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Document:	Programming in C
Order Number:	EY-1925E-H0
Revision:	2
Pages:	134
Original Filename:

OCR Text

PROGRAMMING

Digital

TIN

Equipment

Educational

EY-1925E-HO-0002

Corporation

Services

Second Edition, August 1985

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 in this document.

The software described in this document is furnished under a license and
may be used or copied only in accordance with the terms of such license.

Digital Equipment Corporation assumes no responsibility for the use or reliability.
of its software on equipment that is not supplied by DIGITAL.

Copyright © 1985 Digital Equipment Corporation. All rights reserved.
Portions of this text are based on LEARNING TO PROGRAM IN C, a book

GRAMMING WORKSHOP, written by Thomas Plum, copyright 1983 by Plum
Hall, Inc.

The following are trademarks of Digital Equipment Corporation:
ALL-IN-1

DNC

BAL-8

DNC

CDP

EduSystem

PRO/NAPLPS
PRO/RMS

- PRO/Videotex

COMPUTER LAB

FLIP CHIP

PROSE

COMSYST

FOCAL

COMTEX

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QUICKPOINT
RAD-8

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SABR

DECmate

MASSBUS

Tool Kit

DECnet

OMNIBUS

TYPESET-8

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DECwriter

Professional

PRO/BASIC

VAX VTX

PRO/FMS

Programming

~outline-

page

Programming in C

Course

TEXT:

"Learning

Program

by Thomas

Qutline

Plum,

Plum Hall

Inc.

Monday:

Introduction

C
C

Operands and
Control Flow

Operators
- if, else

Control

if,

switch,

while,

for

Tuesday:
Flow

comma,

do while,

break,

goto

C Functions
The

Preprocessor

Wednesday:

Pointers

The

and Arrays

Library

and

including array arguments

including

sprintf

and

sscanf

Thursday:
Structures

and Unions

and

including pointers

structures

The

Library

File

I/0

Pointers

and Arrays

pointer

Pointers and Arrays
functions

cmd

arrays

Friday:

The

Library

Structures

system

and Unions

level
-

line
I/0,

arrays

args,
heap

pointers

allocation

structures,

unions

Programming in C

-outline-

page 2

TEXT ASSIGNMENTS

It is recommended that the following reading in the text
"Learning to Program in C" be performed and the questions
Programming exercises are provided
in that reading answered.
at the end of this workbook as a replacement for those in
the

text.

Monday
:

Optional assignment - computer concepts (as needed)
- Chs. 1, 2.1
"Learning to Program in C"
"Learning to Program in C"
2.6,
3.4,

2.7,
3.5,

"Learning to Program

in C"

Sections
Sections

2.8
3.6

Tuesday:

Sections
Sections

3.8,
5.4,

3.9,
5.7

to Program

in C"

3.11

Wednesday:

"Learning

Section
Sections

3.12
7.2,

7.4

Thursday:

"Learning

to Program

Sections
Sections

Friday:

(or

following

"Learning

the

7.3,
8.1,

7.7
8.2,

8.6

completion

to Program

Ch.

in C"

"Programming in C Workbook"
Ch. 9

the

course)

Programming

prage

~outline-

in C

TABLE OF CONTENTS

intro

Y
C&: s & & ® ® @& ® & © 2 & ®© © » B L o & € & H © e 6 & @ & @ © 8 v O &
mat 18
W}l’y C s ® & ©® © © ® ©° B & & & & 5 & S @ S & o B S & & @ ¢ & & & 5 © ¢ o 6 e ©& 8 O
A quick overview.....
Identifiers, keywords, comments, constants.
®

Data

Lypes. .o

®©

i it ottt ecessooscsososse

Compile and execute a simple C progranm.
A program to copy input to output......
A program to count lines, word, chars.
Sample formats for printf.............

input.......

[

12
14

Buffering of

16
17

operands
Data

18
19

types....ceveenen

Constants.............

String

Relational

operators..

Expressions,
Logical
Type

constants......

Declarations..........
Arithmetic operators..

[ 4

operators,

[

[ 3

and operands

operators......c.cceeieeveeesen

ConversionsS. ...c.oceeeeessecees

Type conversion examples and cast.
Lvalue and rvalue......ceeeoeeessase
increment and decrement operators.

