A>B>C"
ELSE IF A>C THEN PRINT "A>C>B"

(Notice the use of the LINE FEED character to continue the statement
on a second line.)

There are two ways in which the above statement

could be interpreted.

One in which the ELSE clause is attached to the

test A>B and one in which it is attached to the test B>C.

In order to

resolve such situations, BASIC-Plus uses the following rule:
An ELSE clause is always associated with the nearest
unmatched IF-THEN to its LEFT.
Thus in the above statement the ELSE clause is executed only if the
B>C test is false.

If the A>B test had been false, execution would

have immediately proceeded to the next statement and nothing else in
statement 100 would be executed or tested.
If any clause within a complex IF statement is satisfied, then
execution proceeds to the seaLenzenL immediately following the IF
I,' VI-<-

,u...r

9-9

statement.

"fIti!! i.s ei1!aer 'Sse :RQxt b; ghar pum}ge;rQQ lii'SatQmeR1! er "1!Ae

~ight 9~J ~ co1on L:) on the same physical line as the
~ ;.u ik.,,,,, tIu... ,sclpt af- tfI.L-rHEJJ or ~ .. fi..S£' "
statement~
It should be noted that several physical lines can be

statement to the
IF

included in one logical line by use of the line feed character.
The reader is invited to consider the following program!
LISTNH
1.0 INPUT A,B,C
2f1 IF A>B THEN
IF B>C THEN PRINT "A>B>C"
ELSE IF C>A
THEN PRINT "C>A>B"
ELSE PRINT "A>C>B i/
ELSE IF A>C THEN PRINT "B>A>C"
ELSE IF B>C
THEN PRINT "B>C>A"
ELSE PRINT "C>B>A"
READY
RUNNH

? 3,6,1
B>A>C
READY
RUNNH
? 2,9,21
C>B>A
READY

The use of the line feed and tab characters greatly improves the
legibility of complex program statements such as line 20 above.
9.6

CONDITIONAL TERMINATION OF FOR LOOPS
In the simple FOR-NEXT loop described in section 3.6.1, the

format of the FOR statement is given as:

line number

(
FOR<variable>=<expression>TO<expression~STEP<expression~.

There are many situations in which the final value of the loop variable
is not known in advance and what is really desired is to execute the
loop as many times as necessary to satisfy some condition.

In evaluat-

ing a function, for example, this condition might be the point at
which further iterations contribute no further accuracy to the result.
BASIC-Plus provides a convenient way of specifying that a loop is to
be executed until a certain condition is detected or while some
condition is true.

These statements take the forms:

9-10

line number

FOR<variable>=<expression>~TEP<expression~WHILE<condition>

and

line number

FOR<variable>=<expression~TEP<expression~TIL<condition>

The condition has the same structure as specified in an IF statement
(see section 3.5) and can be just as elaborate, if necessary.

Before

the loop is executed and at each loop iteration the condition is tested.
The iteration proceeds if the result is true

(FOR-WHILE) or false

(FOR-UNTIL) .
The difference between a FOR loop specified with a WHILE or UNTIL
and one specified with a terminal value for the loop variable is worth
noting, in order to avoid potential pitfalls in the usage of each.
Consider first the two loops below:
1.0 FOR I = 1 TO 1.0
11 PRINT Ii
12 NEXT I
and
2.0 FOR I = 1 UNTIL 1>1.0
21 PRINT Ii
22 NEXT I
Each of these loops prints the numbers from 1 to 10.

When the loop at

line 10 is done, however, the loop variable is set to the last value
used (that is, 10)-.

In the second loop beginning at line 20, the loop

variable is set to the value which caused the loop to be terminated
(that is, 11).
Next consider the two loops following:
LISTNH
1.0 X=l.0
2.0 FOR 1=1 TO X
3.0 X=X/2
4~ PRINT {,X
5.0 NEXT I
1.0.0 X=l.0
11.0 FOR 1=1 UNTIL I>X
12.0 X=X/2
13.0 PRINT I,X
14.0 NEXT I
(Cont. next page)

9-11

RUNNH
1

5
2.5
1.25
.625
.3125
.15625

2
3

4
5
6
7
8

.~78125

.p390625
.p1953125
.9765625E-2
5
2.5

9
l~

2
READY

In the case of the loop beginning with line 20, the iteration stops
when I exceeds the initial value of X (that is, 10).

Even though

the value of X changes within the loop, the initial value of X
determines the performance of the loop.

In the second loop, the

current value of X determines when the iteration ceases.

Thus, after

three iterations,I is greater than X in the second loop and the loop
is terminated.
1.)

(The STEP value when omitted, is still assumed to be

These forms of loop control are particularly useful in iterative
applications where data generated during the loop execution determines
loop completion.
Consider the problem of scanning a table of values until two
successive elements are both 0, or the end of the table is reached.
l~
2~

9.7

FOR I = 1 UNTIL I=N OR X(I)=~ AND X(I+l)=~
NEXT I

STATEMENT MODIFIERS
To increase the flexibility and ease of expression within

BASIC-Plus, five statement modifiers are available (IF, UNLESS, FOR,
WHILE, and UNTIL).

These modifiers are appended to program state-

ments to indicate conditional execution of the statements or the
creation of implied FOR loops.
9.7.1

The IF Statement Modifier
The form:

9-12

is analogous to the form:
IF<aondition>THEN<statement>
For example:
l~

PRINT X IF X<>~

is the same as:
l~

IF X<>~ THEN PRINT X

The statement is executed only if the condition is true.
When a statement modifier appears to the right of an
statement, then the modifier operates only on the

IF-THEN

THEN clause or the

ELSE clause, depending on its placement to the left or right of
ELSE. For example:
l~~

IF 1=1 THEN PRINT "HELLO" ELSE PRINT "BYE" IF

l=~

will print
HELLO

is true. The modifier IF l=~ is false, but as
it applies only to the ELSE clause, it is never tested.
since the test

1=1

It is not possible to include an
modifier form of

ELSE

clause when using the

IF.

Several modifiers may be used within the same statement.

For

example:
l~~

PRINT X(I,J) IF I=J IF

X(I,J)<>~

which will print the value of X(I,J) only if the value of (I,J) is
non-zero and if I equals J.

Whenever there is

more than one modifier

on a line, the modifiers are executed in a right-to-left order.

is, the rightmost one is executed first, and the leftmost one is
executed last. This situation is described by the term "nested
modifiers".
9-13

That

An additional operational advantage of this interpretation of
IF
9.7.2

modifiers is illustrated in the discussion of

FOR modifiers below.

The UNLESS Statement Modifier
The form:
<statement> UNLESS <condition>

causes the statement to be executed only if the condition is false.
For example, the following statements are all equivalent:
l~

PRINT A UNLESS

PRINT A IF NOT A=~

IF NOT A=~ THEN PRINT A

IF A<>~ THEN PRINT A

A=~

This particular form simplifies the negation of a logical condition.
9.7.3

The FOR Statement Modifier
The form:

<statement> FOR <vapiabZe>=<fopmuZa>TO <fopmuZa> STEP
can be used to imply a FOR loop on a single line.
l~

PRINT I, SQR(I) FOR 1=1 TO

This statement is equivalent to the

For example:

follow~ng

FOR-NEXT loop:

l~ FOR I = 1 TO l~
11 PRINT I, SQR(I)
12 NEXT I

In cases where the FOR-NEXT loop is extremely simple, the necessity
for both a FOR and a NEXT statement is eliminated.

Notice that this

implied FOR loop will only modify (and hence execute iteratively)
one statement in the program.

Any number of implied FOR loops can be

used in a single program.
As is the case with all modifiers, a FOR modifier in an IF
statement will operate only on the THEN or ELSE clause with which it
is associated, and never on the conditional expression to the left of

9-14

the THEN.

Thus, if it was desired to print all non-zero values in a

matrix x, dimensioned to be 100 elements long, the following program:
l~ DIM X(l~~)
15 READ XCI) FOR 1=1 TO l~~
2~ IF X(I)<>~ THEN PRINT I,X(I) FOR 1=1 TO

l~~

will not operate properly, since the implied FOR loop at line 20
applies only to the THEN PRINT .•.
the

IF ...

part.

part of the statement, and not to

Thus, the first value of X tested is X(lOO), since

I remained at 100 from statement 15.
it is only necessary to state line
rather as a
2~

PRINT statement

To achieve the desired effect,

2~,

not as an

statement, but

with nested modifiers; for example:

PRINT I,X(I) IF X(I)<>~ FOR 1=1 TO

l~~

when expressed in the latter form, the nested modifier rule takes
effect, and all values of XCI) are tested and printed as appropriate.
9.7.4

The WHILE Statement Modifier
The form:
<statement> WHILE <condition>

is used to repeatedly execute the statement while the specified condition is true.
l~

For example:

LET X=xt2 WHILE Xf2<lE6

is equivalent to:
l~ LET X=Xt2
11 IF X<lE6 THEN

The WHILE modifier (and the UNTIL modifier below) will operate usefully
only in iterative loops where the logical loop structure modifies the
values which determine loop termination.

This is a significant

departure from FOR loops, in which the control variable is automatically iterated; a WHILE statement need not have a formal control
variable.

The following statements will never terminate properly;

such programs are sometimes called "infinite loops":
l~
2~

X=X+I WHILE I<l~~~
PRINT I, A(I) WHILE A(I)<>~

9-15

In both cases, the program fails to alter the values which are used to
determine when the loop is done.
Successful applications of the WHILE

modifier include the follow-

ing:
5
l~
2~

9.7.5

!TEST OF SQUARE ROOT ROUTINE
X=X+l WHILE X=SQR(Xt2)
PRINT X

The UNTIL Statement Modifier
The form:
<statement> UNTIL <condition>

is used to repeatedly execute the statement until the statement becomes true; which is to say, while the statement is false. For example:
l~

X=X+l UNTIL X<>SQR(Xt2)

is the same as

1.0 X=X+l
2~

9.7.6

IF X=SQR(Xt2) THEN

Multiple Statement Modifiers
More than one modifier can be used in a single statement.

modifiers are processed from right to left.
l~

LET A=B IF A>~ IF

B>~

which is equivalent to:
l~

IF B>~ THEN IF A>~ THEN A=B

IF B>~ AND A>~ THEN LET A=B

l~
2~
3~

IF B=~ THEN
IF A=~
LET A=B

or
4~

9-16

For example:

Multiple

A two dimensional matrix (m by n) can be read a row at a time as
follows:
75

READ A(I,J) FOR J=l TO M FOR 1=1 TO N

which is equivalent to:
75

MAT READ A(M,N)

and to:
1.0 FOR 1=1 TO M
2.0 FOR J=l TO N
3.0 READ A (I ,J)
4.0 NEXT J
5.0 NEXT I
Also see section 9.8.3, interaction of FOR and IF.
9.8

ADDITIONAL PRINT STATEMENT FEATURES

9.8.1

PRINT-USING Statement
If elaborate formatting is required for an output operation, the

PRINT-USING statement is available.
"line number

The statement is of the form:

PRINTf#<expreSSion>,3 USING<string>, < "lis t>

If the expression is omitted, the output is assumed to be directed
to the terminal.

The string can be either a string constant or a

string variable and is interpreted as an exact image of the line to
be printed, using the following notation:"
a.

An exclamation point (!) identifies a one character string
field.
The string is specified in the <list> part of the
PRINT statement. For example:
1.0 PRINT USING "!!!", "AB", "CD", "EF"
causes
ACE
to be printed. The first character from each of the
three string constants or variables is printed.
Any other characters beyond the first are ignored.

~first

A character string field of two or more characters is
indicated by spaces enclosed between backslashed. The
backs lash character is produced by typing SHIFT/L on

9-17

the keyboard.
If zero spaces are enclosed, a field two
columns wide is assumed, one space indicates a field
three columns wide, etc. For example:
2~ PRINT USING "\ \ \
causes:

\", "ABeD", "EFGHI"

ABEFGH
to be printed. The first two backslashes have no spaces
enclosed, hence permit the printing of two characters (AB).
The second two backslashes enclose two spaces and hence
permit the printing of four characters (EFGH). Notice
that no spaces are printed unless they are specifically
planned.
c.

Numeric fields are indicated with the # character. Any
decimal point position can be specified and rounding is
performed as necessary (not truncation). For example:
l~

PRINT USING "###.##", 12.345

will cause:
12.34
to be printed, while:
l~

PRINT USING "####.", 12.345

causes:
12.
to be printed. Numeric fields are right justified; that
is, if a number does not fill the allotted spaces leading blanks precede the number. Where the field specified
is too small for a constant or variable to be printed,
the * character is used to fill the field. For example:
l~

PRINT USING "##",

l~~

causes:

**
to be printed.
d.

When the exponential form of a number is desired, the
numeric field is followed by the string tttt (four t
characters) •
This suffix allocates space in the
line for E ±xx. Any arrangement of decimal points
is possible. For example:
5
l~
2~

F$="##tttt
###### ## #"
A=lE4
PRINT USING F$,A, A, A, A

prints the following:
lE+~4

Thus, in order to print the line:
A=1.23

B=2.45

where A=1.23111 and B=2.45457, format control can be
used as in the following line:
l~
2~

LET F$="A=##.## B=##.##"
PRINT USING F$, A,B

9-18

Notice that when the PRINT-USING statement is used,
the usual PRINT statement punctuation characters
(commas and semicolons) have no effect.

