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Document:	F77langRf Jul83
Order Number:	AA-V193A-TK
Revision:	0
Pages:	236
Original Filename:	AA-V193A-TK_F77langRf_Jul83.pdf

OCR Text

PDP-11 FORTRAN-77
Language Reference Manual
Order No. AA-V193A-TK

July 1983

This document describes the syntax and semantics of the FORTRAN-77
implementation of PDP-11 FORTRAN.

It does not, however, present infor-

mation specific to any operating system.

SUPERSESSION/UPDATE INFORMATION:

This is a new manual for this
release.

OPERATING SYSTEM AND VERSION:

RSX-11M V41
RSX-11M-PLUS V2.1
RSTS/E V8.0

VAX/VMS V3.2
SOFTWARE VERSION:

FORTRAN-77 V5.0

digital equipment corporation - maynard, massachusetts

First

Printing,

July

1983

The information in this document is subject to change
without
notice
and
should
not
be
<construed
as
a commitment by Digital Equipment
Corporation.
Digital Equipment Corporation assumes no
responsibility
for

any

errors

that

may

appear

this

document.

The
and

software described in this document is furnished
may
be
wused or copied only in accordance with

under
a
1license
the terms of such

license,.

responsibility

equipment that
affiliated

assumed

for

the

use

is not supplied by Digital

companies.

reliability

software

Equipment Corporation or

its

Rights

Printed

Reserved.

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The postpaid READER'S COMMENTS form on the last page of this
document
requests
the user's critical evaluation to assist in preparing future
documentation.

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following

are

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Equipment

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DEC/MMS

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VMS

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DECSYSTEM=-20

PDP
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DECUS

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DECwriter

Corporation:

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with the local Digital subsidiary (809-754-7575)

Internal orders should be placed through the Software Distribution Center (SDC), Digital Equipment
Corporation, Northboro, Massachusetts 01532

ZK2402

CONTENTS

Page

PREFACE

ASSIGNMENT

STATEMENTS

ARITHMETIC

ASSIGNMENT

LOGICAL

ASSIGNMENT

bt b

e b

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.

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&
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&
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g
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®

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4
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e

°
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v
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¢

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€

¢
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o
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o
&
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&
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(T o
n

o
o
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o

(De
0
[ o

s
°
*
.
'Y
L3
*
[)
Y

¢
©

[2
=~

J
o
o
o
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STATEMENT

iii

Arithmetic Expressions .
Use of Parentheses . .
Data Type of an Arithme
Character Expressions
Relational Expressions
Logical Expressions
.

e o

o'o"O.‘-o.

¢«

SUBSTRINGS

EXPRESSIONS

Array References Without
Adjustable Arrays
. . .
CHARACTER

o
s

Array

(D o

.
.

Type

.
.

Storage

[NNe
=1
T e
n
Q s

Implication

Data

Declarators

Subscripts
Array

by
«

(T e

Array

Typing

&«
o
o
o
&
Specificatio

Constants

Hollerith

VARIABLES
.
&
¢
Data Typing by
.

o
4
o

o
2
o

Real Constants .
.
. .
Double-Precision Constant
nts
Complex Constants
.
. .
.
Octal and Hexadecimal Const a n
Logical Constants
. .
Character Constants ..

[

(T
e

o
.

Constants

[Tle
x

NAMES

Integer

Data

[

COMPONENTS

TYPES

ARRAYS

STRUCTURE

STATEMENT

[

INCLUDE

Indicator

.
.
Field

Number

UNIT

Sequence
PROGRAM

Continuation Field
Statement Field
.

CONSTANTS

Indicators

Comment

SYMBOLIC

[NS

Field

Debugging-Statement

DATA

AU
W N

Formatting

Label

Statement

WwWwwWw

Tab-Character

Formatting
tin

e b
|

LINE

Character-per-Column

FORTRAN

Set

[)

[

Comments

Character

[]

Statements

.
.

OVERVIEW

WOOOONJIJJAAUNHDWWW

FORTRAN=-77

wWN
-

PDP-11

ELEMENTS

FORMATTING

AUV

MdbwwwwwwwwwhphdDd
-

PROGRAM

STATEMENT
NSNNNNNNOOM
OO
Na e RWWWWWWWwW WN -

NNNMNNNNNONMDNNNNNNOMDNNMDODMODNDNNDNNNDNDNDNDNDND
ww
W

CHAPTER

LANGUAGE

CHAPTER

INTRODUCTION

CHAPTER

STATEMENT

CONTROL

.
S
I
L
O

N
G
O~
I
i

i
A
A

STATEMENTS

STATEMENT

DECLARATION

STATEMENTS

Numeric Type Declaration St atements
Character Type Declaration Statements
DIMENSION
COMMON

STATEMENT

VIRTUAL

STATEMENT

Restrictions

Virtual

Array

EQUIVALENCE

HOWLWOAUMd
LS WNDNDN

L]
[
[
o
e
.
[
[

¢«

auoononnng
G,y
i
1
= OWONWUM
D WWN

IMPLICIT

STATEMENT

END

.
.

PAUSE STATEMENT
STOP STATEMENT .

pPs

STATEMENT

[]

LoopsS

STATEMENT

TYPE

.«

[}

[

Control

Iteration

STATEMENT

¢«

Arithmetic IF Statemen
.
Logical IF Statement . . .
Block IF Statements
.
. .
Statement Blocks . . . .
Block IF Examples
. . .
Nested Block IF Consructs

Using

Virtual

References

STATEMENT

Arrays

Subprogra ms

.«

STATEMENT

ARGUMENTS

PARAMETER

PROGRAM
BLOCK

STATEMENT

DATA

[)

L]
L4

L4
[]

L]
L4

A4
L]

£
L

in Function Subprog rams

Statement

ENTRY

4
4 .1

.
.
.

Statement Functions
.
Function Subprograms .
Subroutine Subprograms

USER-WRITTEN

SUBPROGRAMS

1
2
3

Rules Governing Subprogram Arguments
Adjustable Arrays
. . . .
Assumed-Size Dummy Arrays

AN
i
|
i
I
I
NHEOJAUTH N

.
.

STATEMENT

(o) W0 )

¢«

INTRINSIC
DATA

STATEMENT

SAVE

EXTERNAL

Making Arrays Equivalent .
Making Substrings Equivalen t
Extending Common Blocks
.

N
W

RETURN

Statement

CONTINUE

WN
-

.
Ld

CALL

L]
.

Control Transfers
Extended Range .

L]
L4

STATEMENTS

Nested

W N

.
-

¢«

W N

*
s
.

o
o
s

Assigned

wn
9
&
o
*»
o
«

Stateme nt
.

HEFRFFRFOOJOASTAANNUVTUNTUTE
WN NN KK
.
.
«
s
o
wN
= O

o
e

¢«

Statement

SUBPROGRAM

SUBPROGRAMS

.+«

GO TO

NDNDNE

Computed

2)]

oottty
n

STATEMENTS

Unconditional

(o)W e We Mo Mo We) We) Mo We)We))

CHAPTER

STATEMEN T

LABELS

STATEMENTS

SPECIFICATION

CHAPTER

WWwwwN =

®
s
8

Y-

it~

ASSIGNMENT

ASSIGNING

LCONOAUTBWWWWWRNNONNDNDDNDNDOND
R

CHARACTER

3.4

CHAPTER

3.3

CONTENTS

ENTRY

INTRINSIC

6-13

FUNCTIONS

6-13

.
.

6-14

Intrinsic

and

Usage

6-15

Character
Functions

and Lexical Comparison
L] L] L . L
* - L L ® L4

Generic

Function

6-13

Library
Ll

o
.«
¢«
.
o

o
.
¢
«
o

o
«
¢
&«
o

o
«
o
«
o

o
«
«
.«
o

&
.
&
.
o

.1.4

Access

L]
.
L)

.
[)

[

L]
[}
.

w
N -

Sequential READ Statements
The Formatted Sequential READ Statement
The List-Directed READ Statement

The

Unformatted

Direct

The

Access

Formatted

The

Sequential
e

READ

Direct

7-15
7-15

RE AD

7-17

Statements
Access

READ

Direct

Unformatted

¢
¢
&
o
®

[

STATEMENTS

&
.
.

Spe01f1ers

o
.
.

READ

RULES

Transfer-of-Control

.
.

4
o

I/O List . . + + ¢
Simple List
. .
Implied DO List

The
°

The

N NN

.
.

@
*

AN
D WN [\

°«
L]

I/0 STATEMENT COMPONENTS
The Control List .
.
. .
Logical Unit Specifier
Internal File Specifier
Format Specifier .
.
.
.
Record Specifier .
.
.
.
Key Specifier
.
.
.
.
.

THE

*
L]
[]
[]
e

L]
[]
L]
*

.
.

SYNTACTICAL

BB B

D
D

g
N

NANSNNNNNNNNS

Access

Statement

LAauuuonoog.b
&b

Sequential Access
Direct Access
. .
Keyed

o
.
.«
.
o

Modes

NN NNNSNNSNNN
1
{

o
.
.
.
¢

4.3

4.1
4.2

W
N
HFONNNOOOVIUUUbaDdWWWWHNN

Files
. & ¢ & o o o o o o
Sequential Organization
Relative Organization
.
Indexed Organization . .
Internal Files . . & ¢ ¢« ¢«

Records

1.2
.1.2.1
1.2.2
.1.2.3
.1.3

1.1

NN
N
A
N
N
N

STATEMENTS

S WNNONNNNNNNN
R
e
b

Subprograms

LIBRARY

.
.

INPUT/OUTPUT

NN NUNNNSNNNSNNNNNSNNNNNNEN
N NNNNNNNS

OTHER

Intrinsic Function References
Generic Function References
.

1
2

7-18

Statement

Access

7-18

READ

o
o
o
9
o
o
o
o

~NSNoooooomuioahan

Formatted

Unformatted

The

W N

o
o

o
e
¢

Statements

The

Internal

WRITE

Indexed

READ

Indexed
.

¢«

.«

7-19

Statement

READ

Statement

STATEMENTS

Statement

The

1
2

Indexed

.
&

7-23

The
The
The
THE

REWRITE

The

THE

WRITE

Statement

STATEMENT

Indexed

The
The

Statements

Formatted Indexed WRITE Statement
Unformatted Indexed WRITE Statement

Internal

REWRITE

Statement

Formatted Indexed REWRITE Statement
Unformatted Indexed REWRITE Statement

STATEMENT

7-23
1-24
7-24
7-25

7-26

7-27
7-27

WRITE

7-20

7-21
7-21

The Sequential WRITE Statements
The Formatted Sequential WRITE Statement
The List-Directed WRITE Statement
The Unformatted Sequential WRITE Statemen t
The Direct Access WRITE Statements
The Formatted Direct Access WRITE Statement
WRITE
Direct Access
The
Unformatted
Statement

READ

The

L]
*

Indexed

oW
w W

The

THE

[ ]

7-19

NNNNNNNAGN

CHAPTER

Subroutine

AND

.«

7-27
7-28
7-28

7-29
7-29
7-30
7-30
7-30
7-31

CONTENTS

THE

TYPE

FORMAT

AND

7-31

STATEMENTS

—QPP TT T T TTT T TO . R c3I PR & CLOXDOu O

<<«CONELo bt

CHAPTER

7.8

(PCTMoEHI@eO5SRt<

L ]

gX 4+

Le&o4@

eo*[, (e&o°i eo*, Eo+ o4 eo 2eo eo¢l

AUXILIARY
O

INPUT/OUTPUT

ovooOo'.o-.oo-

L 2

L 4

)

1951

STATEMENTS

0Oor~rr~oo0
OOOO

BRe

24 =

CHAPTER

O~ 3 e

W00 o

~MN

}
s =[«
F] > E

]

o o ¢ ey

30 mo
Jm0o D=[ o
163] Ow o1=

(SRd)]=L

®* o
e
L]
NN
SSNd WO W

CONTENTS

9.
9.

9-12

RECORDTYPE

9-13

SHARED

9-13
9-14

STATUS

TYPE

UNIT

USEROPEN

9-14
.

STATEMENT

REWIND

STATEMENT

BACKSPACE
DELETE

Sequential
Direct
UNLOCK

STATEMENT

AND

DEFINE

SN b WN

THE

B.
B.

C.
cC.
C.

FILE

PARAMETER

9-14

9-15

9-16
9-17
9-17
9-18

.
.

9-18

¢«

9-19

STATEMENTS

«
.

INTEGER

o«

CONSTANTS

THE

EXTERNAL

STATEMENT

SETS

CHARACTER

SET

RADIX-50

CONSTANTS

LANGUAGE

SUMMARY

AND

CHARACTER

SET

Range

EXPRESSION

OPERATORS

STATEMENTS

LIBRARY

9-18

ELEMENTS

DECODE

Statement

INTERPRETATION

FORTRAN

ASCII

STATEMENT

FORMS

/NOF77

STATEMENT

CHARACTER

W N+~

ENCODE

OCTAL

Statement

FIND

DELETE

STATEMENT

ENDFILE

STATEMENT

APPENDIX

o
.

LANGUAGE

APPENDIX

ADDITIONAL

WIN
=

APPENDIX

9.
9.
9.
9.
9.
9.
9.
9.
9.
9.

RECORDSIZE

SNAVTUNT TS WN

9.
9.

R e b s

RECL

FUNCTIONS

INDEX

112~

44~
4-

FORTRAN Coding Form
. . . .
Line Formatting Example
. .
Required Order of Statements

. .
. .
and

Array

Storage

Examples
Nested
Control

Block

LooOpsS

Transfers

o
and

Extended

Equivalence of Arrays with Nonunity Lower Bounds
Equivalence of Substrings
. . .
Equivalence of Character Arrays
Multiple Functions in a Function Subprogram
Multiple Function Name Usage . .
Variable Format Expression Example . .

6—
8-

Storage

6—

Array

Constructs

Equivalence

55—

HF N

FIGURE

R WND -

FIGURES

vii

CONTENTS

List-Directed Output Formats . . . . .
Effect of Data Magnitude on G Formats
Default Field Widths . . . . .
Carriage Control Characters
.
Summary of FORMAT Codes
. . .

&
.
.
.

.«

Generic

and

Intrinsic

viii

.
.

.
«

«
«

¢
o

Functions

¢
o

o
o

¢
o

o
o«

@
&

©®
o
®

o
e

) O

ASCII Character Set
Expression Operators

OPEN Statement ‘Keyword Values
. . .
.
Allowed Combinations of ACCESS Values
. .
Valid Access Modes for ORGANIZATION Keyword

OFNNAWWDWHFERFOMALAENVION
W LN

Types

o))
N
0 0
|
I NSl
ow il o
[
I =
NN

Data

0wl

Exponentiation

Conversion Rules for Assignment Statements
Types of User-Written Subprograms
. . . .
Generic Function Name Summary
.« « « ¢ « &
Available I/0 Statements . . « ¢ ¢ &+ ¢ o &
Access Modes for Each File Organization
.

.
.

QOwl

.
.

Entities Identified by Symbolic Names
Data Type Storage Requirements . . . .

[

NHFFWNHEBWNHFWNENEFWND
-

QOQPDOWOUOWOOOOIIIOATWNNDDND

TABLES

PREFACE

MANUAL

OBJECTIVES

This

manual

describes

the

PDP-11

FORTRAN-77

systems

that

run

the

elements

language

the

PDP-11

reference
family

FORTRAN-77

manual

for

computers.

specific
to
any operating system is presented here.
on a particular operating system, refer to the user's
system

INTENDED

Readers

the

who

have

will

STRUCTURE

manual

basic

derive

THIS

User's

operating

information

For information
guide
for
that

Guide.

understanding

maximum

benefit

from

the

this

FORTRAN

nine

chapters

and

three

appendixes.

Chapter 1 consists of general
information
FORTRAN-77
and
introduces
basic
facts
FORTRAN-77

Chapter

programming

manual.

DOCUMENT

contains

PDP-11

FORTRAN-77

serves

AUDIENCE

language

This

PDP-11

and

several

PDP-11
writing

programs.

describes

statements,

concerning
needed
for

the

including

components
symbolic

PDP-11

names,

FORTRAN-77

constants,

and

variables.
e

Chapter
used in

Chapter 4 discusses control statements, which
from one point in the program to another,

transfer

Chapter

which

3
a

describes
program.

assignment

describes

specification

characteristics
of
symbols
type and array dimensions.
e

Chapter

supplied

discusses
with

subprograms,

PDP-11

1in

both

PDP-11

Chapter 8 describes the FORMAT
with formatted I/0O statements.

statements

Chapter

such

OPEN,

FORTRAN-77

information

CLOSE,

program,

user-written

contains

define

values

control

define

such

and

the

data

those

FORTRAN-77.

Chapter

discusses

which

statements,

used

statements,

and

input

and

used

auxiliary

output

(1/0).

conjunction

I/0

statements,

ENDFILE.

Appendix A describes some
statements
and
language
that
provide compatible support for programs written
versions of PDP-11 FORTRAN.

features
in older

PREFACE

Appendix B summarizes the character sets supported

PDP-11

FORTRAN-77.

elements

language

the

summarizes

Appendix

PDP-11

FORTRAN-77.

ASSOCIATED DOCUMENTS

The

documents

following

are

interest

FORTRAN-77

PDP-11

programmers:

FORTRAN-77 User's Guide

PDP-11

PDP-11 FORTRAN-77 Object Time System Reference Manual

PDP—ll_FORTRAN—77

Installation Guide/Release Notes

CONVENTIONS USED IN THIS DOCUMENT

The

following conventions are

used

this manual:

in examples indicate that you

VUppercase words and letters used

Lowercase words and letters used in examples indicate that you
are to substitute a word or value of your choice.

Brackets

the words and

type

should

enclose optional

([])

shown.

elements.

enclose lists from which

({})

Braces

letters as

one

item

can

element

chosen.

(...)

An ellipsis
repeated

In addition,

the

one

indicates that the

following

characters:

Tab character
(@B

Space character

preceding

times.

characters

denote

special

nonprinting

CHAPTER
INTRODUCTION

1.1

LANGUAGE

The

PDP-11

Standard

FORTRAN-77
to

1language

subset

the

FORTRAN-77

FORTRAN
as
to obtain a

American

Standards

York

National

You

can

use

If
the
integer
e

subset

the

American

X3.9-1978),

standard,

and

National

DIGITAL-supplied
certain

features

defined
by
the
ANSI
Standard.
copy of the ANSI standard, write to

Institute,

enhancements

any

Inc.,

1430

Broadway,

New

For
the

York,

the

FORTRAN-77

array

standard

expression

not

type,

converted

expressions

can

contain

elements

any

data

integer

subset

subscript.

type.

type

character.

The

LOGICAL*1

The

IMPLICIT

symbolic

The

arithmetic

expression

Mixed-mode
except

(ANSI

10018.

The DIGITAL-supplied
follow:
e

FORTRAN-77

comprises

lanquage

of
full-language
information on how
New

PDP-11

OVERVIEW

FORTRAN-77

enhancements

and

LOGICAL*2

statement

data

types

redefines

the

have

been

implied

added.

data

type

names.

following

input/output

(I/0)

statements

have

been

added:

TYPE

Device-oriented

I/0

READ
WRITE
FIND

(u'r)

Unformatted

direct—-access

1I/0

(u'r)

READ

(u'r,fmt)

WRITE

(u'r,fmt)

Formatted

DEFINE

FILE

File

direct-access

control

I/0

and

specification
ENCODE
DECODE

READ

(u,f,key)

READ

(u,key)

Formatted data
in memory

Indexed

1/0

REWRITE

DELETE

Record

UNLOCK

and

control

update

conversion

attribute

INTRODUCTION TO PDP-11 FCRTRAN-77

You can

include an explanatory comment on the same line as any

with an exclamation point

begin

comments

These

statement.
().

placing
by
You can include debugging statements in a program
These statements are compiled only
1letter D in column 1.
the
otherwise,
qualifier;
command
compiler
when you specify a
they

are

You can
in

the

treated

comments.

use any arithmetic
computed

GO TO

expression as

the control

parameter

statement.

Virtual

arrays provide

program

address

large

data

areas

outside

normal

OPEN,

CLOSE,

space.

You can include the specification ERR=s in

any

DELETE, UNLOCK, BACKSPACE, REWIND, or ENDFILE statement
FIND,
to transfer control to the statement specified by
s
when
an
error

condition occurs.

The INCLUDE statement incorporates FORTRAN statements
from
separate file into a FORTRAN program during compilation.

The INTEGER*4 data
You can use octal
numeric

type provides a sign bit and 31 data bits.
and hexadecimal

constants

place

Double-precision

Function

forms,

function

FORTRAN-defined

control

real

data

£features

types

including

LEN,

including

double-precision

including

ICHAR,

and

INDEX

S§,SP,SS,T,TL,

selection based on

argument

and

data

type

for

functions

double-precision

variable

statement

variable

Use
of
any
increment, or

Use

complex

edit descriptors,

Generic

and

subprograms,

Exponentiation

any

use
character
substrings
and
all
the
character
functions defined in the full language except CHAR.

In addition, PDP-11 FORTRAN-77
includes
the
following
full-language FORTRAN as defined by the ANSI Standard:

Use

constants.

You
can
intrinsic

Format

and

OPEN

the

transfer

arithmetic
final value

expression
as
the
in a DO statement.