21
22
23
24

27
28
.4

Arr Ay S. it ieeessosoaossssonsssssess
Arrays of characters............

30
31

The array indexing formula......
String functions.....cceceeveeee
Bitwise operators. ...ccev v vvesss
Bitwise "right rotate" function.
Assignment operators.......cec..
Operator precedence......ccesooesseee
The conditional operator (thenelse)

L 4

33
34

36
37
38
40

3 -

Programming

-outline-

page

TABLE OF CONTENTS (continued)

control
Statements

(else)

Else

Switch

and

blocks..

statement......
statement.......

While

and

Comma

operator.........

Do while

for

statement....

42
43
44

statements.

statement.....

Break and continue.....
Goto statement.........

48
49

functions
What

function@?....

Basic function syntax..
Non-integer functions..
Argument

passing.......

Recursive

functions....

[

50
51
52

[

Initializing automatic scalars.
Storage class....cco...

56
57

Static storage class...
Initializing arravs....
External variables.....

60
61

storage

class.

-4

]

-4

L 2

ocope rules.....c.coc00
0
Initialization summary.....

63
o4

Empty brackets: three cases
Passes of C compiler.......

preprocessor

DefineabfifiQDQQQOD&Ofiflfiw
Define and macros......

67
68

IncludQDODfibebeofibfiblbb

Conditional compilation.
Llneoeoo»»ooaflnosoocpeoo

Programming in C

page

-outline-

TABLE OF CONTENTS

(continued)

pointers

What is a pointer?......cccvievenns
Declaring and using pointers..........
Simple examples using pointers........
Pointers as function arguments: swap..

Pointers as function arguments:
Pointers

75
76
o

78
79

scanf.

and arraysS.
..o ceeeooooncoss

Pointer and array examples:
Array arguments:
Array arguments:

hex.c,

index.c.

strcpy, strncpy........
read.....c.cceescoeoee

Array arguments: write........ccooeeee
Pointer arithmetic........ccict
e csnss

82
84

Multidimensional arrays.....ccceeevesss
Pointer aArrayS...ceceeceoocsccsscsscsees
Command line arguments to C........c.c..
Variable number of function arguments:
Pointers to functions.......oev
v

88
89
91
92

structures
Structure basiCS. .. .vv v veeronsoseas
Members of structures......ccceeceeeoeos
Members and nesting. ......cceoeceeceeceos
Defined types for structures..........
Pointers to structures......ccceeeeonoe
Formats for structure definitions.....
UNions. ¢ v voeeeeeeeeeseoeceoosssssocnsoescs
Typedef ...
ittt neseennsencnnscen
Arrays of structures........ceceeveees
Bit fields....eeeeeteeeeeooeosnsoconos
Linked 1lists.....vcuoceeececcescsssocescs

93
94

95
96
97
99
.100

. 101
.102

.104
.106

Programming

-outline-

TABLE OF CONTENTS

Clibrary
standard

input,

Character

standard

input/output:

output,

(continued)
and

getchar,

page

standard

error..... 108

putchar.........cccece.. 109

Line

input/output: gets, puts........
ittt eecerocconsee 110
output: printf . ...
ie ettt eececoecsenecnnses 111
Formatted input: scanf.....cee
e eeeeescescescooosonsonoes 112

Formatted
1/0

and

from

strings:

sprintf,

sscanf.........cccc... 113

File I/70. ...
et ietieeeooeosoossossonassocssssossecscssss 114
Example of File I/0...
.t eeeeeeoeeesonoseoosocccoocnsnoe 116
Error

output:

System

1evel

perror,

fprintf....

...ttt eecocennn 117

I/0. ...t eeeeeneeeeeoeensosoenonnonsoness 118

Heap

120

allocation:

malloc,

free.......oi
ettt veceeconenees 121

style

Data

and

variables.

. ...

it ittt eneeetnoneensononnnss 122

Operators. ...ceeeen.s s s s s s s e e s s s
Control

structures.......c..