The PRINT USING statement is generally employed where a large
amount of data is to be formatted for output in a particularly uniform
manner.
9.8.2

PRINT Functions
In order to aid in formatting simple and complex PRINT statements,

the following functions are provided:
Function

Meaning

POSen)

Returns the current position of the print head
(imaginary for disk files) where n is the I/O
channel number.
POS(~) returns the value for
the user's terminal.

TAB (x)

Tab to position x in the print record.
For
example, the Teletype paper has 72 printable
columns.
TAB(4) causes a movement of the
print head to column 4 regardless of whether
the print head is currently before or after
print position 4.
(If currently past position
4, position 4 of the next line will be selected.

CHR$ (x)

Output the single ASCII character corresponding
to the number x.

For example:
l~

PRINT "X" jTAB (1.0) jCHR$ (65)

causes the following to be printed:
X

, ,~'--y---'"
't'
Ifl
r
pos~ ~on
p

pos~t~on 1

8 spaces
Other character string functions for use with the PRINT
statement (or any other statement) are described in the section on
Character String Functions, section 5.5.

9-19

9.9

INPUT LINE STATEMENT
The INPUT LINE statement causes the input of a string of charac-

ters (either from a specified file or the terminal-) from the beginning
of one line up to the LINE FEED character to be read into the string
variable specified.

line number

The statement is of the form:
INPUT

LINE[#<expression>~<string variable>

Where the input is to be from the Teletype no expression is used to
indicate the source of the input.

For example:

75 INPUT LINE A$
causes the system to pause while the user types a line of input (on
the terminal up to 72 characters) followed by the RETURN key.

The

RETURN key generates a carriage return/line feed, which is appended
to the other data typed by the user.

Thus, every character typed

(including such characters as space and quote) is passed to the
program, which can analyze the data using the normal string manipulation functions.

This is different from the normal mode of inputting

strings, since ",', and <space> are normally disregarded, although
not here.

For example:
l~
2~

INPUT LINE A$: PRINT "LINE:" A$;
INPUT A$: PRINT "STRING:"; A$
3}1 GOTO 1}1
? ABCD
LINE:ABCD
? ABCD
STRING:ABCD
? ABC D
LINE: ABC D
? ABC D
STRING:ABCD
?I!ABCDI!
LINE: " ABCD"
? "ABCDI!
STRING:ABCD

tc
READY
9~ OPEN"DTA4:DATA" FOR INPUT AS FILE
95 INPUT LINE #4, B$

causes the input of a line of data from the file DATA on DECtape unit
4 through I/O channel 4.

9-20

9.10

SYSTEM FUNCTIONS
RSTS-ll has several system functions which allow the user to

obtain certain information about or perform operations with the
system.

The functions are described in Table

9.2

Table 9.2
SYSTEM FUNCTIONS
Meaning

Function
DATE$(~)

Sample Usage

returns the current day, month,
2: :
i ... the form:
2-MAR-7l 111)1)1:

returns a character string
corresponding to the Julian
date N+70,000
DATE $ (1) = "~1-JAN-7~"

155 PRINT X%(I) ,DATE$(I)

DATE$(~)

-w A year j

DATE$ (N)

DATE$(24~)

"~5-MAY-7~"

TIME$ (fI)

returns the current time of
day as a character string as
follows:
TIME$(.0) = "~5:3.0 PM"

75 IF TIME$(~) 2:"~5:45 PM"
PRINT "TIME- TO QUIT"

TIME$(N)

returns a string corresponding
to the time at N minutes before
midnight, for example:
TlME$(l) = "11:59 PM"
TlME$(144~) = "12:~~ AM"
TlME$(72l) = "11:59 AM"

1.0 PRINT #4,TIME$(I) ,I

TIME (J;n

returns the clock time in
se~onds since midnight.

IF TIME(~»432~.0
THEN PRINT "AFTERNOON"

TIME (1)

returns the central processor
(CPU) time used for this job
in ~.l second quanta.

IF TIME(1»3~
THEN STOP

TIME (2)

returns the connect time (time
during which the user has been
logged into the system) for this
job in minutes~

IF TIME(2»18~~
THEN STOP

SLEEP (X)

this function is used as a state- 75
ment and causes the currently
running program to be dismissed
until either X seconds have elapsed
or a line is typed at the user's
terminal, whichever comes first.
No error is generated if input
is not received.

9-21

SLEEP

(l~)

Table 9.2 (Cont.)
Function

Meaning

WAIT (X)

this function is used as a
statement and has no
immediate effect. Failure
to supply input on a terminal within X seconds after
an INPUT statement is
executed will result in
the generation of error condition #15.

causes the system to wait as
long as necessary for input
from the terminal.

WAIT (feJ)

Sample Usage

9-22

45
5~
l~~

ON ERROR GOTO l~~
WAIT{15Y
INPUT "ANSWER";X
IF ERR=15 THEN RESUME

WAIT(~)

CHAPTER 10
BASIC-PLUS INPUT AND OUTPUT OPERATIONS

10.1

READ AND DATA STATEMENTS
A READ statement is used to assign to a list of variables values

obtairted from a data pool composed of one or more DATA statements.
The two statements are of the form:

line number
line number

READ <list of variables>
DATA <list of values>

The list of variables can include floating point, integer, subscripted, or character string variables.

The list of values must

correspond in type with the variables to which the value will be
assigned (the exception is that integer and floating point values
are interchangeable, although they are stored according to the type
of the variable) .
The data pool consists of all DATA statements in a program.
Values are read starting with the DATA statement having the lowest
line number and continuing to the next lowest, etc.

The location of

DATA statements in a program is irrelevant, although for simplicity
they are usually kept toward the end of the program.

(The DATA

statements must occur in the proper numeric sequence, however.)

DATA statement must be the only statement on a line, although a READ
statement can occur anywhere on a line.
If a READ statement is out of data, an error message is printed
and program execution is terminated.

(This error can be treated

through the ON ERROR GOTO statement, section 9.4.)
Quotes are necessary in DATA statements only around string items
which contain a comma or where embedded blanks within the string are
significant.
Matrices are read from DATA statements via the MAT READ statement
of the form:

line number

MAT READ <list of matrices>

10-1

This reads the value of each element of a predimensioned matrix from
the data pool.

Each element in the list of matrices indicates the

maximum dimension of the matrix to be read (which cannot be greater
than the dimensioned size of the matrix).
separated by commas.
l~
2~

Individual elements are

For example:

DIM A(2~,2~), B(5~)
MAT READ A, B(35)

The above lines read values for the 20 x 20 matrix A and 35 out of
the possible 50 values for the B matrix (remaining elements are zero).
Data is read in row by row; that is, the second subscript varies most
rapidly.
10.2

RESTORE STATEMENT
The RESTORE statement reinitializes the data pool of the program's

DATA statements.

This makes it possible to recycle through the DATA

statements beginning with the lowest numbered DATA statement.

The

RESTORE statement is of the form:

Zine number

RESTORE

For example:
85

RESTORE

causes the next READ statement following line 85 to begin reading data
from the first DATA statement in the program, regardless of where the
last data value was found.

See section 3.9 for an example program

using the RESTORE statement.
The RESTORE statement can be placed in any position on a multiple
statement line.
10.3

INPUT STATEMENT
The INPUT statement allows data to be entered to a running

program from an external device, the user's keyboard, disk, DECtape,
paper tape reader, etc.

Zine number

The full form for this statement is:

INPUTf#<expression>} <variable list>
~

10-2

In many cases the simpler form:

line number
is used.

INPUT <variable list>

This last form causes a ? to be printed at the terminal and

the system then waits for the user to respond with the appropriate
values.

If sufficient values are not typed, the system prints

another ?; if too many values are typed, excess values are ignored.
~"'--;.-..~~-,-

.... -,'-.... ,.-~""'.---

_...

"'----"'----,..."

.. ..."""... ..
."....,

,..--

.-~

This last form also allows the user to intersperse strings to be
printed between the variables to be input.
l~

For example:

INPUT "YOUR NAME IS";N$, "AGE"; A

when executed would allow the following interaction at the terminal
(the underlined characters are typed by the user):
YOUR NAME IS? JEAN
AGE? 23
The format:

line number

INPUT #<expression>, <variable list>

causes input to be read from the file or device indicated in the
expression by the number it was given when it was opened.

(See

section 7.2 or 10.5 for a description of the OPEN statement.)

the value of the expression is non-zero and the specified file is
open as using the Teletype as an input device, then no
is printed at the terminal when input is requested.

? character

For example:

75 OPEN "TTY:" FOR INPUT AS FILE 2
8~ INPUT #2, A
The system then pauses while the user types a numeric value for the
variable A, although no prompting ? or character string message is or
can be printed on the terminal.
Another format of the INPUT statement allows for the entering of
an entire line of data as a single character string entity, regardless
of embedded spaces or punctuation.

line number

This format is:

INPUT LINE f#<expression> ~<s tring variab le>

10-3

For example:
25

INPUT LINE A$

would pause and allow the user to enter characters on the terminal
The end of the line being input is the carriage return/

keyboard.

line feed sequence.
2~

As another example:

OPEN "DSK:F2" FOR INPUT AS FILE 7
INPUT LINE #7, B$

These lines cause the system to open a file F2 on the system disk on
channel 7 (of 12 possible channels) to input a line of characters
up to the next LINE FEED character.

(See Table 7-1 for the size

of buffers available for each device.)
The MAT INPUT statement is used to input the values of a predimensioned matrix from a specified input device.

Where no particular

device is specified, the input is accepted from the user terminal.
For example:
2~~

MAT INPUT

A(2~)

causes 20 floating point values to be accepted as elements of the
matrix A.

A statement of the form:

line number

MAT INPUT[#<expression>~<variable list>

causes the input to be read from a file or device indicated by the
expression and previously opened.
45
5~

DIM B(1~,25)
OPEN"DTA2:DTAl" FOR INPUT AS FILE 1
MAT INPUT #1, B(1~,25)

The above lines cause the file DATAl on DECtape 2 to be open for
input on channel 1 (of 12 possible channels) and a matrix of values
for the elements of B to be read to fill B(10,25).
elements are not assigned a value.

The zero

Where input is from the user

terminal a ? is printed; however, reference to another device does
not cause the printing of the prompting character.

Depending upon

the name of the matrix, the MAT INPUT statement allows input of
floating point, integer, or character string values.
10-4

10.4

PRINT STATEMENT
In its simplest form, the PRINT statement looks as follows:

line number PRINT
This causes a carriage return/line feed to be performed on the user
terminal.

The format:

line number PRINT <list>
causes the printing of the elements in the list on the user terminal.
An element in the list can be any legal expressioni where an element

is not a simple variable or constant, it is evaluated before a final
value is printed.

The list can also contain a character string between

quotes which will be printed exactly as it appears.
NOTE
If a character string is enclosed in a PRINT statement with an initial quote and no terminating quote,
the terminating quote is considered to be the end
of that PRINT statement. For example:
If.J PRINT "NAME IS A$
If.J PRINT "NAME IS A$"
2f.J PRINT "NAME IS" A$
Line If.J is shown in two equivalent forms. Line 2f.J
is the correct form to generate the printed line:
NAME IS JOHN DOE
where A$ = "JOHN DOE".
Elements in the list are separated by commas or semicolons.

For

example:
If.J
15

A=l: B=2: C=3
PRINT Ai A+B+C, C-A, "END"

when executed, will cause the following line to be printed:

END

A terminal line is considered to be divided into five print zones
of fourteen spaces each.

Use of these zones involves the

comma character which causes the print head to move to the next
available print zone (from 1 to 14 spaces away).

If the fifth print

zone on a line is filled, the print head moves to the first print
zone on the next line.
10-5

The semicolon character functions as follows:
a.

if a variable, function, or expression is followed by
a semicolon, the value is printed with a preceding
minus sign if the number is negative, or a space if
it is positive. The number is then followed by a
single space.

formatted character strings (explained later) followed
by a semicolon, are printed with no preceding or
trailing spaces, except as explained in (a) above.

Any PRINT statement which does not end with a semicolon or comma
character causes a skip to the next line after printing the elements
in the list.

The presence of the punctuation character causes the

next PRINT statement to continue on the same line under the conditions
already defined.
In general, the output rules for the PRINT statement include:
a.

suppression of leading and trailing zeros to the right
of a decimal point. Where a number is an integer, printing of the decimal point is also suppressed.

at most seven significant digits are printed.

most numbers are printed in decimal format unless the
user indicates otherwise. Numbers too large or too
small to be printed in decimal format are printed in
exponential format.

character string constants are printed without leading
or trailing spaces.

extra commas cause print zones to be skipped.

semicolons separating character string constants from
other list items are optional; if used, their
significance is as already defined; if not used, no
extra spaces separate the character string from the
value to be printed.

Output can be directed to a device other than the Teletype with
the following command:

line number

PRINT #<expression>3<list>

Where the expression is the number of a previously opened output file,
out of the 12 possible opened files
l~
5~

(see section 10.5).