1initial

wvalue,

statements

specification

control

the

ERR=s

statement

READ or

WRITE

specified

statements

by s when

an error

occurs

Use of
format

list-directed
specification

1/0 to

Use

constants

expressions

REWRITE,

TYPE,

and

perform

statements

formatted

the

I/0

1I/0

1lists

without

WRITE,

INTRODUCTION

Specification

lower

PDP-11

bounds

FORTRAN-77

for

array

dimensions

array

declarators

1.2

Use of ENTRY statements in SUBROUTINE
to define multiple entry points

Use of
PARAMETER
constant values

PROGRAM

statements

1.2.1

subprograms

symbolic

names

ELEMENTS

FORTRAN programs consist of statements
statements
are
organized
into
program
sequence
of
statements
that
defines
a

terminates

FUNCTION

assign

All

program
program

and

with

END

statement.

and

optional comments.
wunits.
A program unit
computing
procedure

program

unit

or a subprogram.
An executable program
and one or more optional subprograms.

can

consists

either
of

one

The
is a
and

main
main

§Statements

Statements

are
grouped
into
two
general
classes:
executable
and
nonexecutable,
Executable
statements
specify
the
actions
of
a
program;
nonexecutable
statements
describe
data
arrangement
and
characteristics, and provide editing and data-conversion information.
Statements are
a string of up

one

line,

divided into physical
to 80 characters.
If
can be continued on one

continuation

lines.

continuation

information

character

sections called lines.
a statement is too long
or

continuation

the

continuation

sixth

characters,

additional

1line

column

see

A line is
to fit on
lines,
called

1is

that

Section

identified

line.

(For

further

1.3.4.)

You can identify a statement with a label to enable
other
statements
to
reference
it:
that
1is,
either to transfer control to it or to
obtain the information it contains.
A statement label is
an
integer
number placed in the first five columns of a statement's initial line.
Any statement can have a label;
however, only executable
and
FORMAT
statements can be referenced with a label.

l1.2.2

Comments

not

affect

a
documentation
aid.
freely to describe the

program

processing

You
can,
actions
of

and
a

any

way;

they

are

are encouraged to, use
program,
to
identify

merely

comments
program

sections
and
processes,
and
to
facilitate
the
reading
of
source-program listings.
The letter C or an asterisk (*)
in the first
column
of
a
source
1line
identifies
that
1line
as a comment.
1In
addition, if you place an exc¢lamation point (!) in
any
column
of
a
line
except
column 6, the rest of that line is treated as a comment.
(However, if you place an exclamation point in column
6
of
a
line,
that line will be treated as a continuation line.)
Any

printable

character

can

appear

comment.

INTRODUCTION

1.2.3
The

Character

PDP-11

FORTRAN-77

Set

FORTRAN-77

All

TO PDP-11

character

uppercase

and

set

consists

of:

letters

lowercase

through

z)
2.

The

numerals

through

The special characters listed below:
Character
A or

Name

(A8

Space

tab

Equal

sign

Plus

Minus

Asterisk

Slash

(

Left

)

Right

Comma

Period

Apostrophe

sign
sign

parenthesis
parenthesis

Quotation
S

Dollar

mark

sign

Exclamation point

Other

Colon

Left

Right

printable

ASCII

characters

can

angle

Except

character

1.3

between

and

Hollerith

uppercase

FORMATTING

A FORTRAN

FORTRAN

has

Every

line

statement

A continuation-indicator

FORTRAN
(see

the

lowercase

letters.

fields:

constant

constants,

LINE

four

label

and

bracket

appear

only
as part of a character or Hollerith
a list of printable characters).

distinction

bracket

field

statement

Appendix

compiler

for

makes

INTRODUCTION

You

statement

field

®¢

sequence

number

can

per

format

column

FORTRAN

PDP-11

FORTRAN-77

field

line

two

(character-per-column

ways:

typing

formatting);

conjunction

one

character

using,

with character-per-column formatting,
the
tab
character
(tab-character
formatting)
to
get from field to field.
You can use
character-per-column formatting when
punching
cards,
writing
on
a
coding
form,
or
typing
on
a
terminal
keyboard;
you
can
use
tab-character formatting,
terminal keyboard.

l.3.1

Character-per-Column

shown

fields:
and

each

Each

however,

Figure

1-1,

statement

sequence

column

represents

you

are

typing

FORTRAN

single

get

space,

from

one

into

which

field

can

another,

placed

you

type

space individually until you arrive
at
the
correct
position.
example,
in
Figure
1-1,
to enter the comment, after typing 'C'
press the space bar five times and then begin typing the comment.

FO RTRAN

)

CODEr

CODING FORM

C Comment

STATEME{NT

t2343

+
+

FORTRAN STATEMENT

IDENTIFICATION

|
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77 PUPR

DIGITAL

line is divided into
four
separate
continuation indicator, statement text,
(Sections 1.3.3 through 1.3.6 describe the use

number.

character.

when

Formatting

label,

field.)

single

only

EQUIPMENT

CORPORATION

MAYNARD,

MASSACHUSETTS

ZK-203-81

Figure

1-1:

FORTRAN

Coding

Form

each
For
you

INTRODUCTION TO PDP-11

FORTRAN-77

Field
Statement

Column(s)

label

Continuation

indicator

l1.3.2

Tab-Character

through

Statement
Sequence

through

7
number

through

Formatting

You can press the tab character to move to the
continuation-indicator
field
from
the statement label field, or to the statement field from
the continuation-character field;
however, you
cannot
move
to
the
sequence-number
field
by
using
the
tab.
Figure
1-2
compares
keystrokes in lines typed with tab-character formatting with those
in
lines typed with character-per-column formatting,

Format Using TAB Character

Character-per-Column Format

5|6}7

10|11

13 14

15616

C @8 FIRST VALUE

FIHIR|S|T

VIA|L

0@
| = J + 5«K
+

1]0

L*M

@B IVAL = I+2

1718

19 20

|UI|E

5[+

Lf=IM

I |[V]A]|L

I |+12

ZK-204-81

Figure

1-2:

Line

Formatting

Example

In tab-character formatting, the statement-label field consists of the
characters you type before you type the first tab character;
however,
the statement-label field cannot have more than five characters,
After you type the
first
tab
continuation-indicator field or

character,
a statement

To enter a continuation-indicator field,
statement
field
then
consists
of all
this digit, to the end of the line.

you
<can
field.

enter

either

you
type
any
digit;
the characters you type

the
after

To enter a statement field without entering
a
continuation-indicator
field,
you simply type the statement immediately after the first tab.
(No FORTRAN statement can start with a digit.)

INTRODUCTION TO PDP-11 FORTRAN-77

Many text editors and terminals advance the terminal print carriage to
a
predefined print position when you type the TAB key.
However, this
action
is
not
related
to
the
PDP-11
FORTRAN-77
compiler's
interpretation of the tab character described above.
If you use the tab character to improve the legibility
of
a
FORTRAN
statement, the spaces introduced into the statement are ignored by the
compiler but are printed in a source listing.
Tab
characters
in
a
statement

listing, a
the
next
forth).

l1.3.3
A

field
are
ignored
by
the compiler as well.
1In a source
tab causes the character following the tab to be printed at
tab stop (which is located at columns 9, 17, 25, 33, and so

Statement

statement

the

Label

label,

statement-label

leading

are

Any

statement

two

statements

You

can

use

Field
number,

field

ignored.

(An

referenced
within

two

special

consists

all-zero
another

program

statement's

indicators

statement

unit

can

have

the

five

initial

decimal

line.

label

must
the

have
same

£first

digits

Spaces

and

invalid.)
a

1label.

label.

column

1label

field:
the
comment indicator and the debugging-statement indicator.
These indicators are described in Sections 1.3.3.1 and 1.3.3.2.

The

statement

label

field

continuation

line

must

1.3.3.1
Comment Indicators - The letter
C
or
an
column
1
of
a line indicates that the entire line
exclamation point (!)
in
any
column
of
a
1line
indicates
indicate

that

the

blank

comment.

The compiler
then ignores

prints
it.

remainder

comment

line

the

line

blank.

asterisk
(*)
1in
is a comment.
An
except
column
6

comment.

source-—-program

All

blanks

1listing

and

1.3.3.2
Debugging-Statement Indicator - The letter D in column 1 of a
line
designates
the
contents
of the statement field as a debugging

statement.
A debugging-statement line can have a statement
1label
in
the
four
remaining
columns
of
the
1label
field.
If a debugging
statement is continued tc one or more other lines, every
continuation
line

must

have

column

and

continuation

indicator

column

Debugging statements are
not
compiled
wunless
you
use
a
compiler
command
to
specify
that
they
be
compiled.
1If you do not specify
debugging-statement compilation, any debugging statements are
treated
as comments.
For a description of the available compilation commands,
refer to the PDP-11 FORTRAN-77 User's Guide.

1.3.4

Continuation

Field

A continuation indicator is any
column 6 of a line, or any digit
A

statement

can

divided

into

character
(except 0)
continuation

(except
0
or
the first

after

lines

any

space)

tab.

point.

INTRODUCTION

PDP-11

FORTRAN-77

The compiler considers the characters after the continuation character
to follow the last character of the previous line, as if there were no
physical breaks at that point.
If a continuation indicator is 0,
the
compiler
considers
the
1line containing it to be the first line of a
statement.

Comment lines cannot be continued.
They can, however, occur between a
statement's
initial
1line
and
1its
continuation
1line or lines, and
between successive continuation lines.

1.3.5

Statement

Field

The text of a statement is placed in a statement field.
Because
the
compiler
ignores
all
tab characters and spaces in a statement field
except those in Hollerith constants and alphanumeric literals, you can
space
the text in a statement field in any way you desire to maximize
legibility.
The use of tabs
for
spacing
1is
discussed
1in
Section
1.3.2.

NOTE

If
a
1line
extends
beyond
character
position 72, the text following position
72 is ignored;
no
warning
message
1is
printed.

1.3.6

Sequence

Number

A sequence number or
columns 73 through 80
this field.
Remember

that

tab--character

1.4

PROGRAM

you

Field
other
of any

cannot

identifying
information
can
appear
line;
the compiler ignores characters

in
in

move

the

sequence-number

field

formatting.

UNIT

STRUCTURE

Figure
1-3
shows
the
allowed
order
of
statements
in
a
PDP-11
FORTRAN-77
program
unit.
In
this
figure, vertical lines separate
statement types that may be interspersed with one another -- that
is,
occur in any order relative to each other.
For example, comment lines
and

FORMAT

statements

statements
of

be
For

and

may

executable

occur

before,

statements

(see

between,

paragraph)

body

the

program.
Horizontal lines indicate statement types
that
cannot
interspersed but must occur in a prescribed order within a program.
example,
or

IMPLICIT

after

statement

END

cannot

occur

before

ELSE,

ACCEPT,

OPEN,

ENDIF,
FIND,

CLOSE,

CONTINUE,
DELETE,

CALL,

declaration.

COMMON,

STOP,

PAUSE,

REWRITE,

RETURN,

‘"specification"

DIMENSION,

PROGRAM

1-3
block

include:
IF, ELSE

statement.

The
"executable"
statements
mentioned
in
Figure
assignment,
ASSIGN,
GOTO,
arithmetic IF, logical IF,

The

DATA

statement

IF,

after

and

DO,

READ,

BACKSPACE,

WRITE,

ENDFILE,

PRINT,

REWIND,

TYPE,
UNLOCK,

END.

statements
EQUIVALENCE,

mentioned
EXTERNAL,

Figure

INTRINSIC,

1-3
SAVE,

include:
and

type

INTRODUCTION

PDP-11

FORTRAN-77

PROGRAM, FUNCTION, SUBROUTINE, or BLOCK DATA Statements

IMPLICIT
Statements
PARAMETER

Other
Comment

Statements

Specification

tnes

FORMAT

and

INCLUDE

Statements

and

Statements

ENTRY

Statements

Statement Function

DATA

Definitions

Statements

Executable

Statements

END Line
ZK-205-81

Figure

1.5

The

INCLUDE

are

1-3:

Order

specifies

that

incorporated

statement.

INCLUDE

The

statement

INCLUDE
INCLUDE

Statements

the

contents

and

Lines

STATEMENT

statement

Required

has

into

has

effect

the

compilation
on

program

designated

directly

following

file
the

execution.

form:

'filespec[/[NO]JLIST]'

filespec
A

file

specification

that

represents

file

specification

(See
the
PDP-11
specification.)

the

file

must

form
to

character

included

acceptable

FORTRAN-77

User's

to
Guide

the
for

constant

string

compilation.

This
system.

operating
the

form

file

The

/LIST qualifier specifies that the statements
in
the
designated
file
are
to
be
included
in
the
compilation
source listing;
an
asterisk (*) precedes each statement included.
The /NOLIST
qualifier
specifies
that
the
statements
1in the designated file are not to be
included in the compilation source listing.
The
default
1is
/LIST;
that
1is,
the
compiler
assumes
/LIST
if you do not specify either
qualifier,
When

the

compiler

statements

the

from

designated,

file,

the

statement,

encounters
the

included,

compiler

current

reads

INCLUDE
file

file.

the

and

When

statement,
begins

reading

reaches

statement

stops

reading

statements

the

after

end

the

from

this
INCLUDE

INTRODUCTION TO PDP-11 FORTRAN-77

An INCLUDE statement can be contained in an included file.

each
An included file cannot begin with a continuation 1line;
file.
single
a
within
contained
completely
be
statement included must
that

The INCLUDE statement can appear anywhere

comment

1line

can

appear.

Any PDP-11 FORTRAN-77 statement can appear in an included file;
however, all the statements in an included file, when combined with
the other statements in a compilation, must satisfy
in

shown

the

requirements

1-3.

Figure

In the following example, the included file COMMON.FTN defines the
size of the blank COMMON block and the size of the arrays X, Y, and Z.
File COMMON.FTN

Main Program File

INCLUDE 'COMMON.FTN'

DIMENSION Z (M)
CALL

CUBE

I=1,M

X(I)+SQRT(Y(I))

Z(I)

SUBROUTINE

INCLUDE
po

10,

X(I)

I=1,M

= Y(I)**3

RETURN
END

CUBE

'COMMON.FTN'

PARAMETER (M = 100)
,Y (M)
COMMON X (M)

CHAPTER
STATEMENT

PDP-11

FORTRAN-77

statements

Constants

cannot

changed

fixed

are

COMPONENTS

composed

values,

such

program

symbolic

These

can

changed

groups

values

that

Arrays

names

that

are

called

Function references -lists
of
arguments.
performs

a specified
trigonometric
sine)

represent

are

be
referenced
individually
subscript, or
collectively
by

values

components:
These

values

array

stored

values.

statements.

stored

contiguously

symbolic

name

and

with

name

only.

elements.

function names optionally
followed
by
A
function
1is
a
program
unit that

computation

(for
wusing
arguments
reference;
the resulting value is then
function reference.
Expressions

basic

numbers.

program

can

Individual

five

statements.

Variables -values

example,

supplied
used

computing

a
function

a
place

the

combinations

of
references,

constants,
variables,
array
and operators.
An operator is
a
unique
symbol
for
a
particular
operation
(such
as
multiplication)
that obtains a single result,

elements,

function

Variables, arrays, and functions have symbolic names.
is a string of characters that identifies an entity in
Constants,

following

variables,

data

arrays,

types:

expressions,

and

A symbolic
a program,

functions

can

have

name

the

Logical
Integer

Real
Double-precision

Complex
Character
Symbolic

names,

(except

data

function

references

are

for

types,

discussed

are
in

functions)

and

all

the

discussed
Chapter

statement

this

components

chapter;

except

function

STATEMENT COMPONENTS

2.1

SYMBOLIC NAMES

Symbolic names identify the entities that

can

appear

program

The entities that symbolic names identify are listed in Table
unit.
2-1, where the column labelled "Typed" indicates whether an entity has
(Data types are discussed in
a data type (such as real or integer).
Section

2.2.)

Entities Identified by Symbolic Names

‘Table 2-1:

Entity

Typed
Yes
Yes
Yes
Yes
Yes
No
No
No
No
Yes
Yes

Variables
Arrays
Statement functions
Intrinsic functions
Function subprograms
Subroutine subprograms
Common blocks
Main programs
Block data subprograms
Dummy arguments
Function entry points

‘Subroutine entry points
Parameter

Yes

constants

(letters and digits)
is a string of characters
A symbolic name
If
the first character must be a letter.
totaling a maximum of six;
automatically
will
system
the
used,
are
characters
more than six
truncate the name to six characters during compilation.
invalid symbolic names are:

Examples of valid and

Invalid

valid

(begins with a numeral)

NUMBER

(contains a special character)

B.4

the
is,
unit -- that
Symbolic names must be unique within a program
symbolic name cannot be used to identify two or more entities in
same
the

unit.

same program

In executable programs consisting of two

symbolic

name

throughout all

for

the

any

program units:

Intrinsic

functions

Function

subprograms

Subroutine

Common

Main

Block

Function entries

Subroutine

subprograms

blocks

programs

data

the

subprograms

entries

following

program

entities

units,

must be unique

STATEMENT

Therefore

if,

for

example,

one

function
named
UMP,
you
other entity anywhere else
separate program unit.

2.2

COMPONENTS

your

program

units

contains

cannot use UMP as the symbolic name for any
in
your
program,
even
1in
a
completely

DATA TYPES

Each
basic
statement
component
in
a
PDP-11
FORTRAN-77
program
(constant,
variable,
array,
function
reference, or expression) has
assigned to it one of six data types that specifies the kind of
wvalue
it can represent.
The data types and the values they represent are:
e

Integer

Real -decimal

for

decimal

fraction

Double

precision

for

Complex
number:
second

whole

number

a decimal number:
that
1is,
fraction,
or
a
combination of

many maximum
e

—-—-

for

for a pair
the
‘first

representing

Logical

Character

significant

for
--

the

for

number

with

whole
number,
whole number and

than

twice

a
a

real

of real numbers representing
a
complex
value
representing
the
real part, the

the

imaginary

value

real

digits

a
a

true

sequence

part

the

value

false

characters

The data type of a basic component can be assigned
in
one
of
three
ways:
it
can
be
inherent
in
the component's construction (as in
constants);
it can be implied by a naming convention (with or without
an IMPLICIT statement);
or it can be explicitly declared.
Whenever

value of

one

data

type

converted

type,
the
conversion
is
performed
assignment statements (see Table 3-1).
For

the

memory
data

purpose

type

These

PDP-11

FORTRAN-77

The

type
form

PDP-11

variations)

above,

data

facilitating

requirements,
data

addition

types

data

requires
*n

appended

are

types,

for

control

FORTRAN-77
to

the

well

value
to

six
in

Table

the

for

performance

and

data

data
2-2,

amount

another

rules

several

basic

the

processing

provides

included

according

types

types
which

(or

1listed

lists

memory

all
each

storage.

data

type

name

called

data-type

length

specifier.

2.3

CONSTANTS

constant represents
values true or false,
Octal,

hexadecimal,

constants
appear

assume

(see

the

Section

a fixed value and can be
or a character string.

and

Hollerith

data

type

2.3.8).

constants

prescribed

have

the

number,

data

context

the

1logical

type;

which

these

they

STATEMENT

Table

2-2:

Data

COMPONENTS

Type

Storage

Data Type

Requirements

Storage Requirements
(Bytes)

BYTE

LOGICAL

LOGICAL*1

LOGICAL*2
LOGICAL*4
INTEGER

INTEGER*4

REAL

REAL*4

REAL*8

The

8
PRECISION

COMPLEX

COMPLEX*8

CHARACTER*1len

len

l-byte

values

storage

true

integers
b:

2
4

INTEGER*2

DOUBLE

the

area

can

false,

range

-128

contain
single

the

1logical

character,

+127.

Either

two or four bytes are allocated depending on
compiler
command
qualifier
specified.
The
default allocation is two bytes.
When
four
bytes
are
allocated,
all
four
bytes
are
used
for
computation.
the

The value
specified;

the

BYTE

and

2.3.1
An

range

LOGICAL*1

Integer

integer

have

integer

1len
this

are

1is
the
number
number can be any

Leading

constant

whole

sign
and
1is
has the form:

optional

sign.

0s,

decimal

point.

Constants

1leading
constant

string

within

synonymous.

number

numeric

any,

are

characters.
ignored.

with

interpreted

characters

integer

255.

snn

decimal

can

number.

STATEMENT

minus

sign

1is

must

appear

optional

assumed

Except

for

the

sign,

other

than

the

numerals

The

absolute

before

COMPONENTS

negative

positive

integer

constant

(an

constant;
unsigned

plus

constant

positive).

value

integer

constant

through

cannot

contain

character

integer

constant

cannot

greater

than

2147483647.

Examples

valid

and

valid

invalid

integer

constants

are:

Invalid
0

99999999999
3.14
32,767

-127
+32123

(too

large)

(decimal point and
comma hot allowed)
-~

the

value

4-byte

2.3.2
A

data

constant
a

within

2-byte

type;

signed

Real

real

one

represents

INTEGER*2

quantity

value

and

range

-32768

quantity
outside

treated

and

this

+32767,

1is

treated

range,

INTEGER*4

this
as

represents

data

type.

Constants

constant

number

with

three

forms:

basic

real

constant

basic

real

constant

basic

the

signed

real

integer

constant

decimal

followed

string

point

decimal

and

can

decimal

digits

occur

any

exponent

one

three

formats:
S.nn
snn.nn

snn.

optional

sign.

A string of decimal digits.
The

decimal

digits

Leading

counting

point

not
(0s
the

can

limited,
to

the

appear

anywhere

but

the

left

leftmost

0.00001234567, all of the
the 0s is significant.

decimal
Esnn

exponent

has

the

only
of
7

the

first

digits;

nonzero

form:

the

leftmost

digits

string.
7

nonzero

are

digit)

therefore,
are

The

digits

are

1in

significant,

number

significant.
ignored

the
but

constant
none

STATEMENT COMPONENTS

optional

integer

sign.

constant.

or
real
The exponent represents a power of 10 by which the preceding
represents
1.0E6
example,
for
multiplied;
be
to
is
constant
integer
the

value

1.0

A real constant occupies four bytes
and
1is
interpreted
as
number with a precision, typically, of seven decimal digits.

real

A minus sign must appear between the letter E and a negative exponent;
a plus sign is optional between the letter E and a positive exponent.

Except for algebraic signs and a decimal point, and the
letter
E
if
used,
a
real
constant
cannot
contain
a
character other than the
numerals

through

If the letter E appears
exponent must follow it.
can

in
a
real
constant,
an
integer
constant
The exponent cannot be omitted;
however, it

The magnitude of a
nonzero
real
approximately 0.29E-38 or greater
Examples

valid

and

invalid

constant
cannot
be
smaller
than approximately 1.7E38.

real

constants

valid

Invalid

3.14159
621712.
-.00127
+5.0E3
2E-3

1,234,567
325E-45
~-47.E47
100
$25.00

2.3.3

than

are:

(commas not allowed)
(too small)
(too large)
(decimal point missing)
(special character
not

allowed)

Double-Precision Constants

A double-precision constant is
constant followed by a decimal

a basic real
constant
exponent of the form:

integer

Dsnn

optional

integer

sign.

constant.