FUNCEIONS.
.t it i i it
Common

€

e s s e e e e e s e e seaeeneesene 123

ittt eeoeeesoeonsannones 124
ittt ittt ittt

DUGS . ottt i et ittt

ct et oneesonsesansononess 125
e enensenscesonesesoneesnos 126

labs

Monday Programming Assignments........oeeeeereenesooncen 128
Tuesday Programming Assignments.......c..eeeeeerceoooooss 129
Wednesday Programming Assignments.........oeeveeeeonsess 130
Thursday Programming AsSsignments.......veeeeeeeeoeonesns 131
Friday Programming Assignments. . ......ooeeeeeeeoncoonones 132

0021

Ox11l

| ————

dc?2

0022

Ox12

dc3

0023

O0x13

dc4
nak

0024
0025

Ox14
Ox15

syn

0026

Ox16

etb

0027

Ox17

can

0030

Ox18

0031

0x19

sub

0032

Oxla

esc

0033

Ox1b

0034

Oxlc

ags

0035
0036

Ox1d
Oxle

0037

Ox1lf

0040
0041

0x20

Ox21

OTADI

0042

Ox22

0043

O0x23

0044

0x24
Ox25

|
| TVGIINS | MO
| SN | MT——— L, | AN
I
MEGITY | WAL | ORI

RN
¥~

| N
ORI, YDA, ST
A
GG ST

0045
0046
0047
0050

0x28

0051
00572

O0x29

Ox26

O0x27

0x2a

54
55

0066

0067

0x36
Ox37

0070

0x38

0071

0x39

00772

Ox3a

59
60

0073

0x3b

0074

Ox3c

0075

Ox3d

62
63
64

0076

Ox3e

0077
0100

Ox3f
0x40

0101

Ox41

0102

Ox42

0103

0x43

0104

Ox44

69
70

0105

0107

0x45
0x46
Ox47

712

0110
0111

0x48
0x49

0106

0112

Ox4da

0113

Ox4b

0114

Ox4c

0115

Ox4d

0lle

Ox4de

0117

Ox4f

0120

0x50

81
82

0121
0122

0x51
0x52

0123

0x53

84
85

0124
0125

0x54
0x55

S<
G
Dled ~ MIN

O~
Wt

0x35

A
-

ToOetne om0

0065

R RWUWHEIDTOHRDDLAO
DD

dcl

TR QTDOITE

Ox0f
0x10

0064

0x33
0x34

0020

| ST

WM
M.

0017

I | TN SR, | SO

si
dle

Ox32

Y S

Ox0e

00672
0063

octal,

0016

50
51
52

page

lid—

0x0d

Ox31

0015

0061

OO0

<moaN | SN —————tws v

0013
0014

0x30

O0x0a
Ox0b
Ox0c

0060

GO mchonts SR

0x09

00172

fimaramn roeboL | SO

0011

Ox2f

DY e

Ox07
0x08

| _————

0007

0010

Ox2d
Ox2e

477

0055
0056
0057

bel_

45
46

i wEROSTTD |

0x06

Ox2c

0006

Ox2b

0054

ot Samdvmen. GRS WRESES RGN WIS

Ox04
0x05

0053

| acOROMED eavicim | SCRGINE OCRNEWS

0004
0005

eot
eng

decimal,

SGOMEEAR SRS AN

O0x02
O0x03

ASCII,

SR, | COMSUIN | SHOINON | BT

O0x01

ST SO

Ox00

Ty e

- O

0000

0001
0002
0003

ack

-outline-

characters:

At ormery oarnin ww o

ASCTI

stx
etx

IO U

oo
wowomi

soh

ctmire | o

nul

somm—

Table

NIy

Programming

del

hexadecimal

0126

0x56

0127

Ox57

88
89

0x58
0x59

0130
0131
01372

0133

0x5b

0134

O0x5c¢

Oxba

0135

0x5d

Oxbe

0136
0137

0140

Ox60

Ox61
0x62

Ox5f

0141
01472

0143

0x63

100

0144

Ox64
0x65

101

0145

102

0146

103

0147

0x66
Ox67

104

0150

Ox68

105

0151
0152
0153

Oxba
0x6b

106
107

0x69

108

0154

Ox6bcC

109

0155

Ox6d

110

0156

Oxb6e

111

0157

Ox6f

112
113

0160
Olel

O0x70
Ox71

114

0162

115
116

0163
0164

0x72
Ox73
Ox74

117

0165

0x75

118

0166

119

0le7

O0x76
Ox77

120

0170

O0x78

121
122

0171

0x79

0172

Ox7a

123

0173

0x7b

124
125

0174
0175

Ox7c
Ox7d

126

0176

Ox7e

127

0177

Ox7f

Programming

-intro-

A general

purpose

Low

level

"portable

Can

access

storage

Weak
No

programming

many

I/0

Cannot

language.