OPEN "PTP:" FOR OUTPUT AS FILE 3
PRINT #3, B, D, A+7, FNX(B)

10-6

For example:

causes four values to be punched onto paper tape by the high speed
punch which is opened for output as file 3 out of the possible 12
files.
In order to perform formatted output, the following statement is
used:

Zine number
where the expression

#<expression>~

USING

<string>~

<Zist>

(which is optional) indicates the file or device

which is the destination of the output; the string is either a string
constant or a string variable which is an exact image of the line to
be printed; and the list is a list of items to be printed.

The

string constant is constructed according to the following rules:
a.

an exclamation point identifies a one character string
field.
The string is specified in the list within the
PRINT statement. For example:
l~

PRINT USING "!!!", "AB", "CD", "DE"

which causes:
ACE
to be printed at the user's terminal.
b.

a variable string field of two or more characters is
indicated by spaces enclosed between backslashes.
The backslash character (\) is produced by typing
SHIFT/L on the keyboard. Enclosing no spaces indicates
a field two columns wide, one space is equivalent to
three columns wide, etc.
2~ PRINT USING" \ \ \

\", "ABCD", "EFGHI"

causes
ABEFGH
to be printed at the user's terminal.
c.

numeric fields are indicated with the # character.
Any decimal point arrangement can be specified,
rounding is performed as necessary. For example:
3~

PRINT USING "###.##", 12.345

causes
12.36
to be printed on the user's terminal
4~
5~

PRINT USING "####", 12.345
PRINT USING "####.", 12.345
PRINT USING "##", l~~

10-7

cause
12
12.

**
to be printed on the user's terminal.
d.

when the exponential form of a number is desired, the
numeric field is followed by the string tttt which
allocates space for E±~~. Again, any arrangement of
decimal points is permitted. For example:
5

F$= "##tttt ####..

A=l~~~~.

## #"

PRINT USING F$, A,A,A,A

causes
lE+~4

to be printed at the user's terminal.
As another example:
5
l~
2~
3~

LET A=1.32111: B=2.45457
LET F$=" A=##.## B=##.##"
OPEN "LPT:" FOR OUTPUT AS FILE 4
PRINT #4, USING F$, A,B

would cause:
A= 1.32

B= 2.45

to be printed on the line printer.

Notice that when the PRINT USING

statement is used, commas and semicolons have no effect on the output
formatting.
The MAT PRINT statement allows for easy printing of a predimensioned matrix or matrices.

Zine number

The statement is of the form:
MAT PRINT #<Zist of matrices>,

For example:
15
25

DIM A(16), B8(5,lO);C%(32),El(32)
MAT PRINT A(15), B$ (3, 7), C% (32), El

If the elements of the list of matrices are the unsubscripted names
of the matrices, the entire matrix is printed.

If the elements are

subscripted, then the subscript indicates the maximum size of the
matrix to be printed.

The matrix name can be followed by a semicolon to indicate that
the values are to be printed in a packed fashion, or by a comma to
indicate that each element is printed in its own zone.
5

12,0
13,0

DIM A(l,0,l,0) ,B(l~,2~)
MAT PRINT A:
MAT PRINT B(l~,l,0)

!MATRIX A IS PRINTED IN PACKED FORMAT
!1~*1,0 MATRIX PRINTED, 5 VALUES PER
! LINE

Rowand column matrices can also be printed.
5
5~
6~

For example:

DIM A ( 5), B ( l~)
MAT PRINT A;
MAT PRINT B

Line 50 causes A to be printed as a row matrix, closely packed; line
60 causes B to be printed as a column matrix.
7~

The form:

MAT PRINT A,

would cause the matrix A to be printed as a row matrix, five values
per line.
10.5

OPEN STATEMENT
The OPEN statement has two formats:
:,.
<str ~ng> FORrINPUT
-.9UTPUT ~

AS FILE<expression>

line number

OPEN

line number

OPEN <string> AS FILE <expression>

The first form is used to open files for input or output of variables
through use of INPUT and PRINT statements.

The second form is

generally used to open files for input and output of virtual core
matrices through the MAT INPUT and MAT PRINT statements.
The string in the OPEN statement is either a character string
constant or variable and represents the device on which a file is
to be opened.

In the case of a disk or DECtape file, the name of the

file is also indicated.

The various device names are as follows:

10-9

~~t¥- ~II(~~ V\

rrf",:
DF: ~
i1f~ : ~: to~7:
Pe: .~
1'P: ~
LP: ~

high-speed paper tape reader

Gil: ~:

card reader

system disk
DECtape units 0 to 7
high-speed paper tape punch
line printer

MSR:

mark sense card reader

~&:: ....

user terminal

116 Vl : ~

terminal n within the system
system library

Examples of acceptable character strings are shown below:
"DSK:FOO"

specifies the file Faa on the system disk

"DTA4:MMM:

specifies the file MMM on DECtape unit 4

"PTP:"

specifies the high-speed punch

"PTP:FOO"

specifies the high-speed punch, Faa is
ignored

"Faa"

specifies the file Faa on the system disk,
equivalent to DSK:FOO (disk is the default
storage device)

"DSK:FOO.TMP"

specifies the file Faa on the system disk
with the extension.TMP

The expression in the OPEN statement is the internal file
designator, an integer number (constant or variable) between 1 and
12.

Internal file designator

is always open and is equivalent to

referencing the user's terminal.
For example:
l~

OPEN "PTP:" FOR OUTPUT AS FILE 3
PRINT #3, "BEGINNING OF DATA FILE"

The above sequence opens the high-speed punch for output on internal
file designator 3 which is then used in a PRINT statement to cause
BEGINNING OF DATA FILE to be punched in ASCII code on the paper tape.
The paper tape punch can only be opened for output, a message is
printed if an attempt is made to open that device for input.
l~

11
12

LET I$ = "LPT:": E=l
OPEN I$ FOR OUTPUT AS FILE E
PRINT #E, A,SQR(A) FOR A=l TO

10-10

The above sequence uses variable names in the OPEN statement rather
than constants and causes a table to be printed on the line printer.
IfJ
11

OPEN "DTA2:REM.DTA" FOR INPUT AS FILE 1
INPUT #1, A, D4, B$, C%

The above sequence opens the file REM with the extension .DAT for
input on internal file designator 1 and then accepts as input four
values.
When input is accepted from the user terminal, a ? is printed
prior to the acceptance of data input by the system.
request input without the prompting character

In order to

(which is frequently

useful as a grammatical device), the user terminal (TTY:) can be
opened on some internal file designation other

than~.

only generated for input requests on internal file #.0'.)
1.0'
11
12

(The? is
For example:

OPEN "TTY:" AS FILE 1
PRINT "TYPE YOUR NAME"
INPUT #1, A$

results in the following sequence:
TYPE YOUR NAME
JOHN DOE

When using the

line number

OPEN <string> AS FILE <expression>

form, a normal data file can be opened for input and output or, more
often, the statement is used to indicate the presence of a virtual
data matrix on the system disk.

This virtual data storage facility

allows the user to individually address and update elements within a
disk file in a random (non-sequential) manner and allows the user to
address more data storage area than is available in core at
installation.

j:\e(~d 1 VI""

The OPEN statement is used I-ol19uill!, a DIM statement

defining the virtual data matrix.

line number

The DIM statement is of the form:

DIM #<expression>,<list>

For example:
1.0'
11

~he

OPEN "DATAl" AS FILE #1
DIM #1, A (lfJfJ.0', 12.0'.0') , B$(lfJfJfJ), C%(5fJfJ)
10-11

The OPEN statement gives the name of the file as DATAl on the system
disk. (only the disk can be used for virtual core storage).

The

internal file number associated with that particular disk file is 1.
The matrices A, B$, and C% are then defined as virtual matrices
referenced through internal file designator 1.
Floating point numbers, integers, and strings can all reside in
virtual core matrices.

More than one matrix can be specified in one

virtual core file, as shown above.
String matrices, which is to say string variables, are handled
slightly differently in virtual storage than when stored in core.
In core matrices are of variable length from ~ to any arbitrary
length.

Strings in virtual core are of fixed length.

All elements

of a given matrix have the same length (even though all or part of any
number of elements can be blank) .
The length of virtual core matrices, then, varies from 1 character to 512 characters.

Although any length can be specified, the

system forces lengths to be a power of two.

That is, the actual length

of a string matrix element in virtual core is one of the following:
1, 2, 4, 8, 16, 32, 64, 128, 256, 512
When the user indicates a value other than one of the above, the next
higher value is automatically assigned.
l~
l~

DIM #1,
DIM #1,

X$(l~)
X$(l~)

For example:

65
128

the two lines above are exactly the same in function.
is specified in the DIM statement, as shown above.
15

DIM #1,

A$(l~~)

32,

B$(l~~)

The length
For example:

C$(l.3~)

defines three virtual core matrices which can later be referenced in
a program wpere
A$ consists of 101 strings of 32 characters each;
B$ consists of 101 strings of 4 characters each;
C$ consists of 101 strings of 16 characters each.

10-12

Ea&~ frf)'Yfo-'1 a-cc,S's-w., a f~i.~f¥ vir1lA( ~ {r-/e IM-uJt k~ ~ (~J. CKfy~ )
PIn
~t~1(~t JpSCI;-~ flu, ~~;l~t,~ J /-t)t t,lt.
In order for the user to reference any element in a virtual core
matrix, the matrix must be defined and associated with some internal
file designator, as follows:
l~

OPEN "FOO" AS FILE 1
DIM #1, A(l~~~), B(l~~),

C$(5~~)=256

MAT INPUT and MAT PRINT statements as well as a statement of the form:
255

INPUT #1, A(255)

can then be used referencing the predefined matrices.

Any element in

#Jc.)l
~("'J~ IG
~{iv;J(i v-(~cl L
/.7 Ie.. -t r<k-&iu tl~

virtual core can be addressed independently of the remaining elements
of that matrix.
In general, the action of the two different types of OPEN statement can be summarized as follows:
2~
3~

OPEN "FOO" FOR INPUT AS FILE 1
OPEN "FEE" FOR OUTPUT AS FILE 2

In the above statements, if a file being opened for input does not
exist, an error message is returned.

If a file being opened for

output does not exist, it is created.

If a file for output already

exists and is not write-protected, it is deleted and recreated.
4~

OPEN "FII" AS FILE 3

If FII already exists as a file

(on the system disk, in this case),

then the existing file is used; if there is no file names FII, one is
created.

(Other devices than the system disk can be specified for

this format.

However, virtual core matrices can only be referenced

on system disk files.
the rules specified.)
10.6

Other devices can be referenced for I/O under

Vvtv~ ~ C;t~ ~,t lac. .t.4/ ~ Glla;" I

CLOSE STATEMENT
The CLOSE statement is used to terminate I/O to or from a

device, removing the internal file designation.

Once a file has

been closed, it can be reopened at any time for I/O on any internal
file designator.
program execution.

All files are automatically closed at the end of
The format of the CLOSE statement is as follows:

10-13

line number

where the expression is the internal file designator.
file can be closed with one CLOSE statement.

More than one

Closing a file before

the end of program execution has the advantage of freeing more core
storage space to open other files.

An example of the CLOSE statement

follows:
25
31J

CLOSE
CLOSE

4
1,

10-14

PART III

USING RSTS-II

This section deals with the interaction between the user
and the RSTS-II terminal, how to enter and edit user programs,
and how to give commands to BASIC-Plus.
Clearly, the listing, running, saving, or compiling of
a program differ in kind from the individual statements composing the program.
operation.

System commands perform this type of

Other operations include assigning of peripheral

devices for program input and/or output, the determining of
the length of the current program or number of user files
available, renaming and replacing of current files, and the
enabling and disabling of the echo feature on the RSTS-II
terminal.
A system command can be given at any point after the
system has printed READY and before the user issues a RUN
command.

CHAPTER 11
BASIC-PLUS SYSTEM COMMANDS

11.1

ON-LINE WITH BASIC-PLUS

11.1.1

Project-Programmer Numbers and Passwords

Before the user attempts to use the RSTS-ll system, the system
manager or an instructor will assign him both a unique projectprogrammer number and a password.

The project-programmer number

might, for example, look as follows:
100,101
The number 100 above is the project number (possibly held by a group
of people having a common interest); and the number 101 above is the
programmer number (held by only one person within the project group) .
Thus, each individual's project-programmer number is different.
This allows the assignment of protection codes to user files for
various relationships among users (see section 7.7 describing the
NAME-AS statement).
The user is also assigned a password.

This password is an

alphanumeric code particularly assigned to an individual user.

This

password is never printed on the terminal and, hence, allows for a
measure of security in limiting the use of the computer system.
11.1.2

HELLO Command

Equipped with the codes to obtain access to the system, the user
should find a terminal and turn the LINE-OFF-LOCAL knob to LINE.

This

puts the terminal on-line to RSTS-ll, that is, opens a line of
communication between the computer and the terminal.
Once the terminal is on-line, type the word:
HELLO
followed by the RETURN key.
join the system.