A double-precision constant occupies eight bytes and is interpreted as
a
real number with a precision, typically, of 16 decimal digits.
The
number of digits that precede the exponent is not
1limited,
but
only
the

leftmost

A minus

sign

digits

must

are

appear

significant.

before

negative

double-precision

constant;

a plus sign is optional before a positive constant.
A minus sign must
appear between the letter D and a negative exponent;
a plus
sign
1is
optional between the letter D and a positive exponent.

2-6

STATEMENT

COMPONENTS

The exponent following the letter D cannot be
can

The

magnitude

of a
approximately

than

omitted;

Examples

valid

nonzero

double-precision

0.29D-38
and

invalid

greater

constant

than

however,

cannot

approximately

double-precision

constants

are:

Invalid

1234567890D+5
+2.71828182846182D00

1234567890D45
1234567890.0D~-89

(too
(too

+2.7182812846182

(no Dsnn
this is

large)
small)

real

2.3.4

Complex

complex

comma

and

real

part

the

present;
valid
constant)
a

Constants

constant

enclosed

pair
in

integer

parentheses.

complex

number,

part.

smaller

1.7D38.

valid

-72.5D-15
1DO

real

The

the

constants

first

second

separated

constant

represents

the

imaginary

complex

constant

has

the

form:

(rc,rc)
rc
.

A
The

real

parentheses

required.
A

constant.

See

complex

and

comma

Section

constant

are

2.3.2

part

for

occupies

the

eight

the

rules
bytes

complex

for
and

number.

Examples

valid

and

invalid

complex

constant

forming

constants

(1.70391,-1.70391)

(1.23,)

(second

missing)

real

Octal

Octal
and

numeric

and

Hexadecimal

hexadecimal
constants;

constant

are

not

allowed)

Constants

constants
you

(double-precision

constants

2.3.5

are

are:

Invaliad

(1.0,1.0D0)

and

constants.

interpreted

valiad

(+12739E3,0.)

real

can

are
use

alternative

them

wherever

string

of octal

ways
numeric

represent

constants

are

enclosed

allowed.

An octal

constant
is an unsigned

apostrophes

and

constant

the

has

followed

the

form:

'clc2c3...cn'0

A digit

the

range

alphabetic

digits
character

octal

STATEMENT COMPONENTS

string

A hexadecimal constant is an unsigned

hexadecimal

digits

enclosed by apostrophes and followed by the alphabetic character X.
constant has

hexadecimal

the

form:

'‘clc2c3...cn'X

in the range

A hexadecimal digit in the range 0 to 9, or a letter
F or

A to

Leading

zeros are

£.

Examples of valid

in octal

ignored

specify up to 32 bits

and hexadecimal

invalid octal

and

valid

Invalid

'07737'0
'1'0

'7782'0
7772'0
'0737"

and

constants are:

(invalid character)
(no initial apostrophe)
(no 0 after second apostrophe)
(signed)

'-4367"

Examples of valid

You can

constants.

(11 octal digits, 8 hexadecimal digits).

invalid hexadecimal

constants are:

Invaliad

valid

'AF9730'X
'FFABC'X

'999.,'X

(invalid character)

'FOX

(no apostrophe before

'-ACF4!

(signed)

the

Octal and hexadecimal constants are typeless numeric constants;
they
assume
data
types
that are based on the way they are used (and thus
they are

not converted

before

use),

follows:

When the constant is used with a
binary
operator,
including
the
assignment operator, the data type of the constant is the
data

type of

the other operand.

For

Data

Statement

example:

Type

Length of

of Constant

Constant

REAL*4
INTEGER*2
REAL*8

4
2
8

REAL*8 DOUBLE
INTEGER*4 N

RAPHA = '99AF2'X
JCOUNT = ICOUNT + '777'0
DOUBLE = 'FFF99A'X

IF(N.EQ.'123'0)

GO TO 10

INTEGER*4

When a specific data type —-- generally integer -- is
this type is assumed for the constant. For example:

required,

Statement

Data Type
of Constant

Length of
Constant

Y(IX)=Y('15'0)+3.

INTEGER*2

When the constant is used as an actual argument, no data
is

assumed;

For

example:

however,

length of

two bytes

is always

Statement

Data Type
of Constant

Length of
Constant

CALL APAC('34BC'x)

None

type
used.

STATEMENT

When

the

type

constant

assumed.

For

used

COMPONENTS

any

other

Data
Statement

IF('AF77'X)

An
of

octal or
data.

context,

INTEGER*2

Type

Length

Constant

'7777'0

1,2,3

INTEGER*2

.NOT.'73777'0

INTEGER*2

'A39'X

Constant

data

example:

INTEGER*2

hexadecimal constant actually specifies as much as 4 bytes
When the data type implies that the length of the constant
than the number of digits specified, the leftmost digits
have

a
value
of
zero.
When the data type implies that the length of the
constant is less than the number of digits specified, the constant
is
truncated
on
the
left.
An error results if any nonzero digits are
truncated.
Table 2-2 lists the number of bytes that
each
data
type
requires.

2.3.6

Logical

A logical
following

Constants

constant specifies
true
two logical constants are

or
false;
possible:

therefore,

only

the

.TRUE.

.FALSE.

The

delimiting

2.3.7

periods

are

required

string

part

each

constant.

Character Constants

A character
enclosed by

constant
1is
apostrophes.

constant

character

has

the

printable

ASCII

characters

form:

'clc2c3...Cn’

A
Both

printable

delimiting

character.
apostrophes

must

present.

The value of a character constant is the string of characters
between
the delimiting apostrophes.
The value does not include the delimiting
apostrophes,
but
does
include
all
spaces
or
tabs
within
the
apostrophes.
Within a character constant, the apostrophe character
by
two
consecutive
apostrophes
(with
no
space or
between them).
The

length

the

character

constant

'is

the

number

1is
represented
other character

between
the
delimiting
apostrophes
(two
consecutive
apostrophes counting as one character).
The
1length
of
a
constant must be in the range 1 through 255.

characters

internal
character

STATEMENT COMPONENTS

and

Examples of valid

invalid character constants are:

valid

Invalid

'"WHAT?'

'HEADINGS

(no trailing

apostrophe)

'HE SAID,

(character constant

1S:'

'TODAY''S DATE

contain

one

character)

least

(quotation marks

"NOW OR NEVER"

"HELLO"'

must

cannot be used in
place of apostrophes)

If a character constant appears in a numeric context (for example,
as
the
expression
on
the
right
side
of
an
arithmetic
assignment

statement),

1is

considered

Hollerith

constant

(see

Section

203.8.) [

Hollerith Constants

2.3.8

A Hollerith constant
character

count

A Hollerith

and

is a string of printable characters preceded
the

constant

has

letter
the

by a

form:

nHclc2c3...Cn

An unsigned, nonzero
integer
constant
stating
the
characters in the string (including spaces and tabs).

printable

number

character.

The maximum number

characters

Hollerith constants are

stored

255.

byte

strings,

one

character

per

byte.

Hollerith constants have no data type;
they
assume
a
numeric
data
type
according
to
the
context
in
which they are used.
Hollerith
constants cannot assume a character data type and cannot be used where
a

character

value

Examples of valid

expected.

and

invalid

valid

Hollerith

constants

are:

Invalid

16HTODAY'S DATE

1IS:

3HABCD

(wrong

number

characters)

1HB

When Hollerith constants
a data type according to

are
the

When the constant

used in numeric expressions,
following rules:

is used with a binary

they

operator,

assume

including

the assignment operator, the data type of the constant
data type of the other operand.
For example:

the

STATEMENT

COMPONENTS

Data

Statement

INTEGER*2

REAL*8

)

4HABCD

ICOUNT

DOUBLE

8HABCDEFGH

the

specific

+2HXY

data

constant.

type

For

INTEGER*2

REAL*8

required,

Data
of

X=Y (1HA)

the constant is used
assumed.
For example:

APAC

When

the

data

type

Type

type

(9HABCDEFGHI)

assumed

actual

argument,

Type

Data

context,

Type

Length

Constant

INTEGER*2

Constant

(2HAB)

INTEGER*2

1HC-1HA

INTEGER*2

.NOT.

INTEGER*2

1lHB

type

Constant

1,2,3

data

is used in
any
other
assumed.
For example:

Length

Constant

None

Statement

Constant

constant

Length

Constant

Data
Statement

CALL

this

INTEGER*2

When

REAL*4

example:

Statement

)

ICOUNT

RALPHA

for

Length

Constant

DOUBLE

JCOUNT

When

Type

Constant

When
data

the length of the constant is less than the length implied by the
type, spaces are appended to the constant on the right;
when the
length of the constant is greater than the length implied by the
data

type, the constant is truncated on
nonblank characters are truncated.
Table

2-2

lists

Each

character

2.4

VARIABLES

the

number

occupies

one

the

right.

characters

byte

required

error

for

results

each

data

any

type.

storage.

variable is a symbolic name associated with a storage location
(see
Section
2.1
for
the
form
of
a
symbolic name).
The value of the
variable is the value currently stored in that location;
however, you
can change that value by assigning a new value to the variable.

constants,

variables are classified by data type.
The data
type
indicates the type of data the variable represents, its
its storage requirements.
When data
of
any
type
is
a variable, this data is converted, if necessary, to the
the variable.
You can
establish
the
data
type
of
a
using type declaration statements or IMPLICIT statements,

of
a variable
precision, and

assigned
data type

of
variable
by
or by choosing names
any other for real).

that

begin

with

certain

letters

(I-N

for

integer;

STATEMENT COMPONENTS

Two or more variables are associated with each other when
they
refer
to
the same memory location.
They are partially assocliated when part
of the location to which one variable refers is the same
as
part
or
all
of
the location to which the other variable refers.
Association
and

partial

association

EQUIVALENCE

statements,

occur

when

you

use

COMMON

and actual and dummy arguments

statements,

in subprogram

references,

A variable is considered defined if the
storage
location
associated
with
it
contains
data
of
the
same
type as the variable name.
A
variable can be defined before program execution by a DATA
statement,
or during execution by an assignment or input statement.

If variables of different data
types
are
associated
(or
partially
associated)
with
the
same storage location, and if the value of one
variable is defined (for example, by assignment),
the
wvalue
of
the
other
variable
becomes
undefined;
that
1is,
1its
wvalue cannot be
predicted.

2.4.1
To

Data Typing by Specification

specify the data

statements

(see

types

Section

COMPLEX VAR1
DOUBLE PRECISION

5.2).

variables,
For

example,

you

the

use

type

statements

declaration

VAR2

assign the COMPLEX data type to
the
wvariable
VARl
and
the
DOUBLE
PRECISION
data
type
to
the variable VAR2:
that is, they cause the
variable VARl to be associated with an 8-byte
storage
1location
that
will contain complex data, and the variable VAR2 to be associated with
an 8-byte double-precision storage location.
Character type declaration
and
a
value
length to

statements
specified

assign the character
data
variables.
For
example,

type
the

statements

CHARACTER*72

INLINE

CHARACTER NAME*12,

NUMBER*9

cause the variables INLINE, NAME, and NUMBER
to
be
associated
with
storage
locations containing character data of lengths 72, 12, and 9,
respectively.

The IMPLICIT statement (see Section 5.1) has a
more
general
effect:
it
assigns,
in
the
absence
of
an
explicit
type
declaration, a
specified data type to any variable beginning with a specified
letter
or any letter within a specified range.

You can explicitly declare the data
explicit declaration

2.4.2

takes

type of a variable only once.

precedence

over

IMPLICIT statement.

Data Typing by Implication

In the absence of
either
IMPLICIT
statements
or
type
declaration
statements, all variables you use that have names beginning with I, J,
K, L, M, or N are assumed to be integer variables, and those that have
names
beginning
with
any
other
letter
are
assumed
to
be
real
variables.

For

example:

STATEMENT

Real

2.5

COMPONENTS

Variables

Integer

Variables

ALPHA

JCOUNT

BETA

ITEM

TOTAL

NTOTAL

ARRAYS

array

single

locations,
appended
In

PDP-11

single

the

column

refer

row

number

several

this

The

and

its
1is

following

page

The

DIMENSION

The

COMMON

The

VIRTUAL

statements

the

have

discusses

from

example,

associated

one

with

individual

referred
2.5.2

storage
subscript

subscripts.)

seven

array

dimensions.

having

only

one

array;
to refer to a value in
this
the value's row number.
Similarly a
figures

array,

number.

And

the

you

two-dimensional

must

three-dimensional

specify

table

array;

value's

statements

statement

(see
(see

contain

array

name

number

the

(see

statement

may

the

this

FORTRAN-77

define

can

for

column

declaration

that

are

The

figures

row

both

refer

array;

the

value's

that
to

number,

covers
value

its

column

number.

PDP-11

These

array

locations

name).

(Section

specify

Type

and

column

array,

elements,

name.

one

you must
its

storage

array

figures,

value

pages

and

(the

one-dimensional
only
specify

than

array,

number,

or a
need

contiguous

array

FORTRAN-77,

dimension -array,
Yyou
of

name

called

table

group

symbolic

Section

Section
Section

the

each

arrays:

5.2)

5.3)

5.4)
5.5)

declarators

array,

elements

establish

number

(see

Section

dimensions

2.5.1)

the

dimension.

element of an array is considered defined if the
storage
1location
associated
with
it
contains data of the same type as the array name
(see Section 2.5.4).
An array element
or
an
entire
array
can
be
defined
before
program
execution
by
a
DATA
statement.
An array
element can be defined during program execution by
an
assignment
or

input
statement;
an
entire
array
execution by an input statement.

2,5.1
An

Array

array

specifies

program

unit,

the

and

array.

defined

during

that

program

symbolic

name

specifies

the

identify

properties

of
'

array

Declarators

declarator

within

can

declarator

(d[,d]

...)

has

the

form:

this

STATEMENT COMPONENTS

array

the
1is,
that
-array
The symbolic name of the
(Section 2.1 gives the form of a symbolic name.)

name.

A dimension declarator.

The number of dimension declarators indicates the number of dimensions
the number of dimensions can range from one to seven.

in the array;

For

example,

DIMENSION

IUNIT

(10,10,10)

three-dimensional

IUNIT is a

array.

The value of a dimension declarator specifies the number of elements
in the example above, each dimension of IUNIT
that dimension:
in
consists

elements.

to the product of the
The number of elements in an array is equal
IUNIT above contains 1000
values of the dimension declarators;
elements

(10

10).

An array name can appear in only one array declarator within a program
unit.

Dimension declarators that vary in value are not permitted in a main
but they are permitted in a subprogram in order to define
program,
single
a
within
arrays
adjustable
You can use
adjustable arrays.
subprogram--to process arrays with different dimension declarators--by
specifying
arguments.

array name
the declarators as well as the
(See Section 6.1.2 for more information.)

A dimension declarator in PDP-11 FORTRAN-77 can specify both
an

and

bound

[dl:]

upper

bound,

subprogram
a

lower

(*);

see

and

1lower

follows:

The

lower

bound

the dimension.

The

upper bound of

the dimension.

(Can be an asterisk

below.)

The number of elements specified by a dimension with upper
bounds

is du-dl+1l.

range of
a
Specifying the lower bound of an array allows you to use
For example, to reference an
does not begin with 1.
that
subscripts
an
specify
could
array storing data for the years 1964 to 1974, you
upper bound of 74 and a
DIMENSION

KYEAR

lower bound of 64 as

follows:

(64:74)

The value of the lower bound, dl, can be
negative,
0,
or
positive.
The value of the upper bound, du, must be greater than or equal to the

|is
it
If a lower bound is not specified,
corresponding lower bound.
1is 1 and that the value of the upper
bound
1lower
the
that
assumed
bound

the number

of elements

the dimension.

STATEMENT

For

example,

DIMENSION

NUM

contains

The

upper

the
NUM

statement
(0:9,-1:1)

elements.

bound

the

dimension

declarators

declarator

Each

dimension
e

Each

COMPONENTS

last

may

assumed-size

bound

dimension

declarator

asterisk;

array

declarator

(see

integer

arithmetic

1list

asterisk

1in

marks

the

Section

6.1.3).

expression

which:

operand
1is
an
integer
constant,
an
integer
or an integer variable in a COMMON block

dummy

argument,

e
Array

Each

operator

references

and

bounds

expressions.

2.5.2

Subscripts

subscript

function

list

references

expressions,

operator

are

not

called

allowed

subscript

expressions,

enclosed
1in
parentheses,
that
specify,
or reference,
element in an array;
a subscript is said to "qualify" an
A subscript is appended to the array name it qualifies.
A

subscript

has

the

dimension

a particular
array
name.

form:

(sl,s]...)

A
A

subscript

expression.

expression

expression.

converted

integer

subscripted

the

array

for

each

dimension

2.5.3

Array

Storage

suggested

earlier

dimension

can

value
by

be
of

a
a

constant,
subscript

truncating

reference

must

defined

for

any

a
is

fractional

contain
the

variable,
not

array

one

type

arithmetic

integer,

part.
subscript

expression

being

referenced

think

(one

for

declarator).

Section

2.5,

you

can

array

arrangement
of values in rows, columns, and pages (or planes) -- that
is, as an arrangment
of
wvalues
in
other
than
a
strictly
1linear
sequence,
An
array of any size is always stored in memory, however,
as a linear sequence of values:
A
one-dimensional
array
1is
stored
with
1its
first
element
1in the first storage location, and its last
element
1in
the
1last
storage
location
of
the
sequence;
a
multidimensional
array is stored so that the leftmost subscripts vary
most rapidly.
This storage
arrangement
for
arrays
1is
called
the
"order
of
subscript
progression." Figure 2-1 shows array storage in
one, two, and three dimensions.

STATEMENT

One-Dimensional

Array

COMPONENTS

BRC(6)

LIIBRC(I) 2|BRC(2)]3|BRC(3) 4lBRC(4)[SIBRC(S)IGIBRC(G)]
A

)

Memory

W N =

Two-Dimensional

Array

Positions

BAN(3,4)

BAN(1,1)|4|BAN(1,2)|7|BAN(1,3)|10}{BAN(1,4)

BAN(2,1)

|{S|BAN(2,2)

BAN(3,1)

|BAN(2,3)|11|BAN(2,4)

|[BAN(3,2)|9

Memory

Three-Dimensional

Array

[BAN(3,3)

|12

|{BAN(3,4)

Positions

BO0S(3,3,3)

19{B0OS(1,1,3)]|22|B0S(1,2,3) [25|B0S(1,3,3)}

20]B0OS(2,1,3)[23|B0S(2,2,3) [26]/B0s(2,3,3)1}
10/BOS(1,1,2)]|13|B0OS(1,2,2)]16|B0S(1,3,2)§27[B0S(3,3,3)1

18 |B0S(3,3,2)}

L
o

=31
LY N[+

11/B0S(2,1,2)[14]B0S(2,2,2)[17[B0S(2,3,2)]

BOS(1,1,1)]4[B0S(1,2,1)[7[B0S(1,3,1)}
BOS (2,1,1)

5 BOS(2,2,1) 8 BOS(2,3,1)]
Bos(3,1,1)[6[BOS(3,2,1){9]BOS(3,3,1)]
Memory

Figure

2.5.4

Data Type of

Positions

2-1:

Array

Storage

an Array

The data type of an array is specified in the same way that
the
data
type
of any other variable is specified -- that is, implicitly by the
initial letter of the
name,
or
explicitly
by
a
type
declaration
statement.

All the values in an
array
have
the
same
data
type.
Any
value
assigned
to
an
array
element
1is converted to the data type of the
array.
1If an array is named in
a
DOUBLE
PRECISION
statement,
for
example,

the

compiler

element

the

element

this

2.5.5

array.

array,

allocates
When

value

Type

declaration

COMMON

DATA

statement

converted

Array References Without

In the following types of
array
1is
to be used (or
without its subscript:

8-byte
any

storage

type

double

1is

location

for

each

assigned

any

precision.

Subscripts

statements, you can indicate that .an
entire
defined) simply by specifying the array name

statements

STATEMENT

EQUIVALENCE

FUNCTION

SUBROUTINE

Input/output

ENTRY

SAVE

COMPONENTS

statement

statement
statement

statements

statement
statement

You

can also use unsubscripted array
references
to external procedures.

permitted

2.5.6

any

other

type

names
as
actual
Unsubscripted array

Adjustable Arrays

dimensions.
To
the array bounds

Chapter

wuse an
and the

for more

CHARACTER

adjustable
array name

character

variable

array in a subprogram, you specify
as
subprogram
arguments.
(See

information.)

SUBSTRINGS

A character substring is a contiguous
or character array element.
A

1in
not

statement.

Adjustable arrays allow subprograms to manipulate arrays

2.6

arguments
names are

substring

reference

has

segment

one

the

character

variable

forms:

v([el]l:[e2])

a(sf,sl...)

([el]l:[e2])

character

variable

character

array

subscript

expression.

name.

A
numeric
position of

expression
that
a substring.

specifies

the

1leftmost

character

rightmost

character

numeric
expression
that
position of a substring.

specifies

the

Character positions within a character variable or array
element
are
numbered
from
1left
to
right, beginning with 1.
For example, LABEL
(2:7) specifies the substring
beginning
with
the
second
character
position and
ending
with
the
seventh
character
position
of the

STATEMENT COMPONENTS

character variable LABEL.
If the CHARACTER*8
variable
LABEL
has
a
has a value of
LABEL(2:7)
substring
the
then
XVERSUSY,
of
value
VERSUS.

If the value of the numeric
expression
el
or
e2
1is
not
of
type
integer,
it is converted to an integer value before use by truncating
any

fractional

The values of
following

part.

the

numeric

expressions

and

must

meet

the

conditions:

.LE.