assembler"
computer

allocation

typing

page

objects

directly.

heap mechanism.

rules.

facilities.

access

composite

Single

thread

control

Minimal

run

Modern machines:

time

Byte

flow

environment

addressing

Address
Stack

objects

similar
cheap

integer

a whole.

-intro-

Programming

Efficient

code

a variety

generation

modern machines.

UNIX consists of 12,000
of C and 800 lines of
assembler language.

on a variety

machines.

Portable
Both the compiler and the
library are easily ported
to

lines

Easy

other

learn

machines.

and

use.

page

Programming

-intro-

page

A guick overview

Fundamental

data

characters,

types:

integers,

Composite data types:
pointers, arrays,

and floatings.

structures,

unions,

functions.

Flow

control:

if,

Recursion

while,

and

switch.

'for

function

global

within

file,

global

free’:

storage.

data:

internal

do,

reentrancy

automatic

ocope

for,

through all files.

Weakly typed:
many data

permitted.

conversions

block,

Identifiers,

-intro-

Programming in C
kevwords,

comments,

page 11

constants

Identifiers are strings of letters

beginning with letter.
and digits,
Upper and lower case are distinct.

(including underscore)

Variables must be declared before use.

First eight characters are significant
(less for externals)

Names that start with underscore should be
reserved for

Keywords

system programs

(reserved):

auto
|
break
case
char
continue
default
do

Comments
between

double
else
entry
extern
float
for
goto

Constants:

Separators:

;{1

and

3.07

"'x '’

(

)

Whitespace:

blank or newline or horizontal tab,
(Whitesmiths: any other non-printing character.)

static
struct
switch
typedef
union
unsigned
while

consist of any text
/*

if
int
long
- register
return
short
sizeof

Suggestion:

80-character

line

limit.

“help"

Programming

-intro-

Data

Bytes

page

types

Type

Description

char

single

byte.

short

integer.

int

integer

(same

size as
integer.

long

float

single

precision

floating point
double

pointer).

number.

a double precision
|
floating point number.

Programming

Compile

-intro-

and execute

page

simple C program

main()

{
printf("this

3
To run using the
O
EDITING
S

program.\n");

UNIX operating

svstem:

myprog.c

i{new text)>ESC

insert

a{new

new text

(before

append

new text

(after

e
W .

text>ESC

move

cursor)
cursor)

cursor

left

one

column

one

line

move

cursor

down

move

cursor

move

cursor

right

one

line

one

column

"gobble" character under cursor
write output file and quit

s Wq

COMPILING & LINKING
$

-0 Myprog myprog.c

RUNNING PROGRAM

$ myprog
run using the VMS
EDITING

operating

system:

EDIT MYPROG.C

AC
arrow keys

delete

key
key
(CTRL-Z>EX

PF2

to enter character mode
to move cursor on screen
to delete
to get

characters

help

exit

on
editor

using

keypad

COMPILING
$

CC/LIST MYPROG

PRINT MYPROG

listing file
object

file

to get

hard

MYPROG.LIS
MYPROG.OBJ

copy

listing

LINKING
$
$

ASSIGN SYSSLIBRARY:CRTLIB.OLB
LNKSLIBRARY
ASSIGN SYSSLIBRARY:VAXCRTL.OLB LNKSLIBRARY

LINK MYPROG

RUNNING PROGRAM

RUN MYPROG

image

file

MYPROG.EXE

V1.0
V2.0

file

FProgramming in C

-intro-

A program to copy

copy

input to output

{(stdio.h>

#include

page 14

input

output

main()

{
char

c¢;

getchar();

while

EOF)