This tells RSTS-ll that a user wishes to

RSTS-ll will print a number sign (#) at the left

margin of the paper and wait for the user to type his projectprogrammer number and the RETURN key.
11-1

The system responds by printing:

PASSWORD:
and waiting for the user to type his password followed by the RETURN
key.

These characters are not printed at the console.

If the codes

are acceptable to the system, the message:
RSTS V~lA -JOB ~l TTY~ 12-MAY-71 12:3~ PM
MESSAGES OF THE DAY ARE:
is printed.

If the codes are incorrect, the error message "INVALID

ENTRY - TRY AGAIN" is printed and the user can try again.
The entire process of entering the system would look as follows
(although the RETURN key is typed to enter a line to the system it
does not echo on the terminal paper except to perform a carriage
return/line feed operation) :
HELLO

# l~~,l~l
PASSWORD:
RSTS V~lA -JOB ~l TTY~ 12-MAY-71
MESSAGES OF THE DAY ARE:
NEW OR OLD--

12:3~

Once successfully logged onto the system, the user can type "NEW" to
create a new program, "OLD" to retrieve a program previously saved, or
any other command in this chapter.
11.1.3

BYE Command

Whenever the user is ready to leave the terminal, he types the
command:
BYE
followed by the RETURN key.

This tells RSTS-ll that the user has re-

quested to be dismissed from the system.

RSTS-ll then removes from

core and disk any temporary files which had been created by the system
for the user.

Any files created by the user and still remaining open

on disk (or any I/O device) are closed and saved for the next session.
Before leaving the terminal, the user should turn the LINE-OFFLOCAL knob to OFF.

(Turning the knob to LOCAL means that the terminal

has power, but is not connected to the system.
a typewriter.)
11-2

It then operates as

11.2

CREATING A USER PROGRAM
In order to create a new user program, at any time a user can

issue the NEW command as follows:
NEW
followed by the RETURN key).

The system responds by printing:

NEW PROGRAM NAME-to which the user responds by typing the name of the new program.
When typing a new BASIC program, the file name extension .BAS (for
BASIC) is added to the name by the system.
Alternatively, the user can give the command NEW followed by the
program n~ue, to avoid having the system prompt the typing of the
program name:
NEW FOO
is equivalent to
NEW
NEW FILE NAME--FOO
When the NEW command is given, it:
a.

Deletes any program currently in core, and

Causes RSTS to remember the new program name.
NEW

DTA~:FOO

is meaningless.

All checking for duplicate files occurs when the SAVE

command is given.
Following the creation of a new file with an acceptable file
name, the user can begin to type his program, beginning each line with
a line nwnber.
The user has the option of typing the RETURN key instead of
indicating a file name.

This will cause BASIC to create a file called

NONAME which can be referenced later as NONAME.

At any time, this

name can be changed (see sections 7.7 and 11.5.5).

Only one file

with the name NONAME can exist at anyone time for a given
user.

The creation of the file NONAME is shown below (the

11-3

RETURN key, although typed, does not echo) :
NEW
NEW PROGRAM NAME-READY
If the SAVE command is now given, it will create NONAME.BAS as
a file.
11.3

RECALLING AN OLD PROGRAM
When the user desires to recall the source file of an old BASIC

program (previously saved on a storage device), he gives the OLD
command as follows:
OLD
to which the system replies:
OLD PROGRAM NAME-The user then types the name of the old BASIC file containing the
program.

Alternatively, the user can indicate the old file name

without prompting, as follows:
OLD TAXES
which calls the old file TAXES from the disk.

If the file is not

available on the disk or if it is protected against that user, an
appropriate message is printed.
If a file name is preceded by the $ character, the file with
the given name is taken from the system library.

For example:

OLD $OOG
calls the file DOG from the system library.

The system manager or

group instructor will generally provide users with a list of files in
the system library which are available for their access.
these files are protected against change by users.)

11-4

(Many of

Where no file name is indicated, BASIC looks for the file NONAME
(which could have been created by the user or the system, see section
11.2).

For example:
OLD
OLD PROGRAM NAME-READY

Whatever had been stored in the file named NONAME is now in core and
available to the user.
The OLD command can only retrieve BASIC source programs.
programs can be run but not changed.

compiled

Any program called with the OLD

command can be edited by the user at the terminal.
11.4

EDITING OF USER PROGRAMS
During the course of typing a program at the terminal or after a

program is seen to be incorrect, changes can be made in the text of a
program.

These changes are made in what is called the editing phase

of BASIC, between the time when the system prints READY and the time
when the user types RUN.

(During this time, system commands and

Immediate Mode statements can be executed.)
The simplest type of correction is done during the typing of a
line before the line is entered to the system with the RETURN key.
For example:
l~

DEF FUN(X)=

If the user realizes he has typed FUN instead of FNU, he can type
the RUBOUT key once for each character to be erased.

The RUBOUT key

causes the erased character to be echoed on the user terminal
between back slashes as they are erased.

For example:

ABC<RUBOUT><RUBOUT>DEF
Typing the above is printed on the terminal as follows:
ABC\CB\DEF

11-5

If the RETURN key is typed at the end of the above line, the system
would receive it as follows:
ADEF
The letters Band C have been erased.
If the user decides that his easiest course is to delete the
entire line, and he has not yet typed the RETURN key, then he can
type CTRL/U (hold down CTRL and U keys), which performs this function.
If the RETURN key has been typed, then the line may merely be retyped;
the second version will replace the first in the computer memory.
11.4.1

DELETE Command

The DELETE command is used to remove one or more lines from the
user program currently in core.
DELETE

For example:

l~~

causes line number 100 to be deleted.

(The user should first be cer-

tain that no other line references line number 100 unless that line
is to be replaced.)
DELETE

1~~-2~~

causes all the program lines between and including line numbers 100
and 200 to be deleted.

If 100 and/or 200 do not exist in the program,

any lines within the range from 100 to 200 are deleted.
If several groups of lines are to be deleted, then the user can
type:

which deletes all lines between 100 and 200, 300 and 400, and 1000
and 1100.
If only one line is to be deleted, it may be more convenient
merely to type the line number and the RETURN key
l~

11-6

which is equivalent to:
DELETE 1.0
11.4.2

LIST Command

The LIST command is used to obtain a clean printed copy of all or
part of the user's current program.

This is especially useful during

and after an editing session in which the original program is changed.
In order to obtain a printed copy of the entire program as it
currently exists within the system, type:
LIST
In order to list a single line, type:
LIST 1.0.0
to type line 100.
In order to list a section of the program, type:
LIST lfl.0-2.0.0
which will cause the listing of the entire program from line number
100 to line number 200 inclusive.
In each of the above cases, BASIC prints a program header containing the program title, date, and time.

If this header material is not

desired (as it might not be for normal editing), the command may be
given as LISTNH to delete the header material.

To summarize:

Meaning

LIST Command
LIBT

List the entire user program as it currently exists.

LISTNH

Same as LIST, but without a program header.
List line n.

LIST n
LISTNH

Y'\

List line n without a program header.

LIST nl-n2

List lines nl through n2

LISTNH nl-n2

List lines nl through n2, inclusive, without a
program header.

11-7

A ? is printed at the left of each line which BASIC-Plus considers
to be in error.
?l~

11.4.3

For example:

PPRINT A+B

CaNT Command

As explained in section 4.2 on Program Debugging, the STOP statement can be used to cause halts at various points in a user program.
Immediate Mode examination of values or changes can be made to the
program, followed by the resumption of program execution.

Once a

program has been stopped, it can be restarted at the point at which
execution stopped by giving the
CaNT
command followed by typing the RETURN key.

When the CONT command is

given,execution continues with the next executable statement following
the STOP.
11.5

MANIPULATING USER PROGRAMS
The commands in this section enable the user to compile, save,

run, and rename his files.

These are all operations performed on a

program as a whole (either in core or as a file)

and are used once

a complete program has been prepared at the terminal.
11.5.1

RUN Command

The RUN command is used to cause the execution of any BASIC
program, either source or compiled.

(Source programs are stored as

the user typed them; compiled programs are files described in
section 11.5.7.)
In order to run the program currently in core, the user simply
types:
R~

This causes the execution of the program in core.

A program header

is printed after the RUN command is given, consisting of the program
name, date, and time.

If this information is not desired, the

command
R~NH

11-8

should be given.
RUNNH executes the current program without printing
the header material.
Where it is desired to run a program not in core, the command:
RUN FILENAME
can be given.

This command causes BASIC to search for the fiie

FILENAME on the disk, load, compile it (if necessary), and run it if
it is found.
If FILENAME.BAS (source) and FILENAME.BAC (compiled) both exist,
BASIC will execute FILENAME.BAC since it requires less time.
;tufc~~.J FILeu~",c:;. i!lA.c..

In order

to retrieve and execute FILENAME.BAS~ it is necessary to issue
separate OLD and RUN commands.
editing to be performed.

The file is then available for any

Where the file to be run is not present on the disk

but on

another storage device, the format:
RUN DEV:FILENAME
where DEV: is the designation of the storage device.

For example:

RUN PTR:
reads a BASIC program from the high speed reader and runS it.
As with the OLD command, the character $ appearing before the
name of a file indicates that the file resides in the system library.
If the file can be accessed by the user, he will be allowed to run
it (see section on file protection, 7.7).

Only files

wit~

the

extensions .BAS and .BAC can be RUN.
11.5.2

SAVE Command

The SAVE command is used to store BASIC source programs on the
disk as follows:
SAVE
The program currently in core is saved under its file name with the
extension .BAS.

If a file of the same name exists, then SAVE returns

the error message:
FILE EXISTS - USE 'REPLACE'
11-9

Where the current name of the file is not the

desire~

name, the

format:
SAVE FILENAME
can be used, which saves the program currently in core under the
name FILENAME.BAS.
In cases where the desired storage device is not the disk, the
format:
SAVE DEV:FILENAME
is used where DEV: indicates the device designation.
stored as FILENAME.BAS.

The file is

For example:

SAVE DTA4: ROPE
saves the file ROPE.BAS on DECtape 4.
The SAVE command is used only with source files and cannot be
used with compiled files.

When a program is saved,

under some name,

the program is still in core to be used or ignored as the user wishes.
To obtain a listing of his program on the line printer, the user
can type:

To punch a tape of his program, the user can type:

11.5.3

UNSAVE Command

The UNSAVE command is used to remove a file from a storage
device.

The form:
UNSAVE FILENAME.BAC

removes the file FILENAME.BAC from the disk.
device assumed is the disk.

(Unless specified, the

If the command is given:

UNSAVE FILENAME
11-10

. BASIC attempts to remove first the file FILENAME.BAS and then the
file FILENAME.BAC.

Unless only one of the two is specified in the

command, both are removed if they are found.
To indicate another device, the form:
UNSAVE DEV:FILENAME
is used, where DEV: is the device designation, for example:
UNSAVE DTA4: Faa
removes the file(s) FOO.BAS and FOO.BAC from DECtape 4 if they are
found.
11.5.4

CHAIN command, Program Overlaying

If a user program is too large to be loaded into core and run in
one operation, the user can segment the program into two or more
overlays.

Each overLay section is assigned a name and control can

be transferred from one section to another with the CHAIN command.
The CHAIN command is of the form:

.
5<line number>j!
CHAIN <s tr-I--ng> ,
in which the string is the name of the next overlay section and the
line number specifies the line number at which to begin execution.
If no line number is specified, execution begins with the lowest
numbered line. For example:
CHAIN "PHASE2"

causes the current program segment to be overlayed with segment
"PHASE2".

Execution begins with line

in the new segment.