The

length of

len

.LE.

1
len

If el

is omitted,

omitted,

the character variable or

FORTRAN-77 assumes that

FORTRAN-77

assumes

that

equals

array element.

len.

-equals

For example, NAMES(1,3)(:7) specifies the substring
first
character
position
and
ending
with
the
position of the character array element NAMES(1,3).

2.7

starting
seventh

with
the
character

EXPRESSIONS

An expression consists of a

single basic

component

(such as a constant

or
a
variable) or a combination of basic components with one or more
operators
that
represents
a
single
value,
Operators
specify
computations to be performed on the values of the basic components.
Expressions are classified as arithmetic,
character,
relational,
or
logical.
Arithmetic
expressions
produce
numeric values, character
expressions produce
character
values,
and
relational
and
logical
expressions

produce

logical

values.

Arithmetic Expressions

2.7.1

Arithmetic expressions are expressions that are formed with arithmetic
elements
and
arithmetic
operators.
The evaluation of an arithmetic
expression yields a single numeric value.
An

arithmetic

element can be

any of

)

A numeric,

)

A numeric

variable

array

)

arithmetic

expression

arithmetic

function

numeric

Hollerith,

octal,

following:

hexadecimal

constant

element

The term "numeric," as used
logical
data
1is
treated
context.

the

enclosed

parentheses

reference

above,
includes
1logical
data,
because
as integer data when used in an arithmetic

STATEMENT

Arithmetic
the

operators

values

result.,

The

specify

arithmetic

operators

and

Operator

These
two

COMPONENTS

computation

elements
their

meanings

that is to be performed
on
produce a numeric value as a
are:

Function

* %

Exponentiation

Multiplication

Division

Addition

Subtraction

operators

are

elements,

called

When

and

binary

written

unary

and

plus

unary

operators

can

except

use

A variable
used in an
Table
types,

2-3
and

any

noted

arithmetic

Table

operator

with

the

also

each

preceding

wvalue,

any

the

valid

is
an

used

with

arithmetic

plus

(+)

arithmetic

and

element,

2-3.

or array element must have
arithmetic expression.
shows

because

immediately

element, to denote a positive or negative
minus (-) symbols are unary operators.,
You

minus

allowed

shows

the

Table

2-3:

defined

combinations

data

type

the

base
result

Exponentiation

Exponent

value

Data

before

and
of

can

exponent

data

exponentiation.

Types

Type

Base

Type

Integer

Real

Double

Complex

Integer

Real

Double

Complex

Real

Double

Complex

Double

Complex

be
an

exponentiated
element with a

Note:

only

negative

element

integer

0 value cannot
element.

element;

can
and

exponentiated

In any valid exponentiation,
base
element,
except
in

the result has
two
cases:

another

the
(1)

0-value

same data
a
real

type
base

as
the
and
a

double-precision exponent produces a double-precision result;
and
(2)
a base of any type and a complex exponent produces a complex result.

Arithmetic

expressions

are

the
operators
involved.
in the following order of

evaluated

order

The five operators
precedence:

that

FORTRAN

determined
are

performed

STATEMENT

COMPONENTS

Operator

Precedence

* %

First

“*

and

Second

and

Third

When two or more operators of equal
precedence
(such
as
+
and
-)
appear,
they
are
evaluated
by
the
compiler
in any order that is
algebraically equivalent to a left-to-right order of evaluation.
For
example,
in
3+4-1, the addition is performed before the subtraction.
Exponentiation, however, is evaluated right to left.
For example,
1in
the
expression A**B**C, B**C is evaluated first, and then A is raised
to

the

result

2.7.1.1

Use of

B**(C.

Parentheses -

You

can

use

parentheses

force

particular
order
of
evaluation.
When
part
of
an
expression is
enclosed in parentheses, this part is evaluated first,
and
then
the
result
is
wused in the evaluation of the remainder of the expression.
In the following examples, the numbers below
the
operators
indicate
the order of evaluation:

4+3*%2-6/2=7

(443)

(4+3*2-6)/2=2

((4+3)*2—6)12=4
1

shown

the

third

and

fourth

examples

parentheses are evaluated according to
unless you override the order by using

above,

expressions

within

the normal order of precedence,
parentheses within parentheses.

Using parentheses to specify evaluation order is
often
important
high-accuracy
computations
because
rounding
and normalizations
cause
algebraically
equivalent
evaluation
orders
not
to
computationally equivalent.
Using parentheses to specify
complex
expressions,
where
writing a program to analyze
you

have

any

doubt

about

evaluation order
1is
also
it
is
difficult
during
visually what is to happen

accuracy,

use

important
the process
to
what.

in
may
be

in
of
If

parentheses.

2,7.1.2
Data Type of an Arithmetic Expression - If every
element
in
an
arithmetic expression is of the same data type, the value produced
by the expression is also of this data type.
If elements of different
data
types are combined in an expression, the data type of the result
of each operation is determined by a rank associated
with
each
data
type.
The data types are ranked as follows:

STATEMENT

Data

Type

Rank

Logicai

1l (Low)

Integer

Real

Double

Precision

Complex
The

data

type

elements

the

value

element

resulting

last

data

from
type

operation

Operations
)

are

the

expression

classified

operation
1is

the

operation.
an

types

performed

that

integer
the

For
and

data

that

rounded.

1/3

The

value

PDP-11

element

For

1/3
of

element

the

Real

type

results

this

type

equal

division

performed
only
in an arithmetic
arithmetic,
any

1is

truncated,

and
Real

integer
giving

The

not

operations
of

1is

are

present

integer
1is

INTEGER%*2

out

operations

double-precision

precision, by making the
significant portion of a
significant
then

portion

evaluated

Converting a
not increase

Any

operation

given

the

only

and

logical

are

converted
a

real
part

evaluated

wusing

converted

integer

element
element;
The

real

(I/J)*X
J,
and
and X.

element
to

(approximately):

0.3333333134651184D0

double

the
the

most
least

expression

Iis

arithmetic.

real element to a double-precision element
its accuracy.
For example, the real number

0.3333333
is

real

fractional

value

integer,

real or
integer
double-precision

double-precision

result.

performed

element

then

carried

INTEGER*4

real,

elements
each

expression

Double-precision
a

not

involving

element

produces

combinations
by

arithmetic.
Note, however, that in the statement Y =
an integer division operation is performed on I
and
then a real multiplication is performed on the result
)

the

follows:

operation

INTEGER*4

Any
0.

from

expression

operations

elements.,

real.

1/3

operation

data

result

the

wvalue

expression.

data

FORTRAN-77,

elements

the

example:

and

INTEGER*4

arithmetic

type

example,
real

type

two

data

Integer operations —-- Integer operations are
on integer elements.
(Logical entities used
context are treated as integers.)
In integer

fraction

data

operation
an

(High)

produced

different

highest-ranked

The

COMPONENTS

does

STATEMENT COMPONENTS

not

either:

0.3333333000000000D0
or:

0.3333333333333333D0

)

expression
operations -- In an operation on an
Complex
a complex element, integer elements are converted
containing
and
described,
previously
as
type,
data
real
to
double-precision elements are converted to real data type, by
element
real
The
rounding the least-significant portion.
1is designated as the real part of a complex number;
obtained
Iis
The expression
the imaginary part is given the value 0.
then evaluated with complex arithmetic, and the resulting
value

complex.

Character Expressions

2.7.2

The evaluation
Character expressions consist of character elements.
of a character expression yields a single value of character data
type.

A character element can be any one of the following:
e

A character

constant

A character

variable

A character

array element

A character

substring

expression has

A character

character

and

can be

enclosed

A
relational
by
separated
true

element

Relational

2.7.3

the

form:

the

with

parentheses.

Expressions

expression
consists
of
two
arithmetic
expressions
The value of the expression is
relational operator.
a

stated

relationship exists,

false

it does not.

A relational operator tests for a relationship between two
expressions.

These

operators

are:

Relationship

Operator

than

.LT.

~Less

.LE.

Less than or equal

.EQ.

Equal

.NE.

Not equal

.GT.

Greater

than

.GE,

Greater

than or equal

2-22

arithmetic

STATEMENT

The

delimiting

Complex

periods

expressions

can

operators.
Complex
imaginary parts are
In

arithmetic

example,

required

entities are
both equal.

relational

evaluated
and
then
to determine whether
For

are

the

the
the

COMPONENTS

part

only

equal

expression,

each
by

their

the

operator.

the

.EQ.

and

corresponding

arithmetic

.NE.

real

and

expressions

are

resulting values are compared with each other
relationship stated by the - operator
exists.

expression

APPLE+PEACH

.GT.

PEAR+ORANGE

states

the relationship:
"The sum of the
real
variables
APPLE
and
PEACH
1is greater than the sum of the real variables PEAR and ORANGE."
if this relationship exists, the value of the expression is true;
if

not,

the

character

value

evaluated

the

then

whether

FORTRAN-77

character
means

"follows

false,

expression,
resulting

the

relationship

1In
1in

the
uses

values.,

"precedes

means

expression

relational

and

determine

PDP-11

the

ASCII

character
are

stated

ASCII

character
the

the

values

the

<collating

relational
collating

collating

expressions

compared

with

each

operator

sequence

expressions,

sequence,"

and

sequence."TM

are
other

exists;
comparing

"less

than"

"greater

than"

For

example,

the

expression
'ABZZZ'
states

that

.LT.

'cCcccc'!

'ABZZZ'

less

does
exist, the value of
stated did not exist, the
If

the

two

character

same

1length,

spaces until
expressions
'ABC'
'AB!
the

first

though

'AB'

shorter

lengths

L.EQ.

'ABC

has

expressions

Because

are

in
of

relational

the

equal.

two

For

this

relationship

If the relationship
would be false.
expression

padded

example,

the

are

not

right

with

relational

'C
a

value

are

not

'CCCCC'.

expressions
the

the

than

the expression is true.
value of the expression

longer

true,

-equal;
than

even

and

the

though
second

the

has

1lengths
value

the

true

even

'C'.

All

relational operators
have
arithmetic
operators
have
a

the
same
precedence;
higher
precedence than

however,
the
the relational

operators.

You

can

use

parentheses

alter

the

order

expressions
1in
a relational expression;
operators are evaluated before
relational
enclose

the

whole

arithmetic

however, because
operators,
you

arithmetic
need. not

expression

evaluation

parentheses.

You can compare two numeric expressions of different data types
in
a
relational expression.
To make such a comparison, the system converts
the value of the expression with the lower-ranked
data
type
to
the
data

type

the

expression

with

the

higher-ranked

data

type.

STATEMENT COMPONENTS

Logical Expressions

2.7.4

Logical expressions are
logical
A
operators.
either

true

A logical

The

the

following:

)

integer or

logical

constant

integer or

logical

variable

integer or

logical

array

)

A relational

)

A logical

expression

operators

Operator

element

expression enclosed

integer

logical

function

parentheses

reference

are:
Meaning

Example

The expression is
Logical conjunction:
if, and only if, both A and B are
true

.AND.

+AND.

logical
value--

false.

element can be any of

logical

elements
and
single logical

formed
with
logical
a
yields
expression

true.

The
B,

.XOR.

«XOR.

(inclusive
disjunction
is true if either
both, is true.

Logical

.OR.

expression
or

The
expression
exclusive OR:
if A is true and B is false, or

Logical
is true

OR)
:
A or

vice

versa;

false

1if

both

the
expression
is
but
elements have the same

value.
.NEQV.

.EQV.

.NEQV.
B

Same

Logical

.XOR.

equivalence:

The

expression

true if, and only if, both A and B have
the same logical value, whether true or
false.

NOT.

. NOT.

Logical negation:
true if, and only

The delimiting periods of logical operators are

The
if, A

expression
is false.

1is

required.

A logical expression is evaluated in accordance with the precedence of
The following list
the arithmetic, relational, and logical operators.
a
logical
expression
are
gives the order in which the operators in
evaluated:
Operator

Precedence
First

* %

and

Second

and

Third

(Highest)

STATEMENT

Operator
'"The

Precedence

relational

operators

Fourth

«NOT.

Fifth

«AND.,

Sixth

.OR.

Seventh

.XOR., .EQV., .NEQV.
Operators

example,

equal

the

A*B+C*ABC
the

COMPONENTS

sequence

Eighth

rank

are

evaluated

from

1left

right.

For

expression
.EQ.

X*Y+DM/ZZ

which

.AND.

evaluation

.NOT.

occurs

K*B

.GT.

is:

(((A*B)+ (C*ABC)) .EQ. ((X*Y)+(DM/ZZ) )} .AND.( .NOT. ((K*B) .GT.TT))

arithmetic

normal

Two

sequence

consecutive

expressions,
of

you

can

use

operators

are

not

parentheses

alter

the

evaluation.,

logical

allowed

unless

the

second

.NOT.

Some logical expressions are
are evaluated.
For example,
A

.AND.

(F(X,Y)

.GT.

evaluated before
if A is .FALSE.
2.0)

.AND.

all their subexpressions
1in the expression

the value of the expression can be determined
by
testing
A
without
evaluating F(X,Y);
therefore, the function subprogram F is not called
and consequences resulting from a call, such as changing variables
1in
COMMON,

When

data

not

occur.

logical
type

elements,

operator

1is

example,

the

INTEGER

I
J
K
J

logical

When

has

operation

on
a

logical

elements,

operator

1is

carried

the

value

out

the

operates

resulting
on

sequence
K

="'65'0
= I.OR.'100'0
= I.AND.'23'0
the

value

'165'0

and

has

'21'0.

bit-by-bit

integer

the
corresponding
bits
of
the
internal
(binary) representation of the
integer elements;
the resulting data type is integer.
When a logical
operator
combines
integer
and
1logical values, the logical value is
first converted to an integer value and then the operation is
carried
out
as
it would be for any two integer elements;
the resulting data
type is integer.
'

For

the

operates

logical.

CHAPTER
3

ASSIGNMENT

Assignment
array

statements

element,

statements

evaluate

specified

variable,

The

four

kinds

Arithmetic

Logical

Character

assign

a
an

STATEMENTS

value

character
expression

array

and

element,

assignment

(or

"define")

substring;

assign

that

the

character

statements

variable,

1is,

assignment

resulting

value

substring.

are:

ASSIGN

3.1
An

ARITHMETIC ASSIGNMENT STATEMENT
arithmetic

variable
The

assignment

array

arithmetic
v

numeric

The

statement

assigns

arithmetic

value

element.

assignment

statement

has

the

form:

variable

arithmetic

equal

rather,

sign
it

array

element.

expression.

does

not

means

"is

mean

"is

replaced

equal
by."

to,"

For

1in

example,

mathematics;
the

assignment

statement

KOUNT

means
the

KOUNT

"Replace

sum of

Although

the

undefined,
references

the

current

symbolic

value

value
name

the

KOUNT

the

integer

and

1left

the
of

wvariable

integer
the

equal

values
must have been previously assigned
in the expression to the right of the equal

KOUNT

constant
sign

to all
sign.

with

1."
can

symbolic

ASSIGNMENT

The

expression must

real

the

expression

entity
and

the

of
is

directly
e
converted to

have

summarizes

the

A character

yield

that

left

the

value

produces

same

STATEMENTS

the

value

proper

greater

the

equal

sign

data

types,

the

For

32767

example,

invalid

INTEGER*2 variable.

statement

the

assigns

value

data types are different, the value
Table
of v before it is assigned.
conversion rules for assignment statements.

of e

to v.
If the
the data type

data

element cannot be

Table

3-1:

assigned

Conversion Rules

numeric

Integer or
Logical

Real

Statements

(E)

Double

Complex

Precision

Element

3-1

entity.

for Assignment

Expression

Variable
or Array

size.

than

(V)
Truncate

Integer

Truncate E to
integer and

Assign E to V

assign to V

Logical

Real

Append

fraction

Append

fraction

(.0) to E and
assign to V

Double
Precision

(.0) to E and
assign to MS

Assign E to Msl
portion of V;

LSl portion of
Vis 0

V is 0

portion of V;

LSl portion of

(.0)

assign

E and

to real

part of V;

imaginary part

0.0

MS = most significant

assign to V

Assign

real

part of V;

of V

imaginary part
0.0

(high order);

real

assign to V;

imaginary part

of E

is not used

Assign msl

Assign real

portion of E to

part of

v; LSl portion
of E is rounded

Assign E to V

portion of

E to V;

imaginary part
of E is not used

Assign

Assign Ms 1

E to

integer and

real

part of E to
Msl portion of

Vv; LSl portion

of V is 0,
imaginary part
of

Append fraction
Complex

Assign E to V

Truncate E to
integer and

part

not

used

real

part of

E is

rounded;

v; Lsl portion

Assign E to V

imaginary part
of V is 0.0

least significant

(low order).

ASSIGNMENT

Examples

valid

and

invalid

STATEMENTS

assignment

statements

are:

Valid
BETA

3.14159

-1./(2.*X)+A*A/(4.%
(X*X))

SUM
= SUM+1.

Invalid
3.14

A-B

(entity

variable
-J

I%*%4

(entity
or

ALPHA

((X+6)*B*B/(X-Y)

the
or

array

(entity

the

3.2
The

LOGICAL ASSIGNMENT
logical

false)

The

logical

assignment
variable

assignment

left

must

variable

the

right

because

the

invalid

parentheses

statement
array

assigns

logical

value

(true

has

the

form:

logical

variable

logical

expression.

logical

data

array

type

element.

and

must

yield

logical

otherwise,
conversions
will
be
made according
resultant values will not be meaningful.

Values, either numeric or
to all variables or array

previously

logical

logical,
elements

assignment

must have
in e,

statements

been

Table

3-1

wvalue;

and

LOGICAL

PAGEND

PAGEND,

PRNTOK

PRNTOK,

are:

ABIG

,FALSE.
LINE

.LE.

.GT.

132

.AND.

.GT.

.NOT.

PAGEND

.AND.

.GT.

Invalid
X=.TRUE.

(entity

the

left

must

the

assigned

Valid

ABIG

element.

statement

Examples

are

balanced)

STATEMENT

must

element)

expression
not

left

array

logical)

ASSIGNMENT

STATEMENTS

CHARACTER ASSIGNMENT STATEMENT

3.3
The

character

assignment

statement assigns

the

value

The

character

assignment

statement has

form:

character

expression to a character variable, array element, or substring.
the

= e
v

A character variable,

character

array element,

expression.

the length of the character

the character variable,

expression

or substring.

truncated

expression

is greater than

the

1length

array element, or substring, the character

the

right.

If the length of the character expression is less than the

the
character
variable,
array
element, or substring,
expression is filled on the right with spaces.
The expression must be of character data

type:

you

length

the character

cannot

assign

numeric value to a character variable, array element, or substring.
Note

that assigning

character
included

substring
if

the

positions
the

a value

substring.

character

wvariables

character

substring

1If

character

position

the

position

data

and

does

character variable or

has a value previously assigned,

Examples of valid and
(All

1in

undefined,

not

outside

these

the

examples

and

undefined.

invalid character assignment statements

arrays

affect

array element not

it remains unchanged;

remains

are

assumed

follow.

type.)

valid
FILE

'PROG2'

'MARCIA'

REVOL (1)
LOCA(3:8)

TEXT(I,J+1)

'PLANTS'

(2:N-1)

'NAMEX'

Invalid

'"ABC'

CHARS =

CHARS

(element on the
array element,

(ixprission on
ype

left must be
or substring

the

right must

a character
reference)

variable,

of character

data

ASSIGNMENT STATEMENTS

ASSIGN
3.4

ASSIGNING

The

ASSIGN

STATEMENT

statement

variable.

The

destination

LABELS

assigns

variable
a

statement

can

subsequent

label

then

wused

assigned

value

integer

specify

transfer

(see

Section

statement

4.1.3).

The

ASSIGN

statement

ASSIGN

label

same

the

form:

program

integer

has

executable
unit

statement

the

ASSIGN

FORMAT

becomes
defined
for use as
as a variable;
that is, the

for

output

The

statement

statement
The

ASSIGN

statement
are

arithmetic

computations.

label

refer

the

must

same

statement
or

executed.

must

occur

For

example,
ASSIGN

program
must

the

ASSIGN

same

variable.

The

assignment statement in
differs
in
that
the

a statement-label reference and
assigned value cannot
be
used

executable

executed

statement

the

undefined

The

the

statement

FORMAT

which

program

the

before
assigned

and

the

assigned

variable

assigned

is
TO

TO
used

statements

unit.

statement
TO

NUMBER

wvariable

arithmetic
operations
the variable NUMBER in
NUMBER

the

unit.

statements

100

associates

variable.

The ASSIGN statement assigns a statement label
ASSIGN
statement
1is similar to an arithmetic
that it assigns a value
to
a
variable, but
variable
undefined

statement

statement.

NUMBER

on
the

with

the variable
statement

the
are

statement
now

invalid.

101

label
For

100;

example,

NUMBER+1

and

does

not

result

value

being

stored

NUMBER.

associated

statement.
assignment

variable

can

become

defined

For
example, assigning
statement as follows:

again

NUMBER

with

value

with

assignment

arithmetic

NUMBER=10

dissociates

the

variable

arithmetic
wvalue
statement, but can

10
be

from

and
used

statement

100.

can no longer
for output and

The

variable

be used in
arithmetic

now has

the

an assigned GO TO
computations.

ASSIGNMENT STATEMENTS
Examples:
valid

Invalid

ASSIGN

TO NSTART

ASSIGN

99999

KSTOP

ASSIGN

250

TO ERROR

(variable must

integer)

CHAPTER 4
CONTROL

Statements

are

written.

However,

normally

to another point
unit.
You
can

STATEMENTS

exected

you

within

may

use

the

same

the

control

order

program

unit

processing,

also
suspension

use
control
statements
of program execution, and

The

statements

are

control
GO

transfers

statement

conditionally

THEN,

executes

ELSE

conditionally
DO

statement

group

CONTINUE

they

are

transfer

control

another

program

to
govern iterative
program termination.

control

within

program

transfers

unit

control

statements

statement

THEN,

execute

which

follows:

statement

conditionally
IF

statements

ELSE,

blocks

specifies

and

END

statements

iterative

processing

statements

specified

number

statement

transfers

control

specified

executable

times.

the

statement

CALL

statement

transfers

RETURN

statement

calling

program

unit

PAUSE

STOP
END

The

statement

statement
statement

foll owing

sections

-~--

returns

control

from

temporarily

terminates
marks

describe

the

program

end

these

suspends

subprogram
a

subprogram

program

execution
program

statements.

unit

execution

the

CONTROL STATEMENTS

GO TO

4.1

GO TO STATEMENTS

TO statements
containing
the

transfer control
GO TO statement.

a
The

point

within

three

types

the
program
unit
of GO TO statements

are:

Unconditional

Computed

Assigned

4.1.1
The

Unconditional

unconditional

statement
The

every

time

unconditional
GO

GO TO Statement

statement

transfers

control

¢to

the

same

executed.
has

the

form:

statement

The

statement

same

program

label.

identified
unit

the

must

GO TO

executable

statement

1in

the

statement.

Examples:

7734

99999

4.1.2
The

Computed
computed

specified
The

computed
GO TO

GO
GO

the
GO

TO Statement
TO

statement

value
TO

statement

(slist)[,]

transfers

arithmetic
has

the

control

statement

expression.

form:

slist
A

list,

called

executable

arithmetic

where

the

transfer

statements,

1list,

separated

expression

the number of

whose

one

the

range

1labels

by commas.

value

statement

labels

the

transfer

list.

CONTROL STATEMENTS
The

computed

the

result

statement

the

label

value

the

TO statement evaluates
integer
data
type.
in

transfer

statement

after

position

less

list,

the

than

control

computed

the

and, if
Control

transfer

greater

necessary,
converts
1is transferred to the

list.

than

transferred

the

number

the

first

labels

executable

TO.

Examples:

(12,24,36),INDEX

(320,330,340,350,360),

the

first

transferred

has

The

assigned
has

Therefore,
executed

the

assigned
GO TO

INDEX
24.

execution

GO TO

GO TO
been

ASSIGN

statement

Assigned

label

The

value

4.1.3

example,

SITU(J,K)+1

has
a
value
of
2,
In the second example,

transferred

statement

340.

Statement

statement transfers control
placed
in
a
variable
by

transfer destination
statement.

execution
is
if SITU(J,K)+1

statement

may depend

has

the

labels

to
an

the

statement
whose
ASSIGN
statement.
most

recently

form:

v[[,](slist)]

integer

variable.

slist
A

list

by
The

one

assigned

statement

transfers

label
on the

was most recently assigned
ASSIGN statement.)

The

statement,

the

and
the statements to
statements in the same

value

PDP-11

slist

must

Examples

(if

ASSIGN

GO TO
(This
ASSIGN
TO

(This

slist

statement
assigned
200

IGO
example
450
IBEG,

associated

the

statements

separated

GO TO

ASSIGN

statement

(See

Section

whose

statements,

3.4

be executable
the
assigned

the

label

value

equivalent

transferred

assigned

statements

equivalent

control

are:

200.)

GO TO

450.)

IBEG

statement

(300,450,1000,25)

example

the

is transferred must
If slist is used,

IGO

variable

slist.

specified),

following

control

the

which control
program unit.

member

FORTRAN-77,

executable

commas.

not

statement.

present

the

CONTROL

STATEMENTS

control

4.2

STATEMENTS

statements)

statement

statements

specified

Arithmetic

Logical

statement

Block

decision

evaluation

4.2,1

the

executes

condition

statement

met.

The

(or

three

block

types

based

statement

transfer

control

expression

Arithmetic

Statement

arithmetic

statements,

The

are:

The

transfers

arithmetic

1IF
the

(e)

sl,

arithmetic

statement
basis

transfers

the

value

statement

has

the

s2,

execute

contained

statement

the

control
an

statement.

one

arithmetic

three

expression.

form:

expression.

sl,s2,s3
Labels

executable

statements

the

same

All three labels (sl,s2,s3) are
required;
refer to three different statements.
The

arithmetic

zero,

passes to
label s3.
Some

control

label

statement

passes

s2;

evaluates
label

however,

expression

sl;

greater

1if

than

unit.

they

need

not

less

than

If
to

zero,

control

passes

examples:

THETA
IF

greater

than

4.2.2

(NUMBER/2*2-NUMBER)

Logical

logical

statement

IF
the

if the real
variable
CHI, to statement 100

CHI.
20,40,20

This statement transfers control
integer variable NUMBER is even,

The

e.
equal

zero,

This statement transfers control to statement 50
THETA is less than or equal to the real variable
if

program

to
to

statement
statement

40
20

if
if

the
the

value
value

of
the
is odd.

single

FORTRAN

Statement

statement
basis

conditionally
the

evaluation

4-4

executes
of

logical

expression.

CONTROL

The

logical
IF

(e)

statement

has

the

STATEMENTS

form:

logical

expression.

complete

FORTRAN

statement.

executable
statement
block IF statement, or

The

logical

value

statement

the

first

expression

1is

value of the expression
1is
executable
statement
after
executed.
Examples

Note
of

that

logical

.GT.

must

.OR.

(REF(J,K)

.NE.

HOLD)

4.2.3

statement

can

logical

statement

expression

logical

the

executed.

1If

the

next
not

groups)

block

false,
control
transfers
to
the
1logical IF, and statement
a

any

statement,

the
st

value.

statements:

LOGICAL

evaluates
true,

yield

The

except a DO statement, an END
another logical IF statement.

.LT.

GO TO

REF(J,K)

250
=

REF(J,K)*(-1.5D0)

ENDRUN

(ENDRUN)

CALL

EXIT

Block IF Statements

Block

statements

conditionally

execute

blocks

(or

statements.

The

four

These

block

ELSE

END

THEN

has

(e)

the

are

THEN

block

ELSE

block
END

(e)

used

form:

block
ELSE

are:

THEN

statements

construct

statements

THEN

1in

block

constructs.

The

CONTROL STATEMENTS

logical

expression.

block

A sequence of zero
sequence is called
Figure

4-1

describes

or more
<complete
a statement block.

the

flow of

control

FORTRAN

for

four

statements.

examples

This

block

constructs.

Each

block

statement,

associated

statement

expressions

block.

except

the

END

statement,

has

The statement block consists of all

the

statements following the block IF statement up to (but not
including)
the
next block IF statement in the block IF construct.
The statement
block is
conditionally
executed
based
on
the
values
of
logical

The

THEN

The

ELSE

that

IF statements.

block

IF construct.

exist:

1IF THEN statement

ELSE

construct
preceding

Except
ELSE

The

statement

1is

statement

block

that

for

specifies

the

optional

statement

The

value

true,

statement within a block

the

expression

construct

can

block

to be executed

1logical

optional

statement

the

no block

block

be executed

construct

if no

was

executed.

IF statement can

follow the

statement.

END

construct

ELSE

statement

can

IF THEN and

labels

cannot

statement

label

transferred

Section

terminates

executed

the

block

construct.

time

referenced.

to which control

only

from

within

describes

Section

each

4.2.3.3

THEN

END

can be

the

block

describes

nested

IF
IF

statement

loops

block

back

block

into

cannot

contains

terminal

statement
statement

block.

statements

blocks,

statement,

each

1loop

and

vice

a
IF

can

statement
constructs.

IF constructs.

Dblock
END
but

statement

can
contain
any
statement.
You
<can
you
cannot
transfer

blocks.

When

from one

statement

it must also contain the DO loop's

versa.

must

these
have

control

block

but
c¢an

You cannot transfer control

partially overlap

statement,
block.

the

another.

but

construct.

examples

block

labels,

statement

transferred,

restrictions on

4.2.3.2

describes

The

4.2.3.1
Statement
Blocks - A
statement
executable
FORTRAN
statement
except
an
transfer control out of a statement block,

control

1is
executed,
control
following
the
END
IF
block
in
a
block
IF
statement is executed.

ELSE statements can have statement
be

4.2.3.1

block.

within

block

END IF statement,

if the

and no preceding statement block

After the last statement in a statement
block
passes
to
the
next
executable
statement
statement.
Consequently, only one
statement

block

in the

true.

in the block IF construct was executed.
A
block
contain any number of ELSE IF THEN statements.

The

if the value of the logical expression

specifies

conditions

ELSE

block

begins

IF THEN statement

following

the

statement

construct

preceding

it is executed

following
IF

the

you

wholly

wuse

1loops

with

contained within one

CONTROL

STATEMENTS

Construct

Flow of Control

False

IF (e) THEN

block

True

END IF

Execute
block

Te& False
e

IF(e}) THEN
block,

True

block,
END IF
Execute
blOCk1

Execute
blOCk2

Execute
block

Execute
blocks,

IF (e,) THEN

Block,

ELSE IF (e;) THEN
block,
END IF

IF (1) THEN

blOCk1
ELSE IF (e;) THEN
blocky
ELSE IF (e3) THEN
blocks
ELSE
block

END IF

Execute
block,

Execute

block,

Execute
block,

ZK-206-81

Figure

4-1:

Examples

Block

Constructs

CONTROL STATEMENTS

4.2.3.2

Block

THEN

one

statement

the

executes

Examples
and

END

The

block.

(e)

block

this

example

construct

consists

construct conditionally

follows:

Example

Form
IF

simplest

statements;

THEN

(ABS(ADJU).GE.1.0E-6)

THEN

TOTERR=TOTERR+ABS
(ADJU)

block

QUEST=ADJU/FNDVAL
END

END

The

statement

and

the

The

END

block

consists

THEN

executed.

The

following

all

the

statements

between

the

THEN

logical
expression
e,
evaluates
value of e is true, the statement block
of e is false,
control
transfers
to
the
the block is
statement
after the END IF statement;
first

statement

executable

not

statements.

ABS (ADJU) .GE.1:0E-6.
is executed.
If the

If
value

example

the

shows

block

construct

with

ELSE

THEN

and

the

ELSE

statement:

Form

(el)

Example

THEN

blockl

.GT.

THEN

F=A-8B

ELSE IF (e2)
block?2

END

Blockl

THEN

ELSZ
D

END

consists

all

the

IF (A .GT.
= B/2.

statements

between

block2

consists of

ELSE

END

statements.

is greater

and

the

than

not greater

B blockl

than

B but

than

THEN

IF THEN statements;
THEN

B/2.)

all

the

THEN

statements between

the

executed.
A

greater

than

B/2,

block2

executed.

not

greater

blockl nor

block2

executable

statement

The

following

and

is executed;
after

example

the

shows

not

control
END

B/2,

neither

transfers directly to

greater

than

the next

statement.

block

construct

with

ELSE

and

ELSE

statement:

Form

Example

IF (e) THEN

IF (NAME .LT.

blockl

IFRONT

'N') THEN

IFRONT

FRLET (IFRONT)
=NAME (1:2)
ELSE

ELSE

block?2
END
Blockl

consists

statements;
and

the

IBACK=IBACK +
END

END

all

block2
IF

the

statements

consists

all

between

the

THEN

statements between

the

ELSE

statements.

the value of the character variable NAME is less than

executed.

'N',

blockl

CONTROL

the

value

NAME

greater

STATEMENTS

than

equal

executed.

The

following

THEN

example

statements

and

shows

ELSE

block2

block

(el)

construct

with

several

ELSE

statement:

Form
IF

'N',

Example

THEN

blockl

.GT.

THEN

F=A-B

ELSE

(E2)

THEN

ELSE

block2

F=A
ELSE

(e3)

THEN

ELSE

block3

.GT.

THEN

-2
_
(A .GT.

THEN

=C
IF

=12

F=A-12
ELSE

ELSE

block4
END

0.0

END

The above example contains four statement blocks.

all

the

statements

Block

between

the

Delimiting

blockl

THEN

block?2

First

block3

Second

block4

ELSE

and

ELSE
ELSE

and

than

END

Block

first

block

ELSE

THEN

listed

below.

THEN

second

and

Each block consists

statements

Statements

THEN and

ELSE

IF THEN

ELSE

greater

blockl

not

greater

than

but

not

greater

than

greater

than

executed.

greater

but

1is

than

block2

greater

than

executed.

block3

executed.

not

4.2.3.3
included

block4

executed.

Nested Block IF
Consructs - A
block
1in a statement block of another block

nested block IF
statement block;

The

following

construct
must
be
it must not overlap

example

contains

completely
contained
statement blocks.

nested

block

Form
IF

(e)

IF
construct
IF construct.

construct:

.LT.

100)

INRAN=INRAN
IF

(e)

THEN

blocka

blockl

ELSE
END

(ABS

(A-AVG)

INAVG

OUTAVG

END

.LE.

INAVG

OUTAVG

ELSE,

block2
END

THEN
+

5.)

ELSE

blockb
ELSE

within

Example

THEN

can
But

OUTRAN
END

OUTRAN +

THEN

be
the
a

CONTROL

STATEMENTS

If A is less than 100, blockl is executed.

block

IF construct.

the absolute

AVG

is less

or equal to 5, blocka is executed.

If the absolute value of

equal to 100, block2 is executed;

the

AVG

greater

executed

than

because

blockb

not

is executed.

nested

Blockl contains

value of A minus

A is greater

construct

than

nminus

than or

not

block2.

DO
4.3

STATEMENT

The DO statement specifies

statements.

statement,

and

iterative

processing

sequence

The sequence of statements is called the range of the DO
the

DO statement

together with

its

range

is called

loop.

The

DO statement

has

the

form:

v=el,e2[,e3]

sf{,]

The

label

must

of an executable

physically

unit.

statement.

the

This

executable

statement

in the same program

statement,

Usually an

integer variable but may be a real or double-precision

variable.

el,e2,e3

Usually integer expressions but may be real

double-precision

expressions.

The variable v

initial,

omit the

e2,

is called

terminal,

the control variable;

increment

increment parameter,

FORTRAN-77,

and

expressions

can be

are

parameters,

a default

el,

e2,

and e3 are

respectively.

increment value of

the

If you
used.

v can be a real or double-precision variable, and el,
any arithmetic

converted

expressions.

1If

necessary,

evaluated

the data type of the control variable

before they are used.
If the data type of
the
control
variable
|is
number of iterations of the DO range
the
double-precision,
or
real
might not be what is expected because of the effects of floating-point
rounding.

The label s identifies the terminal
terminal statement must not be:
e

A GO

statement

Any

END

RETURN

IF statement

arithmetic
block

statement

statement
statement

statement

statement of

the

1loop.

The

CONTROL

The

range

the

statement

statement,

STATEMENTS

consists

and

all

including

the

statements

terminal

that

statement.

The DO statement first evaluates the expressions el,
e2,
and
e3
to
determine
values for the initial, terminal, and increment parameters,
respectively.
The value of the initial parameter is assigned
to
the

control

wvariable.

loop

then

are

Section

The

number of
given by:

[(e2
where,

4.3.1.

executable

repeatedly.

executions

letting

integer

The

executed

whose

the

iteration

executed.

iteration

count

exact

range,

the

range

mechanism

called

the

iteration

represent

magnitude

the

does

count
If

the

zero

After

each
1.

Iteration

2.
3.

value
the

[X]
is
the
largest
magnitude of X and whose

the

negative,

compiler

negative,

The

iteration

the

[-3.5]

the

body

qualifier

the

body

=3).

the

loop

increment

count

to
for

range,

the

following

parameter

decremented

count

the
another

iteration

first

count

can

using

also

cause

statement

loop. If
«control
variable of the DO

and

the

executed

greater

execution

within

the

range

1is
transferred
statement remains

are

taken:

algebraically

added

than

statement

the

execution

control
after

the

statement

range.

statement

that

actions

executable

iteration

terminated.
You

The

1loop

specified

the

variable.

iteration

statement,

the

control

transferred

count,

Control

execution

The

expression,

exceed

X (for example,
be zero.
or

/NOF77

zero

above

not

once,

4.3.1

the

explained

e3)/e3]

sign is the same as the sign of
increment parameter, e3, cannot

not

statements

The

the

transfers

outside

the

defined

with

terminated

control

the
control

1loop,
its

outside

the
current

value.

When execution of a DO loop terminates, but other DO loops share
this
loop's
terminal
statement,
control transfers outward to the next DO
loop in the nesting structure (see Section 4.3.2).
If
no
other
DO
loop
shares
a
DO
loop's
terminal
statement,
or
if a DO loop is
outermost,

control

the

terminal

You

cannot

the

DO
altering

transfers

alter

1loop;

the

value

however,

first

executable

the

control

can

reference

variable

it.

cannot

this

the

you

The range of a DO statement
loops), as long as these DO
Section 4.3.2.
You

statement.

transfer

rule

are

control

described

can

contain

statements

into

the

other
meet

range

Sections

for

and

within

the

purposes

statements

certain

4.3.3

statement

range

other

loop.

than

(nested

requirements.

4.3.4.

after

DO
See

Exceptions

CONTROL STATEMENTS

You can modify variables holding the initial, terminal,

increment

parameters within the loop without affecting the iteration count.
Examples

statements

follow.

valid
DO

100

K=1,50,2

statement

This

specifies

iterations;

K=49

during

the

final

iterations;

J=-2

during

the

final

IVAR=5

during

the

final

iteration.
Do

350

J=50,-2,-2

specifies

statement

This

iteration.
DO

IVAR=1,5

specifies

This statement

1iterations;

iteration.
Invalid

is missing)

DO NUMBER=5,40,4

(the statement label

DO 40 M=2.10

(a decimal point has been typed for a comma)

Note

in the

that
DO40OM

invalid example,

last

the statement

2,10

is an unintentionally valid arithmetic assignment statement.

4.3.2

Nested

DO Loops

nested

A DO loop can include one or more complete DO loops called

loops.

The

range of the next outer loop.

statement.

—

Nested

loops

can

Fiqure 4-2 illustrates nested loops.

Correctly Nested
DO Loops

Incorrectly Nested
DO Loops

DO 45 K=1,10

DO 15 K=1,10

Dé 35 L=2,50,2

li:35 CéNTINUE

45 CONTINUE

Dé 25 L=1,20

—

15 CéNTINUE

Dé 30 M=1,15

Dé 45 M=1,20
L

range of a nested DO loop must lie completely within the

CONTINUE

L*30 CéNTINUE
Figure 4-2:

Nested DO Loops

4-12

terminal

CONTROL

4.3.3

Control

Within

outer

loop

two

Transfers

nested
an

loop,

loop;

inner

therefore

4.3.4
A

is
is

can

transfer

you

cannot

loops

to
this
innermost

the

same

shared
loop.

inner
from

loop
outer

terminal

statement,

terminal statement
Because this shared

you

only from
terminal

any transfer to it
to an inner loop,

from
and

an
is

Range

out

extended

the

range

1loop

1if

and

control

statement

The

includes

range

this

destination
control

following

loop

statement
to

the

rules

control

then,

another

The

invalid.

loop has

returns

from

control

loop.

statements,

the

control

transfer

part
of the innermost loop,
transfer from an outer loop

Extended

control

Loops

you

nested

however,

can
transfer
«control
within the range of the
statement
outer loop

STATEMENTS

the

after

returns

all

first

statement

execution
control

executable

transfer

and

transfers
one

into

statements
the

the

more
1loop.

between

statement

that

loop.

govern

the

use

statement

with

extended

range:

transfer

from
®

its

into

the

extended

Statements

the

range

statement

extended

range

must

not

variable.

Figure 4-3
transfers.

illustrates

valid

and

1invalid

vValid
Control

—

Gé TO 20
15

CONTINUE

A=B+C

Loop

control

A;B+C

D=E/F

CONTINUE

X=A*D

M=1,15

D=E/F

X=A*D

CONTINUE

Figure

GO TO 40

range

Transfers

GO TO 50

CONTINUE

Range

control

DO 35 L=2,20

M=],15

4-3:

only

the

DO 50 K=1,10

Extended

change

extended

Control

K=1,10

DO 15 L=2,20

permitted

Invalid

Transfers

range.

Control

Transfers

4-13

and

Extended

Range

CONTROL STATEMENTS

CONTINUE

STATEMENT

CONTINUE

4.4

The

CONTINUE

statement

transfers

control

the

executable

used as the terminal statement of a DO
primarily
is
It
statement.
loop that would otherwise end with a prohibited control statement such

as
The

GO TO or
CONTINUE

arithmetic

statement has

IF.
the

form:

CONTINUE

CALL

4.5

CALL STATEMENT

The CALL statement executes a SUBROUTINE subprogram or other

external

can also specify an argument list for the subroutine.

procedure.

(See Chapter 6 for detail on the definition and use of a subroutine).
following

The CALL statement has the

form:

CALL s[([all,[al]l...)]
s

The

name

dummy

other

SUBROUTINE

subprogram or

other

external

procedure,

argument associated with a SUBROUTINE subprogram or

external

procedure.

actual

argument.

(Section

6.1

describes

actual

arguments.)

If you specify an argument list, the
CALL
statement
associates
values
in
the
1list
with the dummy arguments in the subroutine.

then transfers control

the

first

executable

the
It
the

order,

and

statement

subroutine,

The

arguments

the

CALL statement must agree

number,

data type with the dummy arguments in the subroutine.
These arguments
can
be
variables,
arrays,
array
elements,
substring
references,
constants,
expressions,
Hollerith constants, character constants, or
subprogram names.
An unsubscripted array name in
the
argument
list
refers

Examples

the
of

entire

CALL

CALL CURVE
CALL

PNTOUT

CALL

EXIT

array.

statements

are:

(BASE,3.14159+X,Y,LIMIT,R(LT+2))
(A,N,'ABCD')

CONTROL

STATEMENTS

RETURN

4.6

RETURN

STATEMENT

The

RETURN

statement

the

calling

program.

used

return

has

the

form:

control

from

subprogram

RETURN

When

RETURN

returned

Chapter

statement

6).

the

When

executed

statement

RETURN

that

statement

function

the

1is

subprogram,

executed

the

control
reference (see

function

first

subroutine

executable

statement

example:

SUBROUTINE

statement

subprogram,
control
1is
returned
following the CALL statement.
RETURN

contains

SIZCHK
10,20,30

(N)

(N,K)

K=-1
RETURN

K=0

K=+1

RETURN
RETURN
END

PAUSE
4.7

PAUSE

The

PAUSE

displays
The

STATEMENT

statement

PAUSE

message
statement

PAUSE

temporarily

the

has

suspends

terminal

the

program

permit

you

execution
and
some action.

take

form:

([disp]

disp
An

alphanumeric

digits,
The

disp

depends

batch
and

argument
on

job,

the

how

the

your

If the program
are
displayed

not

the

decimal

optional.

disp

The
being

are

digit

string

effect

executed.

written

a
If

one

the

system

in interactive mode,
terminal,
followed

the
by

program

suspended.