Communication between various program segments can be done by
means of the user's file area.
When the CHAIN command is executed, all the user's open files
. are closed, the new segment is loaded, and execution continues.
~~~*;;;{?
~'.\
, 1$

'
t \'
5j i.""

CI ( "{At
)'

,t.

11-11

11.5.5

RENAME Command

The RENAME command causes the name of the program currently in
core to be changed to the specified name.

For example:

RENAME NEWNAM
The old name of the program in core is discarded and it is now known
as NEWNAM

If the SAVE command is given:
SAVE

the file NEWNAM. BAS
1l.5.6

would be stored on the disk.

REPLACE Command

The REPLACE command is used when the program in core has the
same name as a file on the disk and the user wishes the program in
core to become the new file with that name.

The command is simply

of the form:
REPLACE FILENAME
REPLACE is like SAVE, but destroys without notice the old copy of
same file, if i t exists.
11.5.7

COMPILE Command

Normally RSTS-ll reads each line of a user's program as it is
typed and, if acceptable, translates the line into a form
easily understood by the PDP-ll computer.

As lines within the

program are altered, only those lines which are changed need to be
recompiled (i.e., translated).

When the SAVE command is given, only

the source version of the program (i.e., the text that is typed in
response to the LIST command) is retained in the specified place.
In response to the OLD command, BASIC reads the text from a file
and compiles it in much the same manner as is done when the program is
read from the user's keyboard.
Once a program is completely developed and debugged, it may be
desirable to avoid the time-consuming practice of compiling the
program every time it is fetched from the library.
the COMPILE command has been provided.

For this reason,

This command permits the

user to save an image of his compiled program, rather than (or in

11-12

addition to} the source text of the program.

This compiled program

may be called in from the disk and executed with a minimum of overhead
by use of the RUN command (see section 11.5.l).
Due to the transformation that takes place when a program is
compiled, a file with the extension .BAC can only be executed, it
cannot be edited.

Therefore, the user can issue the RUN command

with respect to these compiled files, but the file cannot be brought
into core with the OLD command.

If the current file name (i.e., that which is typed in the heading of a listing) is "FILE,01", then the command
COMPILE
will save the compiled program in a file named FILE,0l.BAC.

another name is desired for the compiled file, it may be specified.
COMPILE Faa
will generate a file named FOO.BAC.
11.6

SYSTEM STATUS REPORTS

11.6.1

LENGTH Command

The LENGTH command returns the length of the user's current
core program.

For example:

LENGTH
2K OF CORE USED
102,4

At least 2K of core (IK = ~ words) is reserved for each user wi th
a maximum of 12K per user.

The maximum size of a user program

depends upon how much core is physically on the system and how much
core the system administrator permits any single user to "own".
11.6.2

CATALOG Command

Giving the C;:ALOG command causes the user's file directory to
be printed 2 ,,, :::
2 (where no device is specified the

t=II"

l.. .

list of user files isAprinted on the terminal).

.. tI.c.

~ t
11-13

For example:

CATALOG
Faa

name

.BAS

extension

size

protection

4-APR-71

29-MAR-71

creation date
access date

10:50 AM

t
I

time

To obtain a CATALOG of files on a device other than the disk,
one can give the command
CATALOG DEV:
For examplc::
CATALOG $
lists the files in the system library;
CATALOG

[l~~,l~lJ

lists the files owned by user account 100,101; and
CATALOG DTf.4:
lists the files on DECtape unit 4.
11.7.

USING INPUT/OUTPUT DEVICES

11.7.1

TAPE Command

The TAPE command is used to disable the terminal echo feature
when reading a paper tape with the low-speed (terminal) reader.

The

command is given as follows:
TAPE
followed by the RETURN key.

The tape is then inserted in the low-

speed reader and the reader control switch set to START.
Prior to giving the TAPE command, the user will have set up
conditions such that the system expects the program.

For example,

giving the following commands:
NEW Faa
TAPE
causes the system to await the new program file Faa which is to be
11-14

entered to the system via the terminal tape reader.

Giving the TAPE

command disables the echo feature so that the program is not listed
on the terminal as it is read.

The same function would be served by

the following commands:
OLD FOO
TAPE
11.6.2

KEY Command

Since nothing input at the terminal is echoed once the TAPE
command is given, the KEY command is used to enable the user to see
what he is typing again.

The command is typed as:

KEY
although it will not be printed on the terminal

~aper.

Once the

RETURN key is typed, all other characters typed at the keyboard are
echo printed.

It may sometimes be necessary to type tc to have

RSTS-ll "hear" the KEY command.
11.7.3

ASSIGN Command

The ASSIGN command is used to reserve an I/O device for the use
uf a single programmer.

The command is given in the form:

ASSIGN DEV:
where DEV: is the device designator (see Table 11.1).

If the device

is present on the system and available for use, the system returns
the message:
READY
If the device is not available for use, the message:
DEVICE NOT AVAILABLE NOW
is returned.

For example:

A8S IGN LPT:
~
READY
ASSIGN PTP:
DEVICE NOT AVAILABLE NOW

11-15

TABLE 11.1
DEVICE DESIGNATORS
Device

Code
P1R:
pip:

high-speed paper tape reader
high-speed paper tape punch

CPR:

card reader

MSR:

mark sense card reader

Lpf:

line printer

DTXYI: to

DECtape units

DTJ/.7 :

-BBff:

~g",~:

11.7.4

YI to 7

disk
Teletype n in the system

DEASSIGN Command

The DEASSIGN command is used to release the specified device to
the device pool within the system (for use by other users).

If no

device is specified, all assigned devices are released from that
project-programmer number.

For example:

DEASSIGN LPT:
releases the line printer.
DEASSIGN
releases all devices previously assigned by that user.

If a

DEASSIGN command is not given before the user leaves the system, an
automatic DEASSIGN is performed when the user gives the BYE command.
11.8

SPECIAL CONTROL CHARACTERS

11.8.1

RETURN Key

Typing the RETURN key echoes as a carriage return/line feed
operation on the terminal, as long as the terminal is not in TAPE
mode.

11-16

11.8.2

ESCAPE or ALT MODE Key

The ESCAPE key also terminates the current typed line and causes
it to be entered to the system.

However, the ESCAPE key echoes on

the terminal paper as a $ character and does not perform a carriage
return/line feed.
11.8.3

LINE FEED Key

The LINE FEED key is used to continue the current logical line
of input on an additional physical line.

The LINE FEED key does not

echo on the terminal paper but does perform a carriage return/line
feed operation when used with the BASIC-Plus system.
Line feeds will produce errors in the user's programs if included
in constants (including string constants), verbs, or user specified
names for variables or functions.
11.8.4

RUBOUT Key

The RUBOUT key is used as an eraser for the current line.

typed in TAPE mode, the RUBOUT key is ignored; otherwise, it causes
the character most recently typed to be deleted.

The erased char-

acters are shown on the terminal paper between back slashes.

For

example:
l~

LEF X=X*X

could be corrected by typing the RUBOUT key 7 times

(to remove the

F) and typing the remainder of the line correctly.

The line would look

as follows on the terminal paper:
l~

LEF X=X*X,X*X=X F~ X=X*X

and would appear to the system as:
l~

LET X=X*X

In cases where the mistake is toward the beginning of a line, it may
be easier to simply retype the entire line.
l~
l~

LEF X=X*X
LET X=X*X

11-17

For example:

Once the second line is entered to the system, the first line numbered
10 is deleted.
11. 8. 5

CT RL/ C

By typing a CTRL/C (hold down the CTRL key and type the C key,
release both), the user causes BASIC to return to command mode, where
commands can be given or editing done.

CTRL/C stops whatever BASIC

was doing at the time and returns control of the system to the user.
11.8.6

CTRL/U

The CTRL/U combination deletes the current input line.

This is

useful when a long command has been typed and is no longer wanted.
Rather than use the RUBOUT key repeatedly, CTRL/U cancels the entire
line.

This feature can be used when typing either commands or state-

ments.

The entire physical line is deleted.

11.8.7

CTRL/O

The CTRL/O combination suppresses output on the Teletype until
the next time CTRL/O is typed (or CTRL/C is typed).

When a program

produces a large amount of output (usually in tabular form), the user
may not wish to wait for the printing of the complete information.
CTRL/O enables the user to monitor the output while not stopping i t
completely.

Typing CTRL/O while output is occurring still allows

the computer to output the data, but the Teletype does not print it.
This speeds up the output process, since the Teletype is a rather
slow device.

The second time CTRL/O is typed, the output is again

sent to the Teletype for as long as the user wishes.
CTRL/C, on the other hand, will completely stop the output.
Think of CTRL/O as a switch, the first setting of which creates a
condition and the second setting releases the condition.
11.8.8

TAB Character

The TAB character or CTRL/I combination allows the user to
insert a tabular format into his typed material.

When entering a

program to the system, the TAB character allows formatting such as is
shown in section

9.5.

The BASIC editor considers each line as

being broken into tab stops eight spaces apart across the line.
Typing the TAB character causes the printing head to move to the
next of those stops on the line.

If using a model 33 Teletype, the TAB echoes as spaces.

The

model 35 Teletype has built-in hardware tabs.
11.8.9

CTRL/P

The CTRL/P combination is used as a switch to engage or disengage the

software tabs created with a model 33 Teletype.

If the

printer does not position itself at the next tab stop in response to
a TAB, then CTRL/P should be typed to "toggle" this switch.
11.8.10

CTRL/B

The CTRL/B combination is used as a switch to stop and start
echoing at the user terminal.

This feature is useful when operating

remotely from a half-duplex Teletype.
RSTS-ll assumes that the terminal user is at a full duplex
Teletype, which requires that characters typed at the user terminal
be echoed by the system at the user's printer.

Some Teletypes provide

this local echo function as a part of their normal functioning.

Such

Teletypes are easily recognized, since each character typed by the
user is echoed twice:

once by the Teletype and once by the RSTS system.

When this symptom is seen, typing CTRL/B will cause RSTS to suppress
its Teletype character echo, so that only the local echo is printed.
Conversely, RSTS may think a Teletype is half duplex when actually
it is full duplex; in this case, typed characters are not echoed at
all.

Typing CTRL/B will then alter the assumption RSTS makes, and

resume Teletype echoing.
11.8.11

CTRL/Z

The CTRL/Z combination is used to mark the end of a file; when
inputting data from a file, a CTRL/Z character marks the end of the
recorded data.

The message "END OF FILE ON DEVICE" is given when a

tz is detected.

11-19

APPENDIX A
BASIC-PLUS LANGUAGE SUMMARY
A.l

Summary of Variable Types
Examples

variable Name
Floating Point

single letter
optionally followed by a
single digit

A
I

Integer

any floating point variable
name followed by a % character

B%
D7%

Character String

any floating point variable
name followed by a $ character

M$
Rl$

Floating Point
Matrix

any floating point variable
name followed by one or two
dimension elements in
parentheses

S (4)
E(5,1)
N2 (8) V8(3,3)

Integer Matrix

any integer variable name
followed by one or two dimension elements in parentheses

A%(2)
I%(3,5)
E3 %(4) R2 %(2,1)

Character String
Matrix

any character string variable
name followed by one or two
dimension elements in parentheses

C$(l)
S$(8,5)
A2 $ ( 8) VI $ ( 4 , 2)

A.2

SUMMARY OF OPERATORS
Operator

Ari t-hmetic

Operates Upon

exponentiation
unary minus
multiplication, division
addition, subtraction

numeric variables
and constants

<
<=
>
>=
<>

equals
less than
less than or equal to
greater than
greater than or equal to
not equal to
approximately equal to

string or
numeric variables
and constants

Logical

NOT
AND
OR
XOR
IMP
EQV

logical negation
logical plroduct
logical sum
logical exclusive or
logical implication
logical equivalence

relational expressions composed
of string or
numeric elements
with relational
operators

String

concatenation

string constants
and variables

Matrix

+,-

dimensioned variaddition and subtraction
See
of matrices of equal dimen- ables.
Section 8.5.1
sions, one operator per
for further destatement
tails.
multiplication of conformable matrices
scalar multiplication of
a matrix, see Section 8.5.1

*,/
+,Relational

*
*

A-I

A.3

SUMMARY OF FUNCTIONS
~

Function

Mathematical

ABS(X)
ATN (X)
COS (X)
EXP (X)
FIX (X)
INT (X)
LOG (X)
LOG1.0'(X)
PI
RND (X)
SGN(X)
SIN (X)
SQR (X)
TAN (X)

pas (X)

TAB (X)

String

CHR$(X)

System

DATE $ (.0')

Explanation
returns the absolute value of X
returns the arctangent of X in radians
returns the cosine of X in radians
returns the value of e X, where e=2.l41S
returns the truncated value of X,
SGN(X)*INT(ABS(X»
returns the greatest integer in X which
is less than or equal to X
returns the natural logarithm of X, log X
returns the common logarithm of X, 10gl~X
has a constant value of 3.1415926
returns a random number between
and 1
returns the sign function of X, a value
of 1 preceded by the sign of X
returns the sine of X in radians
returns the square root of X
returns the tangent of X in radians

returns the current position of the print
head for the device X, .0' is the user's
Teletype.
(This value is imaginary for
disk files.)
moves print head to position X in the
current print record, regardless of
current position.

returns a character string having the
ASCII value of X. Only one character
is generated.
ASCII (A$)
returns the ASCII value of the first
character in the string A$.
LEFT(A$,N)
returns a substring of the string A$
from the first character to the Nth
character (the leftmost N characters) .
RIGHT(A$,N) returns a substring of the string A$
from the Nth to the last character (the
rightmost characters of the string
starting with the Nth character).
)
t U~ (ti t -> A.$ , t~ ) MI D (A $ , N1 , N2 returns
a substring of the string A$
starting with character Nl and being N2
\ip..L (A~)
characters long (the characters between
and including the Nl to Nl+N~~haracters) .
tJ ut1$ (~)
LEN (A$)
returns the number of chara'cters in the
string A$, including trailing blanks.
St'~:t. (tJ)

DATE$(N)

TIME$ (.0')

returns the current date in the following format:
2-MAR-71
returns a character string corresponding
to the Julian date N+70,OOO
DATE $ (1) = ".0'I-JAN-7.0'''
DATE $ (24,0) = ",05-MAY-7.0'''
returns the current time of day as a
character string as follows:
TIME$(O) = ".0'5:3.0' PM"

A-2

Summary of Functions (Cont.)
Function
TIME$ (N)

TIME(~)

TIME (1)
TIME (2)
SLEEP (X)
WAIT (X)

WAIT(~)

Matrix

TRN (X)

INV (X)
DET

A.4

Explanation
returns a string corresponding to the
time at N minutes before midnight, for
example:
TIME$(l) = "11:59 PM"
TIME$(l*) = "12:0'0' AM"
TIME$(721)= "11:59 AM"
returns the clock time in seconds since
midnight, as a floating point number.
returns the central processor time used
by the current job in seconds.
returns the connect time (during which
the user is logged into the system) for
the current job in seconds.
dismiss this job for X seconds
causes the currently running program to
be dismissed for either X seconds or until a line is typed at the user terminal,
whichever comes first.
Generates error
condition #15 if wait is exhausted.
causes the system to wait for input
from the user terminal with no time
limit.
returns the transpose of the matrix X,
see section 8.5.2.
returns the inverse of the matrix X,
see section 8.5.2.
following an INV(X) function evaluation,
the variable DET is equivalent to the
determinant of X.

SUMMARY OF BASIC-PLUS STATEMENTS
The following summary of statements available in the BASIC-Plus

language defines the general format for the statement as a line in
a BASIC program.

If more detailed information is needed, the reader

is referred to the section(s) in the manual dealing with that particular statement.
In these definitions, elements in angle brackets are necessary
elements of the statement.

Elements in square brackets are necessary

elements of which the statement may contain one.

Elements in braces

are optional elements of the statement.
The various elements and their abbreviations are described
below:

variabZe
Zine number

var

Any legal BASIC variable as described
in A.l or section 2.5.2
Any legal BASIC line number described
in section 2.2
A-3

expression

exp

message

Any legal BASIC expression as described
in section 2.5
Any combination of characters

aondition

aond

Any logical condition as described in
section 3.5

argument(s) or arg

Dummy variable names

statement

Any legal BASIC-Plus statement

string

Any legal string constant or variable

proteation

Any legal protection code as described
in section 7.7

valuers)

Any floating point integer or character
string constant

list

The legal list for that particular
statement

dimension(s)

One or two dimensions of a matrix, the
maximum dimension(s) for that particular
statement.
Manual
Section

Statement Formats and Examples
RBM

3.1

line number REM <message>
line number <statement> !<message>
REM THIS IS A COMMENT
l~
15 PRINT
!PERFORM A CR/LF
LET

3.2

<exp>
line number fLETJ<var>
55 LET A=4~: B=22
B,C,A=4.2
!MULTIPLE ASSIGNMENT
6~
DIM

3.6.2

line number
l~

line number
75

DIM <var(dimension(s)>
DIM A (2~) , B$ (5 , l~) , C%(45)
DIM #<exp>, <var(dimension(s)>=<exp>
DIM #4, A$(1~~)=32,B(5~,5~)

RANDOMIZE
line number
55

RANDOMIZE
RANDOMIZE

IF-THEN, IF-GOTO
line number

IF <aond>

55
6~

95
IF-THEN-ELSE

line number
3~
5~

7 .. 5

3.6.3

ITHEN<statement>
:THEN<line number> I
GOTO<Zine numbe:>J
IF A>B OR g-5C THEN PRINT "NO"
IF FNA(R)= B THEN 25~
IF L<xt2 AND L<>~ GOTO 345

3.5

-THEN<statement> ~
IF <aond> :THEN<Zine number>
GOTO<Zine number>

9.5

.J ELSE<statement> 7( ELSE< Zine number> j

IF B=A THEN PRINT "EQUAL" ELSE PRINT "NOT EQUAL"
IF A>N THEN 2~~ ELSE PRINT A
IF B= R THEN STOP ELSE 8~
A-4

FOR

line number
2~

FOR<var>=<exp>TO<exp>[STEP<exp>}
FOR 1=2 TO 4~ STEP 2
FOR N=A TO A+R

3.6.1

FOR-WHILE, FOR-UNTIL
9.6
line number FOR <var> = <exp> [STEP<exp >1 WHILE <cond>
UNTIL
84 FOR I = 1 STEP 3 WHILE I<X
74 FOR N = 2 STEP 4 UNTIL N>A OR N=B
05 FOR B= 1 UNTIL B>l.0

3.6.1

line number
25
6.0

NEXT <var>
NEXT I
NEXT N
3.9.3
5.5.1
6.4

DEF, single line
DEF FN <var (arg»=<exp (arg»
DEF FNA(X) = xt2 + X

line number
2.0

9.1

DEF, multiple line

line number DEF FN<var> (arg)
<statements>
number FN <var>= <exp>
v
line number FNEND
!FACTORIAL FUNCTION
1.0 DEF FNF (M)
2.0 IF M=l THEN FNF=l ELSE FNF=M*FNF(M-1)
3.0 FNEND
1~·.~ ~

v,t-~

3.4

GOTO

line number

1flfl

GOTO <line number>
GO TO 5.0

ON-GOTO

line number
75

ON <exp> GOTO <list of line numbers>
ON X GO TO 95, 15.0, 45, 2.0fl

line number

GOSUB <line number>
GOSUB 2fl.0

9.2

GOSUB

9fl

3.8.1

ON-GOSUB

line number
85

ON <exp> GOSUB <list of line numbers>
ON FNA(M) GOSUB 2fl.0, 25.0, 4.0fl, 375

9.3

RETURN
RETURN

3.8.2

RETURT\J

line number
375
CHANGE

Zine numbel'
25

7fl
75

CHANGE r<num~1"ical var>l TO r<strin~ var>

~str~ng var>

CHANGE A$ TO X
CHANGE M TO R$
CHANGE B TO B$

A-5

~numer~cal var~

5.2

OPEN

line number
1~
2~
3~

OPEN <string>[FOR