After

you

five

PAUSE
statement
is running as a

suspended.

is running
at
your

that

constant.

program

contents

program

indicating

literal,

octal

output

contents
prompt

then

file,

of
disp
sequence

enter

the

proper
control
command,
execution resumes with the first executable
statement following the PAUSE.
The proper control command is specific

the

Some

operating

system

examples

PAUSE

999

PAUSE

'MOUNT

PAUSE

(refer

statements

TAPE'

the

are:

PDP-11

FORTRAN-77

User's

Guide).

" CONTROL STATEMENTS

STOP

STOP STATEMENT

4.8

The STOP statement terminates program execution and returns control to
system.

the

operating

The

STOP statement has the

form:

[disp]

STOP
disp

digit

string

one

if present, specifies a

message

The END statement marks the end of a program unit.

must

A character constant, a decimal
digits,

an octal

The disp argument,
when

execution

Examples

constant.

five

displayed

stops.

STOP

'END OF

statements

are:

RUN'

STOP

END

4.9

END STATEMENT

last source line of every program unit.

The

END statement has

the

must

not

execution

from

form:

END

The END statement must not occur on a continuation line and
itself be continued.

In a main program,

reaching

the END

STOP

statement,

statement

program

prevents

execution

terminates;

subprogram, a RETURN statement is implicitly executed.

in a

CHAPTER
SPECIFICATION

Specification

allocate

statements

and

characteristics
The

specification
e

the

STATEMENTS

nonexecutable

variables

symbolic

statements

IMPLICIT

statement

symbolic
e

are

initialize

names

statements

and

arrays,

used

the

that

1let
you
define
other

and

program.

are:
--

specifies

the

implied

data

type

Type

declaration

type

statement -- explicitly
symbolic names

specified

DIMENSION

statement

array,

and

the

COMMON

statement

number

declares

the

declares

the number of dimensions
elements in each dimension

reserves

one

contiguous

VIRTUAL

be
e

statement

two

OAVE

statement

execution

INTRINSIC

FORTRAN

DATA

PARAMETER

statement

one

the

specified

one

arrays

1location

entity

symbolic

names

functions
initial

values

before

program

execution

statement

storage

subprogram

names
declares

status

assigns

elements

same

definition

statement

declares

intrinsic

the

RETURN

for

storage

associates

retains

procedure

statement

array

space

program

entities

statement

external

and
e

EXTERNAL

be
e

reserves

normal

EQUIVALENCE

be
e

outside

with

after
e

statement

located

data

areas

storage

names

assigns

symbolic

variables,

name

arrays,

constant

main

program

value
e

PROGRAM

statement

assigns

symbolic

name

unit
®

BLOCK

in
in
The

DATA

which
common

following

statement

initial
blocks

sections

values

describe

establishes

may

these

BLOCK

assigned

statements.

DATA

program

entities

unit

contained

SPECIFICATION

STATEMENTS

IMPLICIT
IMPLICIT STATEMENT

5.1

The IMPLICIT statement permits you to change the

default

are

all

with

interpreted to be of integer data type,

and

IMPLICIT statement allows you to alter these

The

the

IMPLICIT statement has
IMPLICIT

names

beginning

letter are interpreted to be of real data type; the

other

any

data-typing

default, all names beginning with the letters I through N

rules.

interpretations.

form:

typ(al,al...)[,typ(al,al...)]...

typ
One of

the data-type

alphabetic

specifiers.

specification

(See Table

one of

two

2-2.)

forms:

cl-c2,

The cl-c2 form specifies a
is an alphabetic character.
¢
where
in
occur
that must
<¢2),
through
¢l
(from
range of letters
order.

alphabetical

The IMPLICIT statement assigns the specified data type to all symbolic
begin with any of the specified letters and that have no
that
names
explicit data-type declaration.
over implicit declarations.

Explicit declarations

The IMPLICIT statement
also
affects
symbolic
PARAMETER statement (see Section 5.11).
For

example,

the

take

names

precedence

defined

statements

IMPLICIT

INTEGER

IMPLICIT

REAL

(I,J,K,L,M,N)

(A-H,

0O-Z)

specify the default in the absence of any explicit statement.

statements
specification
other
IMPLICIT statements must precede all
except
PARAMETER
statements,
and
they
must precede all executable
statements.

You can

use

character
is

the

data

default

IMPLICIT statement to

type;

length.

Typ must

positive

integer constant

Any data

type

following

can be

examples

IMPLICIT

set a

default

unsigned

in parentheses,

specified

DOUBLE

PRECISION

(S,Y),

(D)

LOGICAL*1

integer

in the range

IMPLICIT

demonstrate:

IMPLICIT COMPLEX

1length

for

the

simply specify typ as CHARACTER*len, where len

(L,A-C)

constant

1 through

statement,

255.

the

SPECIFICATION STATEMENTS

TYPE DECLARATION
5.2

TYPE

DECLARATION

STATEMENTS

Type
declaration
statements
specified
symbolic
names.
statements:

character
The

numeric

type

following
e

declarations

declarations
rules

Type

type

apply

(see

declaration

explicitly
define
There
are two forms

Section

type

(see

Section

5.2.1)

and

5.2.2).

declaration

statements

the
data
type
of
of type declaration

must

statements:
precede

all

executable

statements.

5.2.1
The

The

data

type

You
by

can use a
appending

array

name.

Numeric

Type

numeric

type

type
an

symbolic

name

can

declared

only

once.

declaration statement to declare
an
array
declarator (see Section 2.5.1)

Declaration

declaration

array
to an

Statements

statement

has

the

form:

typ v([,v]
typ
Any data

The

type

symbolic

function

specifier

name

subprogram,

symbolic name can
form
*s,
where
s
being declared (see

(see

Table

wvariable,

2-2)

except

array,

CHARACTER

statement

function,

array declarator.

followed by a data-type length specifier of the
is one of the acceptable lengths for the data type
Table 2-2).
©Such a
specification
overrides
the

length
attribute that the statement implies, and assigns a new length
to the specified
item.
If
you
specify
both
a
data-type
1length
specifier and an array declarator, the data type length specifier goes
first.
Examples of type declaration statements are:

INTEGER COUNT,
REAL

MATRIX(4,4),

SUM

MAN, IABS

LOGICAL

SWITCH

INTEGER*2

REAL*8 WX1l,

M12%*4,

WX3*4,

IVEC*4(10)

WXS5,

WX6*8

5~3

SPECIFICATION STATEMENTS

Character Type Declaration Statements

5.2.2

Character

type

declaration

CHARACTER[*1len[,]]

statements

have

the

form:

v[*len][,v[*1len]]...

The symbolic name
of
a
constant,
variable,
array,
or
array
declarator.
(You
cannot
declare
a
function
subprogram,
a
statement function, or a virtual-array name to
be
of
character
data

type.)

len

unsigned

the

enclosed

1in

integer constant or

parentheses.

character

data

integer-constant

The value of

its own length

length

elements.

If
you
specify
CHARACTER*len,
len
becomes
specification
for
the
specified list.,
If an

not have

expression

len specifies the

specification,

the

the
item

default
length
in this list does

item's

1length

len.

However,
if
an
item
does
have
1its own length specification, this
specification overrides the default length specified in CHARACTER*len.
If

you do not

specify a

length,

length of

assumed.

The

1length

specification
must
be in the range 1 to 255;
a length specification
of zero
1is
1invalid.
You
can
use
a
character
type
declaration
statement to define arrays by including array declarators (see Section
2.5.1)

length,

numeric

the

type

Examples of

list.

you

specify both

array declarator goes

declarations).

character

type

declaration

CHARACTER*32 NAMES (100),
This

statement

specifies

first

SOCSEC

array

LAST,

FIRST

array

declarator

and

(the reverse of the rule

statements

for

follow:

(100)*9,

NAMETY*10

NAMES

comprising

one

hundred

32-character
elements,
an
array
SOCSEC
comprising
one
hundred
9-character elements, and a variable NAMETY, which
1is
10
characters
long.
PARAMETER

(LENGTH=4)

CHARACTER®* (4+LENGTH)

The latter statement specifies two
8-character
wvariables,
LAST
FIRST.
(The PARAMETER statement is described in Section 5.11.)
CHARACTER

This

LETTER(26)

statement

l-character

specifies

This statement
and

expression.

array

LETTER

comprising

twenty-six

elements.

CHARACTER*16

large,

and

the

BIGCHR*(30000*2) ,QUEST*(5*INT (A))

invalid;

the value

length specifier

for

specified

QUEST

for

is not an

BIGCHR

integer

1is

too

constant

SPECIFICATION

STATEMENTS

DIMENSION
5.3

DIMENSION

The

DIMENSION

and

the

The

DIMENSION

STATEMENT

statement

number

specifies

elements

statement

DIMENSION

has

the

each

the

number

dimension.

dimensions

array

form:

a(d)[,a(d)]...

a(d)
An

array

declarator

(see

Section

2.5.1).

The

symbolic

name

array.

A dimension

The

DIMENSION

each

the

length

The

total

the

statement

dimension
of

the

number

product

example,

the

defines

ARRAY
MATRIX

addition

array.

one storage element
The data type of the

unit,

Examples

elements

array's

assigned

individual

ARRAY (4,4),

having

DIMENSION

you

(4x4)

125

statements,

COMMON,

can

DIMENSION

real

(5x5x5)

use

and

elements

array

equal

declarators.

statements

name

to
For

MARK(4,4,4,4)

arrays

can

array

statements.

only

one

each
bytes

and
each.

declarators

However,

array

within

declarator.

are:

DIMENSION

bytes

use

BUD(12,24,10)

information

you

VIRTUAL

array

elements

X(5,5,5),Y(4,85),2(100)

2.5.

integer

DIMENSION

further

dimension

MATRIX(5,5,5)

DIMENSION

Section

to each
element
array determines

element.

storage

the

declaration,

program

For

allocates

statement

defines
In

storage

DIMENSION

type

declarator.

and

storing

array

elements,

see

SPECIFICATION

STATEMENTS

COMMON

5.4
A

COMMON

STATEMENT

statement

reserves

one

contiguous

blocks

storage.

A
symbolic
name is used to identify each contiguous block;
however,
you can omit a symbolic name for a blank common
block
in
a
program
unit,
COMMON
statements
also
specify
the
order of variables and
arrays

The

each

COMMON

common

statement

COMMON

block.

has

[/[cb]l/]

the

form:

nlist[[,]1/[cb]l/

nlist]...

symbolic

(If

the

name,

first

called

c¢cb

1is

common

blank,

block

you

name;

can

<c¢b

omit

can

the

blank.

first

pair of

slashes.)

nlist
A

list

variable

separated
COMMON

common

names,

commas.

array

names,

(You cannot

use

and

array

block

can

When

common blocks
programs
are made
become

following

in a

statement.)

have

the

same

name

variable

same
executable
program.
However, it cannot have the
function, subroutine, or entry in the
same
executable
Section 2.1).

names

declarators

virtual-array name

having

the

part

the

associated

with

array

same name
program

the

as a
(see

same
name
but
1located
1in
separate
same executable program, the individual

the

same

storage

area.

Consider

the

with

example:

PROGRAM

MAIN

COMMON/BLOCK1/ICOUN, IHOL/BLOCK2/ICHK (10)

CALL

GSUB

END

SUBROUTINE

GSUB

COMMON/BLOCK2/JCHK
(10) /BLOCK1/JCOUN, JHOL

END

this

the
a

example,

same

single

storage
storage

You can have
you can have

BLOCK1l

area;

MAIN

and

likewise,

BLOCKl

the

two

GSUB

are

associated

BLOCK2s

are

associated with

area.

only one blank common block in
up to 250 named common blocks.

executable

program,

but

SPECIFICATION

Entities

are

above

the

storage

assigned

space

respective

storage

example,

ICOUN

BLOCKl,

because

STATEMENTS

common blocks on a one-for-one basis.
JCOUN are associated with the same

and

each

entity

occurs

first

list.

Entities placed in a one-to-one
correspondence
in
the
block
should
agree
in
data type.
For example, if one
contains the statement
COMMON

and

program

INTEGER*2
COMMON

must

results

not

unit

contains

may occur

common

block

allocated

for

integer
of

assign

the

when

such

odd

numeric

byte

Examples

COMMON

Main
COMMON

COMMON

data

program

variables

that

character

subsequent

boundary.

The

data

compiler

blocks:

type

statements

The

data

entirely

combined,

correspond

are
mix

COMMON

the

arrays

other

supplies

character

any

however, all common blocks
In addition, you must
not

type

filler

begun on a
character

block

data

must

type.

follow.

Program

Subprogram

HEAT,X/BLK1/KILO,Q

SUBROUTINE
COMMON

FIGURE

/BLK1/LIMA,R/

/ALFA,BET

RETURN

END

COMMON

are

(BYTE)

common

units
to

way

blocks;
boundary.

these

MONEY is made
variable CENTS.

real

LOGICAL*1

entirely

The

statement

variable

common

word (even byte)
and numeric data

CALL

common
program unit

MONEY

space

same

MONEY

because the 2-byte
high-order 2 bytes
You

its

CENTS

another

incorrect

statement in
and puts

block,

the main
KILO and

program puts
Q in a named

HEAT and X
in
a
blank
common block, BLKl.
The

COMMON statement in the subroutine makes ALFA and
BET
correspond
to
HEAT
and X in the blank common block, and makes LIMA and R correspond
to

KILO

and

BLK1.

valid

Invalid

INTEGER

CHARS (9)

CHARACTER

COMMON/STRING/ILEN, CHARS

this

block

example,

BYTE

the

character

integer

CHARS (9)

COMMON/STRING/CHARS, ILEN

variable

ILEN

allocated

ILEN

allocated

the

same

variable.

BO,Bl

COMMON/STRING/BO, ILEN,B1

this

address.

example,

the

integer

variable

odd

byte

SPECIFICATION

STATEMENTS

VIRTUAL
5.5

VIRTUAL

A virtual

STATEMENT

array

array whose

storage

1is

allocated

main memory outside of the program's directly addressable
The use of virtual arrays in
a
program
frees
directly
memory

for

executable

The

VIRTUAL

dimensions

VIRTUAL

code

statement

and

statement

VIRTUAL

other

virtual

names

the

has

a(d)

and

number

the

data

physical

main memory.
addressable

storage.

array

and

elements

specifies

each

the

number

dimension.

The

form:

[,a(d)]...

a(d)
An

array

declarator

(see

Section

2.5.1).

The

symbolic

name

array.

d
A

The

dimension

maximum

declarator.

total

directly

programs
executing
on
65,536 bytes.
In light

arrays,
can

32,767

used

easy

up.

elements

LOGICAL*]1

array

see

numeric

from

64K

limit

addra2ssable

computer
in
the allowable

how

quickly

array,

byte

storage
space,
and
would require 262,136
the

a
of

to
per

for

bytes

element

memory

directly

addressable

instance,
in

addressable

can

length.

would

have

user

is 64K, or
FORTRAN-77

main

memory

maximum

Therefore,

require

a
maximum
COMPLEX array
bytes of storage space, a

directly

available

the PDP-1l1 family
sizes
of
PDP-11

32,767

maximum

bytes

of 8 bytes per element
requirement far beyond

memory.

NOTE

Virtual
arrays
RSTS/E operating

The data type
data
type of

the

first

are
not
systems.

of a virtual array
any other array is

letter

the

name,

supported

is specified in
specified, that

explicitly,

the
is,

same way that the
either implicitly

type

declaration

statement.

example

VIRTUAL

This

A(1000),

statement

elements,

VIRTUAL

statement

follows:

LARG(180,180),

defines

two-dimensional

Mult

(4,4,4,4,4,4,4)

one-dimensional

array

named

LARG

named

32400

elements,

1000
and

SPECIFICATION

STATEMENTS

seven-dimensional array named MULT of 16384
elements.
are
placed in external main memory and therefore do not
diminish the 64K of directly addressable memory.

These
arrays
significantly

For

storage,

further information
Section 2.5.

5.5.1

Restrictions

Virtual arrays
limitations:

and

A virtual
(see

The

name

array

used

virtual

Using

virtual

Section

concerning

arrays

Virtual

array

name

their

not

are

subject

used

a
an

Virtual

COMMON

arrays

The

name

following

statement

array or virtual array element must
EQUIVALENCE statement (see Section 5.6).
or

virtual

DATA

cannot

array

element

statement
be

used

(see
to

cannot

Section

contain

specifications (see Section 8.6).
The name
or virtual array element must not appear as

I/0

the

virtual

array

value

5.4).

initial

see

Arrays

elements

must

and

not

assigned

5.10).
run-time

format

of a virtual array
a format specifier

statement.

virtual

be
specified
as
parentheses) of an
Anl) [

the

array or
buffer

ENCODE

virtual array element must
not
argument (third argument inside
DECODE

statement

(see

Section

The name of a virtual array element must not
be
used
as
an
actual
argument
to
a subprogram if the subprogram assigns a
value to the corresponding dummy argument (see Section 6.1).
The

name

used

Section
The

Below

virtual

specify

array

the

name

virtual

array

keyed

I/0

A virtual

array

name

must

examples

VIRTUAL

valid

and

not

A(1000),B(2000)

WRITE (2,*)

SUB

invalid

READ (1,*) A
DO 10,I=1,1000
B(I)=-A(I)*2
CALL

array

cannot be
statement.

valid

virtual

keyword

element

OPEN

cannot

statement

(see

9.1.10).

expression

are

FILE

(A(I),I=1,1000)
(A,B)

of
use

used

data
of

specify

type

character.

virtual

arrays:

key

SPECIFICATION

STATEMENTS

Invalid
VIRTUAL

A(10)

CHARACTER A

(declared

COMMON

/X/

EQUIVALENCE

WRITE (1,A)

(used

type character)

X,Y

Virtual Array References

COMMON statement)

(used as

format specifier)

(used in EQUIVALENCE statement)

(A(1l),Y)

ENCODE (4,100,A(3))

5.5.2

(used in DATA statement)

DATA A(l1)/2.5/

(used as ENCODE output buffer)

in Subprograms

array can become
wvirtual
name of a
A dummy argument that is the
name of a virtual
the
also
is
that
argument
actual
an
with
associated
array.

An actual argument that

is a

can

reference to a virtual array element

become associated only with a dummy argument that is a simple variable
wvirtual
a
is
1In effect, an actual argument that
(see Section 2.4).
array element is treated as if it were an expression.
Furthermore, a value must be

before

this

must not alter

assigned

virtual

array

element

element is used as an actual argument and the subprogram
the value of the corresponding dummy argument.

Below are examples of valid and invalid virtual

array

references

subprograms:

Valid

Usage

VIRTUAL A(1000),B(1000)
B(3)=0.5

CALL

SCALE (A,1000,B(3))

END

SUBROUTINE

SCALE

(X,N,W)

VIRTUAL X (N)
5=0
po 10,

I=1,N

S=S+X(I)*W
TYPE

*,S

END

Invalid

Usage

VIRTUAL A(1000)
REAL

B(4000)

CALL ABC(A,B,A(3))
END

SUBROUTINE

ABC(X,Y,2)

REAL X (1000)

VIRTUAL Y (4000)
Z=2.3
END

(actual

argument is virtual)

(actual argument is nonvirtual)
(actual argument is virtual
element)

array

SPECIFICATION

STATEMENTS

EQUIVALENCE
5.6

EQUIVALENCE

STATEMENT

The EQUIVALENCE
entities in the

statement partially or
same program unit with

The

statement

EQUIVALENCE
EQUIVALENCE

(nlist)

has

the

totally associates two or
the same storage location.

form:

[,(nlist)]...

nlist
A

1list

variables,
array
elements,
arrays,
or
references,
separated by commas.
You must
of these entities in each list.

substring
least two

The

EQUIVALENCE

location
In

statement

all

the

EQUIVALENCE

substring

allocates

entities

statement,

reference

must

used

arguments,

virtual

EQUIVALENCE

storage
its

each

expression.
Dummy

arrays,

begins

the

same

list.
expression

integer

and

that

character
specify at

constant

virtual

statement.

array

subscript

integer

elements

may

not

The

entities in nlist must be either entirely of numeric data type
entirely of character data type:
you cannot make numeric entities
character entities equivalent.
You must
a

way

byte
An

not

equivalence

that

subsequent

data

LOGICAL*1

used

EQUIVALENCE

arrays

any

with

other

boundary.

array

name

You

equivalence

can

is,

you

the

element

can

variables

store

them

such

different

that

you can store
component
of

example, if you make an
variable,
the
integer
the complex variable.

integer
variable

statement

other
is

elements

allocated

refers

valid

and

invalid

numeric

each

data

entity

in
on

such
an

odd

types;

that

begins

the

one
type.

variable
equivalent
to
a
shares storage with the real

statements

or
and

first

multiple components of
a
higher-ranked data

EQUIVALENCE

the

array.

address.
Furthermore,
type
with
a
single

Examples

type

constant

same

data
For

complex
part of

are:

valid
DOUBLE

PRECISION

INTEGER*2

This
array
DVAR.

DVAR

IARR(4)

EQUIVALENCE

(DVAR,IARR(1))

EQUIVALENCE

statement

IARR

occupy

CHARACTER

the

KEY*16,

EQUIVALENCE

makes

same

the

storage

STAR*10

(KEY,STAR)

5-11

four
as

the

elements

the

integer

double-precision

variable

SPECIFICATION STATEMENTS

character

This EQUIVALENCE statement makes the first character of the

variables KEY and STAR share the same storage location.
the substring KEY

variable STAR is equivalent to

(1:10).

The character

Invalid
LOGICAL*1

BYTES(10)

(ILEN,

EQUIVALENCE

BYTES(8))

In the above example, the integer variable ILEN is allocated on an odd

byte

address.

Making Arrays Equivalent

5.6.1

When you make an element of one array equivalent to an element of
the EQUIVALENCE statement also sets equivalences
another array,
the
1f
Therefore,
between corresponding elements of the two arrays.
both
equivalent,
made
are
arrays
equal-sized
two
of
first elements
third
the
And, for example, if
arrays share the same storage space.
element
first
the
to
equivalent
made
is
array
element of a 7-element
first array overlap
of another array, the last five elements of the
the first

five elements of the second array.

You must not use the EQUIVALENCE statement to assign the same

storage

You also must not
location to two or more elements of the same array.
with
inconsistent
is
that
way
a
in
locations
memory
attempt to assign
For example, you cannot
the normal linear storage of array elements.

make the first element of one arrav equivalent to the first element of

another

and

array

attempt

then

set an equivalence between the
the

second element of the first array and the sixth element of

other

array.

Some examples of the use of the EQUIVALENCE statement follow:
DIMENSION TABLE
EQUIVALENCE

(2,2),

TRIPLE

(TABLE(2,2),

(2,2,2)

TRIPLE(1,2,2))

As a result of these statements, the entire array TABLE shares part of
Figure 5-1 shows how
the storage space allocated to array TRIPLE.
these statements align the

arrays.

Array TABLE

Element

Array

Number

Element

Figure

OC~Jaun
b WN

TRIPLE (1,1,1)
TRIPLE(2,1,1)
TRIPLE (1,2,1)
TRIPLE(2,2,1)
TRIPLE(1,1,2)
TRIPLE (2,1,2)
TRIPLE (1,2,2)
TRIPLE (2,2,2)

5-1:

Array

Element

Number

W N

Array TRIPLE

TABLE (1,1)
TABLE (2,1)
(1, 2)
TABLE

TABLE (2,2)

Equivalence of Array

Storage

SPECIFICATION

Each
in

the

Figure

You

following

statements

STATEMENTS

also

aligns

EQUIVALENCE

(TABLE,TRIPLE(2,2,1))

EQUIVALENCE

(TRIPLE(1,1,2),

can

identify

single
though

the

two

arrays

shown

5-1:

subscript
the

statement

array

element

(that

1is,

aligns

TABLE(2,1))
in

with

EQUIVALENCE

the

1linear

multidimensional.

arrays

TRIPLE

and

For

TABLE

statement

element

example,

they

are

with

number),
the

even

following

aligned

Figure

5-1:
EQUIVALENCE

Similarly,
For

can make

example,

values.

sequence,

you

can

(TABLE(4),

use

whole

array B.

make

the

statement

array

A now

with

A(2:3,4)

refers to

array A(2:3,4)

the

nonunity lower
is

sequence

third

storage

with

element
array

part

how the

above

the

storage

statement

Array

space

aligns

Array

Element

Array

Element

Number

Element

Number

B(2,1)

B(3,1)

B(4,1)

A(2,1)

B(2,2)

A(3,1)

B(3,2)

A(2,2)

B(2,3)

A(2,3)
A(3,3)

B(4,3)

A(2,4)

B(2,4)

A(3,4)

B(3,4)

B(4,4)

Figure

Making

the

B(2:4,4),

allocated

the

arrays.

A(3,2)

5-2:

eight

Element

B(3,3)

B(2,4))

5-2 shows

B(4,2)

bounds.
of

‘

(A(3,4),

Figure

equivalent

defined

Array

5.6.2

arrays

array

A reference to A(2,2)

EQUIVALENCE

The

TRIPLE(7))

Equivalence of Arrays with Nonunity Lower

Bounds

Substrings Equivalent

When you make one character substring equivalent to another
character
substring,
the
EQUIVALENCE
statement also sets equivalences between
the other corresponding characters in the character entities.
For

example,

CHARACTER

result

NAME*16,

EQUIVALENCE

statements

ID*9

(NAME (10:13),

ID(2:5))

the character variables NAME and
Figure

5-3.

space

illustrated

SPECIFICATION

The

following

aligned

statement

Figure

EQUIVALENCE

the

Character
For

substring

CHARACTER

character
Figure 5-4.

NAME

and

are

array

arrays

result

equivalences

the

they

are

complete

can

FIELDS

the

the
other

arrays.

overlap

any

character

©position.

STAR(5)*5

(FIELDS(l) (2:4),

arrays

elements,

between

statements

FIELDS(100)*4,

EQUIVALENCE

the

references

sets

characters

elements

example,

arrays

(NAME(9:9),ID(1:1))

statement

corresponding

aligns

5-3:

character

EQUIVALENCE

also

STATEMENTS

and

STAR(2) (3:5))

STAR

storage

space

shown

NAME
Character
Position
1

2
3
4

5
6

ID
Character

Position

oljlo|l~Nj]OO]jO]Is»x]lWIMN

9
10
11

12
13

14
15

ZK-207-81

Figqure

You

cannot

use

the

positions

the

same

You

cannot

use

also

The

following

way

Equivalence of

EQUIVALENCE

location

locations in
of character

two

5-3:

character

variable

EQUIVALENCE

inconsistent

and

statements

that

the

that

variables

statement

substrings

Substrings

assign

start
or

character

statement

with

the

same

different

storage

character

array.

normal

assign

linear

memory
storage

arrays.

also

EQUIVALENCE

(A,B(4,1))

EQUIVALENCE

(B(3,2),

align

A(2,2))

the

arrays

shown

Figure

5-2:

SPECIFICATION

STATEMENTS

STAR
Character

Position
1

Subscript
1

2
3

FIELDS

Subscript

C;:sriaticc}r?r

1
2
3
4

1
2

AAYA
100

1
2

3
4

ZK-208-81

Figure

5-4:

Equivalence of Character Arrays

5-15

SPECIFICATION STATEMENTS

Extending Common Blocks

5.6.3

common

entities

stored

the

EQUIVALENCE

statement.

is, you can only extend it beyond the last element of

the

previously

before the first element of the existing common block.

The

following

When you make entities equivalent

block, the common block can be extended beyond its original boundaries
to include

However,

the

entities

specified

you can extend the common block in only one direction,
common

established

cannot

You

block.

place

That

the extended portion

examples show valid and invalid extensions of the common block:

valid

A(l) ]| A(2) | A(3) | A(4)

DIMENSION A(4),B(6)
COMMON

EQUIVALENCE

(A(2),B(1))

B(1) | B(2) | B(3) | B(4) | B(5) | B(6)
.

__J\

Extended
Portion

Existing
Common
Invalid

COMMON A

EQUIVALENCE

B(1)|

(A(2),B(3))

B(2)|

Extended

Portion

If you assign two entities to common

equivalent

A(4)

A(l) | A(2) | A(3)|

DIMENSION A(4),B(6)

B(5) | B(6)

B(4)|

B(3)|

——
Existing Common

blocks,

you

D N
Extended
Portion

cannot

make

them

each other.

SAVE

5.7

SAVE STATEMENT

The SAVE statement retains the definition status of
an
execution of a RETURN or END statement in a subprogram.
The

SAVE statement has

SAVE

the

entity

after

form:

[a[,al...]

A unique common-block name
variable

name,

(preceded and followed by a slash),

array name.

Dummy argument names, procedure names, and names of entities contained

common blocks must not appear in a SAVE statement.

these restrictions, a multiple definition of the name

If you violate

wused

illegally

SAVE

statement

occurs.

An entity contained

in a common block specified

does not become undefined upon execution of a RETURN or END statement
undefined
However, it may become
contained in the same program unit.
(or redefined)

in another program unit.

SPECIFICATION

Because
one

variable,

overlay

segment

array

can

by another
useful
in
you

SAVE

statement,

SAVE

program

unit

The

common

does

SAVE
the

block

this

contained

segment

replaced

SAVE
statement
can
be
especially
To retain the definition of an entity
can simply specify that entity
in
a
proper program unit.
not

list

the

common

when

explicitly

consisting

SAVE

contain

statement

all

list

allowable

treated

items

resides.

the

name

is specified
in
a
SAVE
statement
within
a
executable program, this common block name must be
statement in every subprogram in which the
common

an
SAVE

example

DIMENSION

SAVE

which

appears.

following

The

that

block

COMMON

the

contained

subprogram
of
specified in a

block

within

statement

though

undefined

overlay segment,
the
overlaid
programs.
are using overlays, you

when

element,

become

STATEMENTS

demonstrates

use

the

SAVE

statement:

A(100)

/CMN2/B(100),C,D(50)

A,/CMN2/,E

statement

array

the

this

named

example
common

preserves

block

the

CMN2,

current

and

the

definitions

local

variable

EXTERNAL
5.8

EXTERNAL

The

EXTERNAL

arguments

STATEMENT

statement
other

allows

you

use

external

subprogram

names

subprograms.

The

subprograms to be used as arguments can never be FORTRAN intrinsic
functions;
they can only be user-supplied functions and subroutines.
The INTRINSIC statement discussed
in
Section
5.9
allows
intrinsic
function

The

names

EXTERNAL

The

EXTERNAL

the

actual

Note

Appendix

(A,

from
A

form:

for

user-supplied
with

declares
a

function

C),

the

each

the

earlier

name

the

name

subprogram.

name

included

name

can

used

can

use

CALL

used

example
reference

EXTERNAL

earlier

This

that

reference

for

symbolic

reference

complete function
statement.

that

subprogram,

the

procedure.

subprogram

function

FUNC(B),

interpretation

different

the

external

complete

SUBR

subprogram.
A
in an EXTERNAL
The

argument

that

arguments.

associated

statement

name

argument

CALL

has

name

argument

used

v([,v]...

symbolic

dummy

statement

EXTERNAL

The

-is

interpretation.

the

corresponding

statement.
an

argument

represents
not,

statement
versions
of

then

FUNC(B)

value,

therefore,

not

defined

described
above
DIGITAL FORTRAN.

is
See

SPECIFICATION STATEMENTS

INTRINSIC
5.9

INTRINSIC STATEMENT

The INTRINSIC statement allows you to use intrinsic function names

C.3

Section

subprograms.

arguments

contains

names

the

and

descriptions of the individual PDP-11 FORTRAN-77 intrinsic functions;
for further information on intrinsic functions, see Chapter 6.
The INTRINSIC statement has the

form:

INTRINSIC v[,v]...

The symbolic name of an intrinsic function.

symbolic

The INTRINSIC statement declares

actual argument to a subprogram,

which

reference or

symbolic

This

procedure.

intrinsic

CALL statement.

name

can

the

name

wuse

An example of the use of the INTRINSIC statement follows:
Main

EXTERNAL

Program

CTN

INTRINSIC SIN,

COS

CALL TRIG

(ANGLE,

SIN,

SINE)

CALL TRIG

(ANGLE,

COS,

COSINE)

CALL TRIG

(ANGLE,

CTN,

COTANGENT)

Subprograms

SUBROUTINE TRIG

(X,F,Y)

Y=F (X)

RETURN
END

FUNCTION

CTN(X)

CTN=COS (X)/SIN (X)
RETURN

END

5-18

name

function

can then be passed as an

SPECIFICATION STATEMENTS
In this example, when TRIG is called with a second argument of SIN
or
CO0Ss,
the
function
reference
F(X)
references
the
FORTRAN library
functions SIN and COS;
but when TRIG is called with a second argument
of CTN, F(X) references the user function CTN.

DATA
5.10
The

DATA STATEMENT
DATA statement

array elements

The

DATA

assigns

statement

DATA

initial values
program execution.

before

has

the

variables,

arrays,

and

form:

nlist/clist/[[,]lnlist/clist/]...

nlist
A list

of one

or more

names,

character

variable

names,

substring

array names,

names,

Subscript expressions and
expressions
must be integer expressions containing

array

separated

element

commas.

in
substring
references
integer constants.

clist
A

list

constants, separated
by
commas,
to
be
assigned
Clist constants have one of the following forms:

nlist.

val
n

The

val

number

successive

times

is a nonzero,
of an integer
Subscript

the

entities

1in

same

value

the

associated

unsigned integer
constant.

expressions

and

constant

1is

constant

values

may

The

DATA statement

value

symbolic

integer

to
of

name

constant

assigns the constant values in each
«clist
to
the
preceding
nlist.
Values are assigned in the order

the
from

assigned
The

the

expressions.

entities
in
they appear,

nlist.

left

right.

The number of constants must
correspond
entities in the preceding nlist.

exactly

the

number

When an unsubscripted array name appears in a DATA
statement,
values
are
assigned to every element of that array.
The associated constant
list must therefore contain enough values to £ill
the
array.
Array
elements are filled in the order of subscript progression.

both

the

constant value

have
numeric
rules:
e

The
type

data

constant
of

the

types,

value

the
the

variable

clist

converted,
being

and

conversion

the

entity

based

necessary,

initialized.

5-19

in
on

the

nlist

the

following

the

data

SPECIFICATION STATEMENTS

When

variable
assigned

octal

hexadecimal

array

element,

depends

constant
variable

left

can

numeric

the

data

fewer

=zeroes.

stored,

the

Hollerith

1is

assigned

the

component.

than

the

constant

component

constant

1is

truncated

character

(see

constant contains
variable

array

<character

data

2-2).

fewer characters

array

If the constant value

the

of the

extended

constant

numeric

Table

element,

right with spaces.
than can be stored,

both

capacity
the

the

element,

left.

assigned
the

characters that can be assigned depends on the
the

that can be

1If the constant contains more digits than

variable

type

digits

array element,

with

When a

contains

constant

the number of digits

the

than

the

data

Hollerith

the

type

character

capacity

constant

¢to

number

extended

the
the

1If the constant contains
more
characters
the constant is truncated on the right.

in the clist and
type,

the

the entity

conversion

the

based

the

nlist

are

following

rules:

If the constant contains
entity,
the
rightmost
initialized with spaces.

the

entity,
the

contains more

the character constant

constant value

character

these

constant

fewer bytes than the
1length
of
the
character positions of the entity are

data

is numeric

type,

data

bytes

than

1length

the

type

and

the constant and

the

entity

in the

nlist

the entity must conform to

restrictions:

The

character

The

constant

and

entity

must

must
must

have

an
a

length
of one

integer,

value

entity
1is
specified

initialized
with
by
the
constant;

initialized

any

Dummy arguments,
initialized

the

8-bit

the
a

ASCII

range

these

character
character

character.

hexadecimal

through

255.

restrictions,

the

that has the ASCII code
entity,
then,
can
be

code.

virtual arrays,

DATA

octal,

the

When the constant and the entity conform to

the

truncated on the right.

and virtual

statements.

array elements may not be

example

INTEGER

BYTE

A(10)

BELL,TAB,LF,FF,ACHR,ZCHR

DATA A,

BELL,TAB,LF,FF,ACHR,ZCHR /10%*0,7,9,10,12,'A"',1HZ/

the DATA statement assigns

control

<character

assigns values
Some other
following

'A'

and lHZ

examples

all

byte

10 elements of array A,

variables

to ACHR and ZCHR,
the

DATA

STRING

X (5)

COMPLEX

BELL,

DATA X/2*-3.,4.,2*0.37/,2/(1.0,-3.0)/
DATA STRING/'ABCD'/

TAB,

LF,

and

ASCII

FF.

1in

the

respectively.

statement

segment:

CHARACTER*4

REAL

codes

are

included

SPECIFICATION

STATEMENTS

PARAMETER

5.11

PARAMETER STATEMENT

The

PARAMETER

statement

assigns

The

PARAMETER

statement

has

form:

PARAMETER

(p=c[,p=cl...)

name.

symbolic

Any

valid

FORTRAN

Each

name

in
a

the

value

type

determined

type

other

any

Therefore,
unless the

The

You

name,

becomes
equated.

any

wvalid

constant

and

IMPLICIT
name

statement

(for

defined

preceding

example,

to
be
a
constant
is
that determine the data
type

declaration.

in
a PARAMETER statement is interpreted as
statement is
preceded
by
an
appropriate

name

however,

use

a
it

constant
can

REAL*8

constant,

symbolic

name

symbolic

name

can

The

and

form

are

statement

cannot

appear

either

constant.

containing

the

defined

PARAMETER

defined

only

interpretation

different
provided

FORTRAN-77

from

the

earlier

provides

following

PARAMETER

MU=1,
type

MU).
can

appear

once

sequence

INTEGER

BYTS1Z,

REAL*4

REAL*8

DPI

LOGICAL FLAG
CHARACTER*25
PARAMETER

PARAMETER
PARAMETER

part

real

constant

that

within

the

PARAMETER

and

interpretation

the

DIGITAL

FORTRAN-77

demonstrates

and

any

another

imaginary

only

same

versions

defined

form

both

statement:

the

statement

the PARAMETER statement;
see
Appendix
earlier form and interpretation.

The

constant.

name

statement

name
defined
implicit-typing rules

symbolic

unit

PDP-11

which

symbolic

expression.

symbolic
same

program

above

PARAMETER

itself,.

complex
can

the

integer

name

program that an ordinary constant can appear.
The effect
symbolic name defined to be a constant is that of
using the

symbolic
a

constant;

symbolic

place
in
of using a
constant

the

MU=1.23
PARAMETER

declaration
Once

constant,
or

data

FORTRAN

constant,

symbolic

defined

The

the

symbolic

within

it.

statement

PARAMETER
However,

earlier

for

information

the

use

the

form

the

FORTRAN-77

WRDS12Z

LONGNAME

(PI=3.1415927,

unit.

described

the

FORTRAN.

the

Also,

program

part

DPI=3,141592653589793238D0)
(BYTS1Z=2, WRDS1lZ=BYTS1Z/2)
(FLAG=,TRUE.,LNGNAM='A STRING OF 25 CHARACTERS')

SPECIFICATION

STATEMENTS

PROGRAM

PROGRAM STATEMENT

5.12

The PROGRAM statement assigns a symbolic name to a main program unit.
The PRCGGRAM statement has the
PROGRAM

form:

nam

A symbolic

name.

The PROGRAM statement is optional.

1If you use

the main program.

statement

first

1it,

must

the

The symbolic name must not be

not be
It also must
the name of any entity within the main program.
or common block in the same
entry,
the name of any subprogram,

executable program

(see Section

2.1).

BLOCK DATA
5.13

BLOCK DATA STATEMENT

The BLOCK DATA statement begins a special type of program
declares common blocks and defines data in common blocks.
‘The

BLOCK DATA statement has

DATA

[nam]

A symbolic

name.

BLOCK

the

unit

that

form:

nam

You can

use

EQUIVALENCE,

its terminal
unit must be

only

and

type

DATA

declaration,

IMPLICIT,

DIMENSION,

COMMON,

statements between a BLOCK DATA statement and

statement.
The last
an END statement.

statement

in a

A BLOCK DATA program unit must not contain any
and must not have a statement label.

BLOCK

DATA

executable

program

statements

If you initialize any entity in a common block
declared
in
a
BLOCK
complete set of data-type
a
provide
you must
unit,
DATA program
even
block,
the
in
entities
the
specification statements for all

though

some

the entities are not assigned an initial value.

can use the same BLOCK DATA program unit to define initial values
more

than one common block.

You
for

SPECIFICATION

example

BLOCK

DATA

INTEGER

LOGICAL
DOUBLE

DATA

program

unit

STATEMENTS

follows:

BLKDAT

S,X

T,W
PRECISION

DIMENSION

R(3)

COMMON

DATA

/AREA1l/R,S,T,U/AREA2/W,X,Y
R/1.0,2*2.0/,T/.FALSE./,U/0.214537D-7/,W/.TRUE./,Y/3.5/

END

In
or

this

example,

implicitly

AREAl

and

AREA2.

enough
the
Not

information

data
all

type
the

provided

every

variables

variable
appear

declare
in
the

the

explicitly

common

DATA

blocks

statement.

CHAPTER

SUBPROGRAMS

subprogram

computing
statement.
same

is
This

program

There

are

two

many

cases,

Section

6.1

group

invoked

that

with

can be located
in a different

subprograms:

statements

statement

subprogram

defines
a
referencing

either
program

in
the
unit.

user written and system supplied.
of statement functions, functions,

consist

subprograms

consist

intrinsic

functions.

program

referencing

arguments,
The

subprogram

system-supplied

that

subprogram

receive

these

describes
user-written

system-supplied

6.1

the

generic

called
actual
computations.

describes

subprograms

and

arguments,

kinds

subroutines;

functions
In

statement
referencing

unit

User-written
and

procedure.

subprogram

specifies

actual

for

passes

entities,

use

values,

making

called

dummy

arguments.

actual
and
dummy
arguments;
subprograms;
and
Section

Section
6.2
6.3
describes

subprograms.

SUBPROGRAM ARGUMENTS

subprogram argument is an entity that passes a value to
or
from
a
subprogram,
There
are
two
kinds
of arguments:
actual and dummy.
Actual arguments
are
specified
in
the
statement
referencing
the

subprogram.

subprogram

Dummy

and,

associated
argument

turn,

with

takes

any

assigned

value

returned

when

the

actual and dummy
association from

arguments

are

control

transferred

actual
the

specified

arguments

one-to-one

value

the

corresponding

assigned

the

dummy

corresponding
main

program

arguments ends:
one reference of

the

definition

basis.

Each

argument.

When

subprogram,

there is no
a subprogram

the

Rules

Actual

arguments

array

elements,

must
with
Dummy

agree
which

Governing

constants,

substrings,

are

arrays,

dummy

control

retention
of
to the next.

in
is

argument

is
an
I, L is

Subprogram Arguments

in order, number, and
they are associated.

arguments

variables

can

the

are

association

If (I,J3(3),4) is
a
1list
of
actual
arguments
and
(K,L,M)
associated
1list
of
dummy
arguments,
K
1is associated with
associated with J(3), and M is assigned a value of 4.