~~~~J

{

AS FILE <exp>

OPEN "PTP:" FOR OUTPUT AS FILE B1
OPEN "FOO" AS FILE 3
OPEN "DTA4:DATA.TR" FOR INPUT AS FILE 1fiJ

line number
1fiJfiJ
255

7.6
10.6

CLOSE <list of exp>
CLOSE 2
CLOSE 1fiJ, 4, N1

READ <list of variables>
READ A, B$, C%, F1, R2, B (25)

3.3
3.9
10.1

DATA <list of values>
DATA 4.3, "STRING",85,lE+4,49,75.fiJ4

3.3
3.9
10.1

RESTORE
RESTORE

3.3
3.9
10.2

READ

line number
25
DATA

line number
3~fiJ

RESTORE

line number
125
PRINT

line number
25
75
45
PRINT USING

line number
54
55
INPUT

line number
25
55
INPUT LINE

line number
4fiJ
75

7.2
7.5
10.5

(" r

'")

"")

PRINT ~ t#<exp>3j<list>j
PRINT
!GENERATES CR/LF
PRINT "BEGINNING OF OUTPUT";I,A*I
PRINT #4, "OUTPUT TO DEVICE" FNM(A)t2;B;A

3.3
3.11
5.4
6.3
7.3
10.4

9.8.1
PRINT £#<exp>,}USING <string>,<list>
10.4
PRINT USING "##.##",A
PRINT #3, USING"\'###.## ,,'\.##tttt" , "A=" ,A, "B=" ,B

INPUT #<exp>,J < lis t>
INPUT "TYPE YOUR NAME "
INPUT # 8, A, N, B$

INPUT LINE ~<exp>,J<string>
INPUT LINE R$
INPUT LINE #1, E$

NAME-AS

5.3
3.10
7.4
10.3
9.9
10.3

7.7

line number
455
27fiJ

NAME <string> AS <string>l<proteation>}
NAME "NONAME" AS "FILE1"
NAME "DTA4:MATRIX" AS "MATA1"<48>

KILL

7.8

line number
45

KILL <string>
KILL NONAME

A-6

ON ERROR GOTO

9.4

line number
1.0
525
526
RESUME
line number
1.0.0.0
655

ON ERROR GOTO <line number>
ON ERROR GOTO 5.0.0
ON ERROR GOTO !DISABLES ERROR ROUTINE
ON ERROR GOTO.0
!DISABLES ERROR ROUTINE
9.4
RESUME <line number>
RESUME
!OR RESUME .0 ARE EQUIVALENT
RESUME 2.0.0
3.12

STOP

line number
75

STOP
STOP

line number
545

END
END

3.12

END

Matrix Statements
MAT READ
line number
55
9.0
MAT PRINT
line number
1.0
9.0
95
97
MAT INPUT
line number
1.0
2.0
3.0

8.1
MAT READ <list of matrices)
DIM A(2.0), B$ (32), C% (15,10)
MAT READ A, B$(25), C%
8.2
MAT RRINT [#<exp>,
<matrix name>
DIM A(2)l), B (15,2.0)
MAT PRINT Ai
!PRINT 10*10 MATRIX, PACKED
MAT PRINT B (1.0 ,5)
!PRINT 10*5 MATRIX, FIVE
!ELEMENTS PER LINE
MAT PRINT #2, Ai
!PRINT ON OUTPUT DEVICE 2

MAT INPUT [#<exp>.J 3 <list of matrices>
DIM B$(4.0), F1%(35)
OPEN "DTA3:FOO" FOR INPUT AS FILE 3
MAT INPUT #3, B4, F1%

~E~l

MAT initialization
line number MAT <matrix name>
1.0
15
2.0
95

CHAIN

~g~ f dimension{s} 1

8.3

8.4

DIM B (15,1.0), A(l.0) , C% (5)
MAT C% = CON
!ALL ELEMENTS OF C%(I)=l
MAT B
IDN(l.0,1)l)
!IDENTITY MATRIX 1.0*1.0
MAT A = ZER
!CLEARS MATRIX ELEMENTS TO

I.,. .

< ;I,•.:,)

A-7

f ~ (;- .... ) 3

Statement Modifiers
IF

9.7.1
<statement>
l~

IF <condition>
PRINT X IF X<>~

UNLESS

9.7.2

UNLESS<condition>
PRINT A UNLESS A=~

FOR

9.7.3
<statement>
75
8~

FOR <var> = <exp> TO <exp>tSTEP<exp>}
LET B$(I) = "PDP-II" FOR I = 1 TO 25
READ A(I) FOR 1=2 TO 8 STEP 2

WHILE

9.7.4
<statement>
l~

WHILE <condition>
LET A(I) = FNX(I) WHILE 1<45.5

UNTIL

9.7.5

<statement>
115

UNTIL <condition>
IF B>~ THEN A(I)=B UNTIL 1>5

A-8

APPENDIX B
BASIC-Plus Command Summary

Command

Explanation

Section

HELLO

Indicates to RSTS that a user wishes to log
onto the system. Allows the user to input
project-programmer number and password.

11.1.2

BYE

Indicates to RSTS that a user wishes to leave
the terminal. Closes and saves any files remaining open for that user.

11.1.3

NEW

Clears the user's area in core and allows the
user to input a new program from the terminal.
A program name can be indicated following the
word NEW or when the system requests it.

11.2

OLD

Clears the user's area in core and allows the
user to recall a saved program from a storage
device. The user can indicate a program name
following the word OLD or when the system requests it. If no device name is given, the
file is assumed to be on the system disk.

11.3

DELETE

Allows the user to remove one or more lines
11.4.1
from the program currently in core. Following
the word DELETE the user types the line number
of the single line to be deleted or two line
numbers separated by a comma indicating the
first and last line of the section of code to
be removed. !he. w(X~ OE"L~ ~ tr-nli- J.,lttfJ ~I~ ~l'T(M.t p~M.

LIST

Allows the user to obtain a printed listing at
the user terminal of the program currently in
core, or one or more lines of that program.
The word LIST by itself will cause the listing
of the entire user program. LIST followed by
one line number will list that line; and LIST
followed by two line numbers separated by a
comma will list the lines between and including
the lines indicated.

11.4.2

LISTNH

Same as LIST, but does not print header containing the program name and current date.

11.4.2

CONT

Allows the user to continue execution of the
program currently in core following the execution of a STOP statement.

11.4.3

RUN

Allows the user to begin execution of the program currently in core. The word RUN can be
followed by a file name in which case the file
is loaded from the system disk, compiled, and
run; alternatively, the device and file name can
be indicated if the file is not on the system
disk. A device specification without a file name
will cause a program to be read from an input only
device (such as high-speed reader, card reader).

11.5.1

B-1

Command

Explanation

Section

RUNNH

Same as RUN, but does not print header containing the program name and current date.

11.5.1

SAVE

Causes the program currently in core to be
saved on the system disk under its current
file name with the extension .BAS. Where
the word SAVE is followed by a file name
or a device and a file name, the program in
core is saved under the name given and on
the device specified.
A device specification without a file name will cause the program to be output to any output only device
(line printer, high-speed punch).

11.5.2

UN S AVE

The word UNSAVE is followed by the file name
and extension of the file to be removed.
If
no device is specified, the disk is assumed.

11.5.3

CHAIN

Allows the user to combine a segmented program in user core.
Following the word CHAIN
is the name of the next overlay section (assigned with the SAVE command) and, optionally,
a line number on which to begin execution if
the lowest line number is not to be used.

11.5.4

RENAME

Causes the name of the program currently in
core to be changed to the name specified after
the word RENAME.

11.5.5

REPLACE

Same as SAVE, but allows the user to substitute a new program with the same name for an
old program, erasing the old program.

11.5.6

COMPILE

Allows the user to store a compiled version of
his BASIC proqram.
The file is stored on disk
with the current name and the extension .BAC.
Or, a new file name can be indicated and the
extension .BAC will still be appended.

11.5.7

LENGTH

Returns the length of the user's current program in core.

11.6.1

CATALOG

Returns the user's file directory.
Unless
another device is specified following the
word CATALOG, the disk is the assumed device.

11.6.2

TAPE

Used to disable the echo feature on the user
terminal while reading paper tape via
low-speed reader.

11.7.1

KEY

Used to re-enable the echo feature on the
user terminal following the issue of a TAPE
command.

11.7.2

ASSIGN

Used to reserve an I/O device for the use of
the individual issuinq the command. The specified device can then be given commands only
from the terminal whjch issued the ASSIGN.

11.7.3

B-2

Command

Explanation

Section

DEASSIGN

Used to release the specified device for
use by others.
If no particular device is
specified, all devices assigned to that
terminal are released.
An automatic
DEASSIGN is performed when the BYE command
is given.

11.7.4

Special Control Character Summary
RETURN
Key

Enters a typed line to the system, results
in a carriage return/line feed operation at
the user terminal.

11.8.1

ESCape or
ALT MODE
Key

Enters a typed line to the system, echoes
on the user terminal as a $ character and
does not cause a carriage return/line feed.

11.8.2

LINE FEED
Key

Used to continue the current logical line
on an additional physical line.
Performs a
carriage return/line feed operation.

11.8.3

RUBOUT
Key

Deletes the last character typed on that
physical line.
Erased characters are shown
on the terminal between back slashes.

11.8.4

CTRL/C

Causes the system to return to BASIC command
mode to allow for issuing of further commands
or editing.
Echoes on terminal as tC.

11.8.5

CTRL/U

Deletes the current typed line, echoes as
tu and performs a carriage return/line feed.

CTRL/O

Used as a switch to suppress/enable output
of a program on the user terminal.

11.8.7

TAB or
CTRL/I

Performs a tabulation to the next of nine
tab stops (eight spaces apart) which form
the terminal printing line.

11.8.8

CTRL/P

Used as a switch to enable/disable the software tabs created with a Model 33 Teletype
terminal.

11.8.9

CTRL/B

Used as a switch to stop/start the echo
feature at the user's terminal.

11.8.10

CTRL/Z

Used as an end-of-file character.

11.8.11

B-3

"
0
C
.l....L.O.v

APPENDIX C
Error Message Summary

The following messages are printed when an error of the specified
type occurs.

These errors can cause a transfer to a user-written sub-

routine if the ON ERROR-GOTO statement has been used (in which case the
message is not printed).

Many of the following messages are followed

by the phrase AT LINE XXX where XXX indicates the line number at which
the error occurred.

The value of the variable ERR following execution

of the ON ERROR-GaTO transfer is given below.
ERR

Error Message

BAD DIRECTORY FOR DEVICE

File lookup is impossible on the
device specified.

ILLEGAL FILE NAME

The file name given contains embedded blanks or illegal characters.

FILE IS CURRENTLY OPEN

Another user has opened this file.

NO ROOM ON DEVICE

Sufficient storage space on device
specified is not available to store
the file.

Cill~!T

NOT A VALID DEVICE

Device indicated is not present in
the system.

I/O CHANNEL ALREADY OPEN

A file is already open using that
internal file designator.

DEVICE NOT AVAILABLE

Another user has assigned that device for his use.

I/O CHANNEL NOT OPEN

NO file has been opened on the
particular internal file designator
used.

PROTECTION VIOLATION

This file is not available for your
project-programmer code.

END OF FILE ON DEVICE

Program attempted to read beyond
the end of the file.

OPERATION ABORTED

Serious I/O failure.

DATA ERROR ON DEVICE

Parity error detected.

DEVICE OK?

Device is off-line or requires
service.

FIND FILE

Meaning

File is not present on indicated
device.

C-l

ERR

Error Message

Meaning

TELETYPE WAIT EXHAUSTED

User did not respond at the terminal within the allotted time.

FILE OF SAME NAME EXISTS

Attempt to put a second file of
the same name on the same device.

VIRTUAL CORE NOT ON DISK

Attempt to reference virtual core
on a device other than the system
disk.

VIRTUAL CORE EXCEEDED

Not enough disk space left free
to hold the virtual core area required.

VIRTUAL ARRAY NOT OPENED

File containing virtual core
matrix has not been opened before
being referenced.

ILLEGAL I/O CHANNEL

Acceptable I/O internal device
designators are integers from 1
to 12.

LINE TOO LONG

More than 256 byte record read
from an I/O device.

FLOATING POINT ERROR

Underflow or overflow has occurred.

ARGUMENT TOO LARGE IN EXP

Inaccurate results will follow.

ARGUMENT TOO LARGE IN SIN

Inaccurate results will follow.

INTEGER ERROR

Overflow has occurred.

ILLEGAL NUMBER

A non-numeric character was encountered in a number.

TRANSCENDENTAL ERROR

Attempt to take log of
negative number.

IMAGINARY SQUARE ROOT

User requested square root of a
negative number.
(SQR(ABS(X))
returned.

SUBSCRIPT OUT OF RANGE

Undefined element of a matrix
referenced.

OUT OF DATA

User has exhausted DATA statement
pool.

ON-STATEMENT OUT OF RANGE

The expression in an ON-statement
was less than 1 or greater than
the number of line numbers specified.

NOT ENOUGH DATA IN RECORD

User tried to input more data
than present on the next logical
record of the file being used.

ILLEGAL UUO FOR USER

User has executed a SYS function
illegally or with a bad argument.

C-2

or of a

The following messages are given when a fatal error has occurred;
each is followed by the phrase AT LINE XXX where XXX is the line number where the error occurred.

Execution stops after the printing of

one of the following messages.
Error Message

Meaning

MAXIMUM CORE EXCEEDED

User program has overflowed one or
more of the following:
pushdown
list, string storage, I/O buffer
area, or matrix storage.

STATEMENT NOT FOUND

The line specified in a GOTO or
GOSUB statement is not present.

ILLEGAL STATEMENT

An attempt was made to execute a
statement that could not be compiled.

STOP

A STOP statement was the last statement executed, rather than the END
statement.
This message is not
necessarily an error, but provides
the user with the information on
where program execution has stopped.

UNIMPLEMENTED CODE

The BASIC-Plus runtime interpreter
cannot execute the compiled statement.

RETURN WITHOUT GOSUB

A RETURN statement was executed
without a preceding GOSUB statement.

BAD NESTING OF GOSUB OR DEF

A DEF statement was encountered in
the middle of a prior multi-line
function definition.

UNDEFINED FUNCTION CALLED

A reference exists to a user function FN~, which has not been defined.

The following error messages are printed by the BASIC-Plus compiler while a program is being typed or commands are being given and
allow the user to correct mistakes before a program is run.

When the

program is listed, lines containing these errors are preceded by a ?
character.
Error Message

Meaning

ILLEGAL SYMBOL

An improper variable name was used.

ILLEGAL VERB

The word or term following the line
number is not a recognizable BASIC
statement designator.

C-3

Meaning

Error Message
ILLEGAL EXPRESSION

An expression was detected which
does not conform to acceptable expressions in BASIC.
See Section
2.5.

ILLEGAL MODE MIXING

Numbers (floating point or integer)
cannot be combined in an expression
with character strings.

ILLEGAL IF STATEMENT

Either the IF, THEN, or ELSE phrase
is incorrect.
See Sections 3.5
and 9.5.

ILLEGAL CONDITIONAL CLAUSE

The expression following IF in a
conditional expression is not properly constructed.

ILLEGAL FUNCTION NAME

Function name used does not follow
conventions established for userdefined functions.

ILLEGAL DUMMY VARIABLE

One or more dummy variables in a
user-defined function are used
elsewhere in that program.

ILLEGAL FN REDEFINITION

Attempt to redefine a user function.
The first definition is retained
and must be deleted before the
second can be accepted.

ILLEGAL LINE NUMBER(S)

The line number used is out of the
range for line numbers (1 n 32768)
or the number is not an integer.

MODIFIER ERROR

Either the modifier phrase of the
statement is incorrect or BASIC has
interpreted some other error to be
an incorrect attempt at a modifier
phrase.

CAN'T COMPILE STATEMENT

The statement does not make sense
to the BASIC compiler.

EXPRESSION TOO COMPLICATED

Rewrite the expression, using two
or more statements.

ARGUMENTS DON'T MATCH

The number and/or type (numeric or
string) of the arguments with which
a function is called do not agree
with the function definition.

TOO MANY ARGUMENTS

A maximum of eight arguments can
be used with a user-defined function.

INCONSISTENT FUNCTION USAGE

Function is redefined with different number or kind of arguments.
This message is a warning only,
indicating that BASIC is aware of
a change in the function.
C-4

Meaning

Error Message
ILLEGAL DEF NESTING

A DEF statement was detected within
a multiple line function definition.

POR WITHOUT NEXT

No NEXT statement can be found with
a variable corresponding to the
control variable in the FOR statement.

NEXT WITHOUT FOR

No FOR statement can be found with
the control variable corresponding
to the variable in the NEXT statement.

DEF WITHOUT FNEND

A multiple line function definition
was encountered without a FNEND
statement marking the end of the
function.

FNEND WITHOUT DEF

An FNEND statement was found without a preceding DEF statement.

CONSTANT STRING NEEDED

A character string variable is not
acceptable in this uage, a character
string constant must be used.

TOO FEW ARGUMENTS

A device or file name was omitted
in an ASSIGN or RENAME command.

SYNTAX ERROR

Elements within the statement have
been arranged in the wrong sequence.

STRING IS NEEDED

A number was specified where a
character string was expected.

NUMBER IS NEEDED

A character string was specified
where a number was expected.

DATA TYPE E RRO R

The type of term found in the DATA
statement pool did not correspond
to the type of variable about to be
read by the current READ statement.

1 OR 2 DIMENSIONS ONLY

A matrix was specified with more
than two subscripts.

PROGRAM LOST-SORRY

The user attempted to continue his
program execution after receiving
a MAXIMUM CORE EXCEEDED error.

RESUME AND NO ERROR

A RESUME command was given when no
error condition existed. The CONT
(continue) command should be used.

REDIMENSIONED ARRAY

A previously dimensioned matrix is
being dimensioned again.
The
original dimension is maintained.

INCONSISTENT SUBSCRIPT USE

A matrix is being referenced with
a different number of subscripts
than it was defined to have.

C-5

Meaning

Error Message
ON-STATEMENT NEEDS GO TO

ON statement must be followed by a
GOTO and a list of line numbers.

TEXT TRUNCATED

The user typed a program line with
more than 255 characters.

The following errors are fatal and cause a termination of program
execution, but the phrase AT LINE XXX is not printed.
Meaning

Error Message
WHAT?

BASIC-Plus did not understand the
line entered.

NO END STATEMENT IN PROGRAM

When reading a file recalled by an
OLD command, an end-of-file condition was detected before reading an
END statement.

NOT ENOUGH CORE

A previously saved program is too
large to run in core. See the CHAIN
command section.

EXECUTE ONLY FILE

Not possible to LIST or SAVE a compiled program.

STATEMENT NOT FOUND

When chaining to a program, the
starting line specified was not
found.

PLEASE USE THE RUN COMMAND

Attempt to execute a statement in
Immediate Mode which only makes
logical sense in a program.

CAN'T CONTINUE

User changed program or execution
was terminated by a fatal error.

END OF STATEMENT NOT SEEN

A badly formed statement has caused
BASIC-Plus to miss detecting the
end of that statement.

FILE EXISTS - USE 'REPLACE'

An attempt was made to SAVE a file
which was already on the system
disk.
REPLACE will delete the old
file and save the new file.

SWAP ERROR FOR JOB

A disk error occurred while moving
the user's job to or from core. The
user's program is lost.

PLEASE SAY HELLO

The user cannot use the RSTS-II system until he has identified himself.

ILLEGAL IN IMMEDIATE MODE

This statement cannot be executed
in Immediate Mode.

Syd~ tv/I j Woe ~J'1. v~':l co- ~ ~C'utJ·
C.... 6

APPENDIX D
ASCII CHARACTER CODES

Character
S'~
tt

#
$
%
&

(
)

0
1
2
3

4
5
6
7
8
9
<

>
?

ASCII Code No.
(Decimal)

Character

32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63

A
B

C
D
E
F
G
H

I
J
K
L
M

a
p

R
S

T
U
V

w
X
y

Z
[
'\
]

t
+-

ASCII Code No.
(Decimal)
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95

Additional symbols useful on output are as follows:
LF (line feed)
CR (carriage return)

10
13

The above list is not complete; there are 128 characters numbered 0 through 127.