6.1.1

subprogram,

actual argument;
argument in the subprogram

actual
from

the

symbolic

with

variables,
subprogram

data

names

type

6-1

with

that

subprograms

expressions,
arrays,
Actual arguments
the
dummy
arguments

names.

become

defined

associated

declared

with

other

SUBPROGRAMS

program units;

subprograms.

associated

with

they are not

dummy

actual

Although dummy arguments

each

dummy

argument

the

name,

actual

argument

may

variables

1is undefined

are

not

variables,

arrays

it is not currently

arrays,

declared as though

constant,

subprograms,

it were a variable,
declared

expression,

virtual array element reference,
not

Each dummy argument name is
associated actual argument.

argument

themselves

argument.

may

array, or subprogram.
the attributes of its

argument

have

subprogram

the corresponding dummy

modified.

A dummy argument declared to be an array can be associated
only
with
an
actual argument that is an array or array element of the same data
type.

the

must not be
equal

actual

argument

array,

the

dummy

larger than the actual argument array;

smaller

than

the

number

element of

argument

that is,

elements

array

it can be

the

actual

argument.

actual

succeeding

argument

elements

corresponding

array,

this

element

and

of the array are associated with elements of the

dummy argument

array.

The

number

actual

argument

array
elements
associated
depends on the size of the dummy argument
array.
The dummy argument array must not be larger than the number of
elements in the actual argument array involved in the reference;
that
is, it can be equal to or smaller than the number of elements
in
the
actual

argument.

valid

Invalid

PROGRAM MAIN
DIMENSION A(10),

CALL
END

X (A,

PROGRAM MAIN
DIMENSION A(10),

B(5,5)

B(1,21))

SUBROUTINE

CALL
EMD

X (Y,2)

DIMENSION Y (10),
END

X(A,B(1,21))

SUBROUTINE

Z(5,2)

B(5,5)

X (C,D)

DIMENSION C(12)

DIMENSION

(dummy array must
larger than

D (5,5)

not be
actual

array)

(dummy

array

not

larger than
of elements

number
of actual
included)

adjustable

subprogram,
the

array

Adjustable Arrays

6.1.2
An

must

dimensions

program.

array

whose
of

1is

dummy

argument

dimensions can be changed,
associated

actual

argument

array,

declared

"adjusted,"

array

to match

referencing

The dimension declaration of a dummy argument array contains

one

Section 6.1.3

integer

for

variables

The

following

rules govern

and,

information on
the

use

adjustable

array must

adjustable

array must

argument

that

optionally,

the

use of

adjustable
dummy

become

array.

6-2

asterisk.

the asterisk.)

(See

arrays:

argument.

associated

with

actual

SUBPROGRAMS

The

size

the

size

Variables

arguments,

defined

adjustable
the

defined;

you

Variables

through

values

integer

examples

PROGRAM

assign

adjustable

assigned

converted

adjustable

can

arguments

following

array

actual

array

values

data

demonstrate

these

blocks.

array

declarator

type

the

than

dummy

must

have

must

become

variables

through

may

integer

data

before

use.

use

adjustable

equal

must

declarator

other

arguments

common

than

declarator

corresponding

value.

type;

The

an
and

Variables
dummy

adjustable array must be less
corresponding actual array.

any

data

type

are

arrays:

MAIN

DIMENSION

Al(10,35),

SUM1

SUM(A1,10,35)

SUM2

SUM(A2,3,56)

SUM3

SUM(A1,10,10)

A2(3,56)

END

FUNCTION

SUM(A,M,N)

DIMENSION

SUM

DO
DO

10
10

SUM

FUNCTION

A(M,N)

0.0

J
I

SUM

=
=

1,N
1,M

SUM

A(I,J)

RETURN

the

example,

The

and

For

information

and

that

statement

lower-bound

These

if the values
changed.
For

values

A(M,?*)

0.0

SUM

I =
SUM

ARRAY

dummy

array

not

and

the

1,N
1,M
+ A(I,J)

can

change

contained

sum

arguments

well

declarators,

values
do

arrays

computes

iteration

of variables
example:

DIMENSION

actual

the

Note

the

Upper-

are

subprogram

A2.

array.

function

control
A.

RETURN
END

END

array.

SUM(A,M,N)

DIMENSION

see

and
N
are
used
specify the size

Section

specified

during

1is
the
adjustable
specified sections

the

2.5.1.

for

subprogram

array

to
of

adjustable

execution,

declaration

even

are

(11,5)

=29

=5
CALL SUB (ARRAY,L,M)

END
SUBROUTINE

SUB(X,I,J)

DIMENSION
J =1
I =2

X (-I/2:1/2,J)

END

In this éxample, the adjustable array X is declared to
the

subsequent

assignments

and J

not

affect

this

X(-4:4,5);

declaration.

SUBPROGRAMS

Note that argument association is not retained
one reference to a subprogram and the next.
REAL

the

interim

between

DIMENSION

B(10)

CALL

S(B,2,3.0)

CALL

Ss1(5,B,3,2)

SUBRROUTINE

DIMENSION
A(I)

S(A,I,Jd)
A(I)

RETURN

ENTRY

(I,A,K,L)

A(I)

this example,
statement

A(I)

RETURN

END

In
the

DIMENSION

The

declared

real

array with

elements

actual

argument

first

reference.

B(10)

statement

sets

CALL

S(B,2,3)

B(2)

CALL

S1(5,B,3,2)

increments

B(5)

which was not

6.1.3

the

retained

Assumed-Size

statement

but

only because

in the

provides

subroutine after

the

Dummy Arrays

An assumed-size dummy array is a dummy array (argument) for which
upper bound of the last dimension is specified as *.
For example:
SUBROUTINE

DIMENSION

SUB(A,N)

A(N,*)

The size of an assumed-size array and the number of elements that
be referenced are determined as follows:
e

the actual

noncharacter
size

the

argument corresponding

array

actual

name,

argument

the dummy array

can
1is

the size of the dummy array is the

array.

If the actual argument corresponding to the dummy argument
is
a noncharacter array element name, with a subscript value of s
in an array of size a, the size of the dummy array is a+l-s.

SUBPROGRAMS

the

array

actual
element

and

begins
character

argument

name,

character

storage

INT(n+1-b)/y,

storage

units,

where

character

unit

the

array

size

length

array.

Because

the

actual

size

array

name

cannot

assumed-size

6.2
A

unit

run-time

key

buffer

array

either

There

three

each
used

are

list

I/0

for

with

the

dummy

array

element

array
any

I/0O

internal

specifier

array

1is
the

not

the

dummy

known,

statement

file
I1/0

I/0

statement

ENCODE/DECODE

operations

types

Table

are

program.

statements

needed
each

Types

statements.

avoiding

statements

user-written

statements
control to

6-1:

FORTRAN

useful

operations

single

type,
the
to transfer

having

two

subprograms.
define

each

duplicate

different

Table
type,

and

6-1

1lists

the

method

type.

User-Written

Subprograms

Control

Transfer

Subprogram

Defining

Statement

Statement-function
definition

Function

reference

FUNCTION

Function

reference

function

Function

following:

is a statement or group of
statements
that
procedure.
A computing procedure can be a series

subprograms

used

name,

subprogram

series

locations

character

substring

SUBPROGRAMS

arithmetic

same

assumed-size

for

specifier

computing

User-written

the

format

specifier

user-written
a

identifier

USER-WRITTEN

performs

name

name,

element

subprogram

Statements

Method

ENTRY

RETURN

Subroutine

subprogram

SUBROUTINE

CALL

statement

ENTRY
RETURN

function reference (Table 6-1)
function
arguments, and is used
is discussed in Section 4.5.

consists
of
a
in an expression.

function

The

CALL

name
and
statement

SUBPROGRAMS

Function and subroutine subprograms can change

the

wvalues

their

arguments, and the calling program can use these changed values.
A subprogram can refer to other subprograms but it cannot, either
directly or indirectly, refer to itself.

Statement Functions

6.2.1

d by a
A statement function is a single-statement computation specifie
in an
name
n
functio
ent
wWhen vyou reference a statem
symbolic name.
|is
name
function
nt
stateme
the
by
defined
expression, the computation
nt
performed and the value produced is used to replace the statemeand
function name in the expression. Statement functions are defined
'

referenced within a single program unit.

A statement function has the form:

([pl,pPl...]1)=e

£
f

The name of a statement function.
P
A dummy

argument.

expression.

The expression (e) is an arithmetic or logical expression that defines
the computation to be performed.

A reference to a statement function has the form:
£

(lal,al...])

The name of the

actual

function.

argument.

on, the
Wwhen a statement function reference appears in an expressiargumen
ts
dummy
the
with
ted
associa
are
ts
values of the actual argumen
in the statement function. The expression in the statement function
is then evaluated, and the result is used to complete the evaluation
of the expression containing the reference.

The following rules govern the use of statement functions:
e

A statement function may not return a value of type CHARACTER.

Statement function

program

names

must

wunique

within

the

same

unit.

A statement function reference must appear in the same program
unit as the statement function.

SUBPROGRAMS

Statement

functions

include

function

(defined

Statement

functions

must

statements

<can

statement

(see

Figure

earlier
be

reference

the

placed

before

data type of a value computed by a
determined
either by the first letter
by a type declaration statement.
Statement

order,

function

number,

dummy

and

Names

statement

arguments

data

type

The

data

type

determined

by
e

type

function

dummy

statement

subroutine.

only

indicate

for

the

statement

arguments

valid

must

Variables

can

unique

arrays

declared

and

function

and

cannot

invalid

used

statement

is
or

serve

statement
function
dummy
arguments
the first letter of the argument name
declaration statement.

‘executable

either

a
Examples

unit).

arguments

only
within
each
statement
function.
having the same names as dummy arguments
used within the same program unit.

all

another

statement
function
of the function name

function.
e

program

1-3).

The

same

functions

EXTERNAL

argument

is
or

are:

valid
VOLUME (RADIUS)

AVG

(A+B+C)/3

(A,B,C)

SINH

(X)

4.189*RADIUS**3

(EXP(X)

EXP

(-X))*0.5

Invalid
AXG(A,B,C,3.)

The

examples

second

valid

(A+B+C)/3

statement

(a constant

function

references

cannot

be
a dummy

argument)

below

refer

the

integer,

but

real)

above.

valid
GRADE
IF

(AVG

AVG

(TEST1,TEST2,XLAB)

(P,D,Q).LT.AVG(X,Y,Z))GO

300

Invalid
FINAL

6.2.2

AVG (TEST3,TEST4,LAB2)

Function

FUNCTION
[typ]

Subprograms

A function subprogram consists of a
series
of
statements
that
make
invoked with a function reference.

The

(LAB2

statement

FUNCTION

has

the

FUNCTION statement followed
up
a
computing procedure.

following

nam{*m
[ ([{p[,p]..-1)]
j|

form:

by
It

a
is

SUBPROGRAMS

typ
Any

data

type

specifier

The

name

function.

except

CHARACTER

(see

Table

2-2).

nam

A data

type

dummy

length

specifier

(see

Table

2-2).

argument.

The function reference
that
1invokes,
function subprogram has the form:
nam

([a[,a)...])

The

symbolic

transfers

control

¢to,

control

nam

When

actual

function

transferred

arguments

(if

name

the

function.

argument.

reference

expression

the referenced

any)

the

subprogram and

function

reference

executed,

the values of

are

associated

the actual
with

the

dummy
arguments
in
the
FUNCTION
statement of the subprogram.
The
statements in the subprogram are then executed and a computed value is
assigned
to
the
function
name
(as
if this name were a variable).
Finally,

returned

RETURN

RETURN statement
acts

function name
containing

The

executed

implied

RETURN.)

the calling program unit.
an

the

function and

control

The

value

assigned

in place
to

the

is now used to complete the evaluation of the expression

the

following

(An END statement used

name.

rules

govern

function may not

the

use

return

A FUNCTION statement must

function

value

the

first

subprograms:

type

CHARACTER.

statement of

function

subprogram.

A FUNCTION

subprogram

must

SUBROUTINE,

BLOCK DATA,

not

statement

label.

contain

the

following

FUNCTION.

A function subprogram can reference another subprogram,
reference

The data

itself,

either directly or

type of a function name can be

FUNCTION statement or

A function name must have
as

function

the

not have

statements:

cannot

statement must

referencing

type

and

specified

declaration

the same data

program,

vice

type

but

indirectly.

either

statement.

subprogram

versa.

ENTRY statements can be included in a function
subprogram
to
provide
one or more other entry points to the subprogram (see
Section

6.2.4).

SUBPROGRAMS

example

function

FUNCTION

X
2

the

function

ROOT:

ROOT (A)

=1.0

EXP (X)

EMINX
ROOT

IF
X

subprogram

=
=

1./EX
((EX+EMINX)*,.5+COS(X)-A)/((EX

(ABS (X-ROOT).LT.1E-6)
=

EMINX)*.5-SIN
(X))

RETURN

ROOT

this

END

The

function

obtain
F(X)

The value
this root

the
=

example

root

cosh(X)

the

uses

cos(X)

passed

the

following

Newton-Raphson

iteration

method

function:

argument.

The

iteration

formula

for

is:
cosh(Xi)+cos(Xi)-A

Xi+l

sinh(Xi)-sin(Xi)

The calculation is repeated
is less than 1.0E-6.

The

function

uses

(see

Section

6.3).

6.2.3

Subroutine

A subroutine

symbolic
of

The

the

FORTRAN

1in

SUBROUTINE

CALL

statement

SUBROUTINE

the

difference

library

functions

between

EXP,

SIN,

and

COS,

Xi+l

and

ABS

Subprograms

subprogram

name

until

nam

computing

procedure

statement.

A subroutine

followed

has

the

series

referenced

subprogram

consists

statements.

form:

[([(pl,P}...1)]

nam

The

name

dummy

You must

use

arguments

CALL

and

unit.,

When control

the

subroutine.

argument.

subprogram,
program

statement

RETURN

Section

4.5

transferred

(if

any)

transfer

statement
describes

the

return

value

implied

the

RETURN.)

the

control

the

CALL

subroutine

calling

the values of

the

actual

statement.

statement

are

associated

with

in
the
SUBROUTINE
statement.
The
are
then
executed
until
a
RETURN
calling program.
(An
END
statement

Unlike

referencing

control

return

subroutine,
CALL

corresponding
dummy
arguments
statements
1in
the
subprogram
statement returns control to the
acts

function,

program.

subroutine

does

not

SUBPROGRAMS

The

following

rules govern

the

use

of subroutine

The SUBROUTINE statement must be

the

subprograms:

first

statement

subroutine.

A subroutine subprogram must not contain
DATA, or another SUBROUTINE statement.

A subroutine

it cannot reference

itself,

ENTRY statements can

provide

edge.

the

polyhedron,
uses

polyhedron

1is

procedure

for

icosahedron.

another

either directly or

included

the

following

given

computed

subprogram,

example

subroutine

The

GO TO statement

TO statement

«cube,

also

calculating the volume.
the

computes

subprogram to

the

volume

subroutine

determine

octahedron,

transfers

control

the

If the number of faces

displays

error

message

Program

COMMON

NFACES,EDGE, VOLUME

NFACES,EDGE

PLYVOL

TYPE

'VOLUME=',6VOLUME

END

Subroutine
SUBROUTINE
COMMON

PLYVOL

NFACES,EDGE, VOLUME

CUBED = EDGE**3
GoToO (6,6,6,1,6,2,6,3,6,6,6,4,6,6,6,6,6,6,6,5)
,NFACES
GOTO 6
VOLUME

CUBED

0.11785

CUBED

= CUBED

0.47140

= CUBED

7.66312

= CUBED

2.18170

RETURN

VOLUME
RETURN

100

TYPE

100,

NFACES

FORMAT
(' NO REGULAR POLYHEDRON HAS
VOLUME=0.0
RETURN

END

whether

STOP

(see

dodecahedron,

Example:

CALL

but

indirectly.

the number of faces and the length of one

tetrahedron,

4, 6, 8, 12, or 20,
user's terminal.

Main

BLOCK

6.2.4).

subroutine

regular

reference

FUNCTION,

one or more other entry points to the subprogram

Section

The

subprogram can

',I3,

FACES.'/)

the

proper

is not
on

the

SUBPROGRAMS

ENTRY

6.2.4

ENTRY

Statement

The
ENTRY
statement
is
a
nonexecutable
multiple
entry
points
to
a
subprogram.
function or subroutine subprogram after
the

statement.

begins

Execution

with

the

first

1in

statement
It
can
FUNCTION

subprogram containing

executable

statement

that
provides
appear within a
or
SUBROUTINE

ENTRY

following

statement

the

ENTRY

statement.

The

ENTRY

statement

has

the

form:

ENTRY nam

[([p[,pl...]1)]

The

name.

nam

CALL

entry

dummy

argument.

statements

are

used

refer

entry

subprograms;
function
references
within function subprograms.
The

following

Within
type

rules

You

govern

function

declaration

can

then

specify

wuse

the

subprogram,

names

wused

ENTRY

within

refer

subroutine

entry

names

statements:

entry name

can

appear

statement.

entry

use

are

entry

name

entry

actual

EXTERNAL

argument

(but

statement
not

and
dummy

argument)
.

You

must

not

use

subprogram)

that

You

dummy

can

order,
in the

use

subroutine,

You

arguments

executable

follow
in

ENTRY

However,

each

entry

use

must

statements

that

differ

dummy arguments you use
statements in the
same

reference

actual

argument

(in

statement.

function,
1list

that

in order, number, and type with the dummy argument list
corresponding FUNCTION, SUBROUTINE, or ENTRY statement.

statements

A dummy argument

ENTRY

name

number, type, and name from the
FUNCTION, SUBROUTINE, and ENTRY

subprogram.

agrees
in the

precede

statement

must

not

can

that

use

referred

in
an

which
ENTRY

the

only

first

the dummy
statement

the

SUBROUTINE,

argument
within

is
a

executable
FUNCTION,

specified.
loop.

SUBPROGRAMS
6.2.4.1

ENTRY

subprogram

1in

and

all

Function
the

mutually associated;

Subprograms - The

entry names

therefore,

contained

a value assigned

name
in

the

function

subprogram

to any one

name

are

Iis

assigned
to all the names.
However, only names of the same data type
can be mutually defined at any one time, because
conversions
between
data

types

are

not

made.

A referenced entry name must be
transferred back to the calling
Figure

6-1

illustrates

the

use

assigned
program.
of

ENTRY

value

before

statement

1in

control

subprogram that computes the hyperbolic functions sinh, cosh,
of

variable

PROGRAM

MAIN

EXTERNAL

TANH,

SINH,

function

and tanh

COSH

X = 24.0
TANHX

TANH

(X)

SINHX

SINH

(X)

COSHX

COSH

(X)

END

REAL
C
C

FUNCTION

STATEMENT

TANH (X)

FUNCTION

COMPUTE

TWICE

SINH

TWICE

COSH

TSINH(X)

EXP(X)

EXP

(-X)

C
C

STATEMENT

FUNCTION

COMPUTE

C
TCOSH(X)

EXP(X)

COMPUTE

TANH

EXP (-X)

C
C

TANH

TSINH(X)

TCOSH(X)

2.0

RETURN

C
C

COMPUTE

SINH

ENTRY

SINH (X)

SINH

= TSINH(X)

RETURN

COMPUTE

COSH

ENTRY

COSH

COSH (X)

TCOSH(X)

RETURN
END

Figure

6-1:

Multiple

Functions

in a

|is

Function Subprogram

SUBPROGRAMS

6.2.4.2
ENTRY in Subroutine Subprograms - To reference an entry
in
a subroutine, you execute a CALL statement that includes the
point name.
The following example demonstrates the use
of
the

statement

reference

Main

Program

CALL

SUBA(A,B,C)

entry

point
entry
CALL

point:

Subroutine
SUBROUTINE

ENTRY

SUB

(X,Y,Z)

SUBA(Q,R,S)

In this example, the CALL is
subroutine (SUB).
Execution
ENTRY

SUBA

(Q,R,S),

CALL

statement.

6.3

INTRINSIC

FORTRAN

AND OTHER

library

perform

using

the

used

entry
point
with the first

actual

LIBRARY

functions

commonly

to
an
begins

arguments

FORTRAN

references
references
result

R =
the

intrinsic

consist

intrinsic

mathematical

the

reference

3.14159

absolute

and

Appendix

actual

6.3.1

passed

1in

the

are

functions,

computations,

listed

and

provided

character

and

1lexical

Appendix

comparison

Function

to
these
functions
are written in the same way function
to user-defined functions are written.
For example,
as
a

3.14159,

its

functions

(A,B,C)

FUNCTIONS

lexical
comparison
functions.
Character
functions are discussed in Section 6.3.4.

The

(SUBA)
within
the
statement following

gives

ABS

ABS (X-1)

value

the

X-1

result
the

data

calculated

assigned
type

and

the

each

multiplied

the

constant

function

and

that

variable

intrinsic

R.
of

arguments.

Intrinsic

Function

References

Normally, a name in the table of intrinsic function names (Table
C-2)
refers
to
the FORTRAN library function with that name.
However, the
name can refer to a user-defined function under any of
the
following
conditions:
e

The

name

used

different data
e

The

name

the

rules

type

appears

provided

function

from
an

that

reference

shown

EXTERNAL

Section

statement

5.8.

with

the

arguments

table.
in

accordance

with

SUBPROGRAMS

Except

when

they

names
can be

are
used

1local to the program unit that refers to them.
for other purposes in other program units,
In

the

data

IMPLICIT

same

6.3.2
Some

name

change

EXTERNAL

same

implied

functions

type

function

Thus, they
addition,

you

use an

rules.

user-defined

function with

unit.

perform

types.

These

generic,

within

For

intrinsic

not change

data

function and a

program

the

name.

the

example,

A generic

function

The

computation

are

computation

category.

same

functions
to be

1is

generic
function SIN(D) refers to
not to the
real
sine
function.

but

referenced with
reference

performed,

selection

that is, the actual computing procedure
left to the compiler, which
chooses
a
category
on
the
basis
of
the
data
argument.

statement,

function does

the

intrinsic

the

data