D-l

INDEX
ALT MODE key,
1-5, 11-17
AND,
2-9
Angle brackets, 1-2
Arithmetic operators,
2-4, 2-7
ASCII character codes,
5-5
ASCII function,
5-10
ASSIGN command,
11-15
Asterisk,
9-18, 10-7

.BAC,
7-2, 11-10
Backs1ash,
9-17, 10-7
.BAS,
7-2, 11-10
Braces, 1-4
Brackets, 1-2, 1-3
BYE command, 11-2
CATALOG command,
11-13
CDR: ,
7-1
CHAIN command,
11-11
CHANGE statement,
5-4
Channel, see Internal file designator
Character set,
2-4
Character strings,
5-1
constants,
5-3
variable names,
5-2
Character string
input,
5-7
output,
5-9
CHR$ function,
5-10, 9-19
CLOSE statement,
7-11, 10-14
Colon (:),
2-3, 2-4, 4-2
CON,
8-4
Concatenation operator,
5-10
Condition,
3-8, 9-8, 9-11
Conditional Branch,
3-7
Conditional loop termination,
9-10
Conditional transfer ON-GOTO, 9-3
Constants
character strings,
5-3
integer,
6-1
number,
2-5
CaNT command,
4-2, 11-8
Conventions, manual, 1-2
Conversational language,
1-2
Comma (,),
2-4, 3-38, 3-39, 9-19
10-7
Commands,
1-3
Comments,
3-1
COMPILE command,
11-12
CTRL key,
1-5
CTRL/B, 11-19
CTRL/C, 1-6, 11-18
CTRL/O,
11-18
CTRL/P,
11-19
CTRL/U,
11-18
CTRL/Z, 11-19

DATA statement,
3-5, 3-33, 4-3
5-7, 10-1
Data storage,
7-1
DATE$ function,
5-10, 9-21
DEASSIGNED command,
11-16
Debugging,
4-1
DEF statement,
4-3
multiple line,
9-1
single line,
3-25, 5-9, 6-2
DELETE command,
11-6
DET,
8-6
Device buffer sizes,
7-2
Device codes,
11-16
Devices,
I/O,
7-1
DIM statement,
3-17, 4-3, 5-3,
7-8, 10-11
Disk random access data storage, 7-8
Dollar sign ($),
2-4, 5-1, 5-2, 7-1
DSK: ,
7-1, 7-2
DTAn:,
7-1, 7-2
Dummy variables,
3-26
Editing user program,
11-5
END statement,
3-42
EQV ,
2-9
ERR,
9-5, 9-6
ESCAPE key,
1-5, 11-17
Example programs,
2-2, 3-36, 7-11,
9-8
Exclamation mark (!),
2-4, 3-1,
9-17, 10-7
Exponentiation,
L-I, 2-8
Expressions,
2-5
Extension, file name,
7-2
External data storage,
7-1, 7-8
File #~,
7-5
File deletion,
7-13
File name specification,
7-1, 7-3
default device,
7-4
Files, reopening,
7-7
File storage,
7-1
FNEND statement,
4-3, 9-1
FOR modifier,
9-14
FOR statement,
3-12, 4-3
FOR-UNTIL statement, 9-11
FOR-WHILE statement,
9-11
Functions
integer, 3-22,
mathematical,
3-20
string,
5-9, 5-10
user defined,
3-25, 9-2

I-I

3-6, 4-3
GOTO statement,
3-31,4-3
GOSUB statement,

HELLO command,

1-4, 11-1

LIST command,
1-5, 11-7
Logical operators,
2-9, 3-9
Loop,
3-10, 3-11
9-10
conditional termination,
nested,
3-14
LPT : ,
7 -1, 7 - 2

IDN,
8-4
IF modifier,
9-12
IF statement,
3-7, 3-16
IF-GOTO,
3-7
IF-THEN,
3-7
IF-THEN-ELSE,
9-8
Mathematical functions,
3-20
Immediate mode,
4-1
Mathematical operators,
2-7
restrictions on,
4-3
MAT INPUT statement, 8-3, 10-4
IMP,
2-9
from external devices,
10-4
Input devices,
7-7
MAT PRINT statement, 8-1, 10-8
INPUT statement,
3-6, 3-35, 10-2
to external devices,
8-2
character string,
5-8
MAT READ statement,
8-1, 10-1
external device,
7-3,9-20, 10-2 IO~IIMatrices,
3-17,8-1
printing of character strings, 3-35,
addition,
8-6
10-3
arithmetic,
8-5
INPUT LINE
column,
8-3
external device,
10-3
initialization,
8-4
statement,
5-8, 9-20
multiplication of conformable,
Integer arithmetic,
6-1
8-6
Integer constant,
6-1
row,
8-3
Integer functions,
3-22
scalar multiplication,
8-6
Integer I/O,
6-2
undimensioned,
3-18
Integer variables,
6-1
zero elements,
3-18, 8-1
Internal file designator,
7-1, 7-6,
MID function,
5-10
7-7, 7-8, 7-10
Mixed mode,
3-3
Intrinsic functions,
Modifiers,
9-12
character string,
5-10
multiple,
9-16
mathematical,
3-20
MSR:,
7-1
matrix,
8-6
Multiple modifiers,
9-16
print,
9-19
Multiple statement lines,
2-3,
system,
9-21
4-2
Introduction to programming,
1-1
to BASIC,
1-2
INSTR function,
5-10
NAME-AS statement,
7-12
INV function,
8-6
Nested IF statements,
9-9
Inversion of matrices,
8-6
Nested loops,
3-14
NEW command,
11-3
NEXT statement,
3-13, 4-3
KEY command,
11-15
NONAME,
11-3, 11-4
Keys, terminal
NOT,
2-9
CTRL,
1-5
NUM$ function,
5-10
CTRL/C,
1-6, 11-18
Numbers,
2-5
floating point,
2-7
CTRL/U,
1-6, 11-18
ESCAPE or ALT MODE,
1-5, 11-17
integer,
2-7, 6-1
LINE FEED,
1-6, 9-10
line numbers,
2-3
number of significant digits,
RETURN,
1-5, 11-16
RUBOUT,
1-5, 11-17
2-5
KILL statement,
7-13
scientific notation (E
format),
2-6
Number sign (#),
2-4, 7-3, 7-4,
LEFT function,
5-10
9-18, 11-1
LEN function,
5-10
LENGTH command,
11-13
OLD command, 11-4
LET statement,
3-2
mUltiple assignment,
3-4
ON-ERROR-GOTO subroutine, 9-4
omitting "LET",
3-3
disabling,
9-7
LINE FEED,
1-6, 2-3, 2-4, 5-2, 9-9,
ON-GOSUB statement,
9-3
9-10 J 10-1 '. 9 -2.0
ON-GOTO statement,
9-3
On-line operations, 1-4, 11-1
Line numbers,
1-1, 2-3, 2-7, 4-1
range,
2-1
use,
2-1
1-2

Operators,
arithmetic, 2-7
logical, 2-9
relational, 2-8
Operator precedence, 2-7
OPEN statement, 7-2, 7-5, 7-10,
10-9
OR,
2-9
Output devices,
7-6

RIGHT function,
5-10
RUBOUT key,
1-5, 11-5, 11-17
RUN command, 1-5, 11-8
RSTS-11 Manager's Guide, 1-1

Parentheses,
2-4, 2-8
Passwords, 1-4, 11-2
Percent sign (%), 2-4, 6-1
POS function,
9-19
Precedence of operators, 2-7
PRINT functions,
9-19
PRINT statement, 3-4, 3-37, 10-5
character strings, 3-40, 3-41,
10-5
external device,
7-3, 7-6, 10-6
10-7
formatting in columns,
3-38,
10-7
output rules, 10-6
tight packing,
3-39, 10-6
PRINT-USING statement, 9-17, 10-7
Priorities in IF statements,
3-10
Program debugging,
4-1
Programming, 1-1, 2-1
see example programs
Project-programmer numbers, 1-4,
7-12, 11-1
Protection codes,
7-12
PTP : ,
7 -1 , 7 - 2
PTR:,
7-1, 7-2
QUOTES (' and "),

2-4, 5-1, 5-7

Random access data storage,
7-8
RANDOMIZE statement,
3-24
Random number function,
3-23
Read protect,
7-13
READ statement, 3-5, 3-33, 5-7,
10-1
READY, 1-4, 3-42
Redimensioning matrices,
8-5
Relational expression, 9-8
Relational operators, 2-8, 3-8,
5-3, 5-4
Remarks,
3-1
REM statement,
3-1
RENAME command, 11-12
Renaming files,
7-12
REPLACE command, 11-12
RESTORE statement, 3-34, 10-2
RESUME statement, 9-6
RETURN key, 1-5, 4-3, 11-16
RETURN statement,
3-31

SAVE command,
11-9
Semicolon (i),
2-4, 3-39, 9-19, 10-7
Sign function,
3-21
Single statement on multiple
lines, 2-3
length limit, 2-4
SLEEP function,
9-21
SPACES function,
5-10
Spaces, 2-5, 5-4, 5-9, 9-19
Square brackets, 1-3
Statements, 1-3, 2-3
multiple statements on a
single line,
2-3
order of evaluation,
2-1, 2-3
single statement on multiple
lines, 2-3
Statement modifiers, 9-12
STEP value,
3-13
STOP statement,
3-42, 4-1
String functions,
5-9, 5-10
Subscripted variables,
3-16
Subroutines, 3-30
System library,
7-1
System status, 11-13
TAB function,
9-19
TAB key, 11-18
TAPE command, 11-14
Teletype, 1-3
Terminal, 1-3, 7-5
Terminal value of loop, 3-13, 3-15,
9-12
TIME function,
9-21
TIME$ function,
5-10, 9-21
Time-sharing, 1-2
.TMP, 7-2
Transposition of matrices,
8-6
TRN function,
8-6
Truth tables,
2-10, 3-9
TTY: ,
7 -1, 7 - 2
TTYn,
7-1, 7-2
Unconditional branch, 3-6
Undimensioned matrices,
3-16
UNLESS modifier, 9-14
UNSAVE command, 11-10
UNTIL modifier, 9-16
Up-arrow (t), 9-18, 10-7
User-defined functions,
3-25
integer, 6-2
number of arguments,
3-27
recursive,
3-27
string, 5-9

1-3

User programs,

11-3

VAL function,
5-10
Variables, 2-7
subscripted,
3-16
Virtual core, 10-12
Virtual core matrices
character string lengths,
7-9
default character string length, 7-9
DIM statement,
7-8
WAIT function,
9-22
WHILE modifier, 9-15
Write protect,
7-13
XOR,

2-9

ZER,

8-4

1-4

HOW TO OBTAIN SOFTWARE INFORMATION
Announcements for new and revised software, as well as programming notes,
software problems, and documentation corrections are published by Software
Information Service in the following newsletters.
Digital Software News for the PDP-8 & PDP-12
Digital Software News for the PDP-II
Digital Software News for the PDP-9/15 Family
These newsletters contain information appl icable to software avai lable from
DigitalIs Program Library, Articles in Digital Software News update the
cumulative Software Performance Summary which is contained in each basic
kit of system software for new computers. To assure that the monthly Digital
Software News is sent to the appropriate software contact at your insta Ilation,
please check with the Software Specialist or Sales Engineer at your nearest
Digital office.
Questions or problems concerning Digital's Software should be reported to
the Software Specialist. In cases where no Software Specialist is available,
please send a Software Performance Report form with details of the problem to:
Software Information Service
Digital Equipment Corporation
146 Ma in Street, Bldg. 3-5
Maynard, Massachusetts 01754
These forms which are provided in the software kit should be fully filled out
and accompanied by teletype output as well as listings or tapes of the user
program to facilitate a complete investigation. An answer will be sent to the
individual and appropriate topics of general interest will be printed in the
newsletter.
Orders for new and revised software and manuals, additional Software Performance Report forms, and software price lists should be directed to the
nearest Digital Field office or representative. U. S. A. customers may order
directly from the Program Library in Maynard. When ordering, include the
code number and a brief description of the software requested.
Digital Equipment Computer Users' Society (DECUS) maintains a user library
and publishes a catalog of programs as well as the DECUSCOPE magazine
for its members and non-members who request it. For further information
please write to:
DECUS
Digital Equipment Corporation
146 Main Street, Bldg. 3-5
Maynard, Massachusetts 01754

RSTS-ll user's Guide
PL-11-71-~1-~1-A-D

READER'S

COMMENTS

Digital Equipment Corporation maintains a continuous effort to improve the quality and usefulness
of its publications. To do this effectively we need user feedback -- your critica I eva luation of
th is manua I .
Please comment on this manual's completeness, accuracy. organization, usabil ity and readability.

Did you find errors in this manual?

If so, specify by page.

How can th is manua I be improved?

Other comments?

Please state your position.
Name:

--------------------------------------------------------

-----------------------------------------------

Street:

Department:

----------------------------------------------------------City:

Organization:

------------------------------.

State:

Date:

--------------------

------------------------------------------

------------------------------------------------

--------------------------

Zip or Country

---------------

- - - - - - -

- - -

- - - - - - - - - -

- - - -

Fold Here - - - - - - - - - - - - - - - - - - - -

- - Do Not Tear - Fold Here and Staple -

- -

FIRST CLASS
PERMIT NO. 33
MAYNARD, MASS.
BUSINESS REPLY MAIL
NO POSTAGE STAMP NECESSARY IF MAILED IN THE UNITED STATf-S

Postage will be paid by:

mamaama
Digital Equipment Corporation
Software Information Services
146 Main Street, Bldg. 3-5
Maynard, Massachusetts 01754