{
putchar(c);

getchar();

}

exit (0);

/*exit (1) in VAX-11C*/

At the

top of each

#include

source

file

that

performs 1/0

{(stdio.h>

defines:

EOF

-1

getchar
()

putcha()
r

Programming

in C

-intro-

A program to count

#include

<{(stdio.h>

lines,

count

words,

lines,

chars

- page

words,

chars

input

* /

main()

{

int inword;
short nc;
short nl;
short nw;
char c¢;
inword
nc

while

/*
/*
/*
/*

currently in a word?
number of chars
*/
number of lines */
number of words */

/* most

recently

read:

char or EOF */

NO;
=

((c

getchar())

EOF)

{
++nc;

(¢

'"\n’)
++nl;

(¢

==
" "
inword

|| ¢ ==
= NO;

"\n'

else if (inword == NO)
{
inword
= YES;

++nw;

3
}
printf("%d

exit
3

(0);
|

%d\n",

nl,

/*exit(l)

nw,

nc);

1in VAX-11C+*/

"\t")

Programming

-intro-

Sample

Integer

formats

for

page

printf

tyvpes

integer

hex

octal

%030

3-digit

ASCII

(printed decimal,

signed)

integer

octal

integer with

0-fill

character

otrings of characters

ASCII

character

%.5s

A maximum

string

(null-terminated)

5 ASCII

characters

from a

string

fixed-point,

8 wide,

-2345.78

Floating point

%8.2f

%12.5e

e-format:

-2.45678e-12

places:

page 17

~intro-

Programming in C

Buffering of

input

On most systems, input from terminals is buffered one line
This allows correction of typing mistakes on
at a time.
that

line.

one

Thus, the program does not see the input until the newline
(Each operating system has its own method of
is typed.
over-riding this buffering to allow a program to see each
character as

typed.)

EXAMPLE

<{(stdio.h>

#include
/*

copy

input

output

main()

{
char

c¢;

c = getchar();
while (¢ != EOF)

{
putchar(c);

getchar();

}
3

THIS WILL HAPPEN
S

program

dog and cat
dog and

cat

THIS WILL NOT HAPPEN
|

program

ddoogg

aanndd

ccaatt

Programming

-operands-

Data

The

fundamental
char
short

page

types

data

types

:
:

a
a

byte.
'short’
'long’

are:

integer

long

float

single-precision.

integer

double

int

bits
bits

bits

double-precision.

bits

pointer

8
16

(address)

Signed/Unsigned

short
unsigned

short

range

values

range

values

unsigned

long

unsigned

int

num;
ab;

unsigned

char

Defined

data

types

#define

tiny

-32768
0

+32767

65535

char

unsigned

tiny

vy;

#define

ushort

#define

bool

Advantages

unsigned

short

int

defined

data

types:

semantic

distinctions

portable

data

(different

different
enhance

readability

defines

hardware)

bits

Programming in C

-operands-

page 19

Constants
O

Character

one

constants:

char within single quotes
le'

f\tl’

I\nf’

I\lOl

Integer constants:
decimal:

142,

octal:

17,

|
34721

a leading zero indicates an octal
042,

hexadecimal:

Oxo6f,

01,

0732

constant,

a leading 0x indicates hex constant,
0x238,

0xl1l7

integer constants are represented in int
(on PDP -

200000L

1is

(2/4 bytes)

long constant)

Floating constants:
1.23
.23

1.00
17e~-23

floating constants are

represented in double

(8B bytes)

Programming

in C

-operands-

page

String constants

String

constants:

characters

"Hi

Stored

By convention,
is

written within double

there"

the

in memory as

null

the

array

last

character,

chars.

character of a string
‘'\0’.

QUESTIONS:
0

What

the

Hhelloll

quotes:

What

size

the

these

two

difference

between

strings?

page 21

-operands -

Programming in C

Declarations

)

Variables must be declared before use.

Declarations specify a type, followed
by a list

things having that

short a,

char gq,

type:

sC1001;

The most readable format is an alphabetized list,
one variable per

short

line,

with a comment:

/* buffer index counter #*/

int more;

/* is there more data? * /

char tbufl801;

/* terminal I/0 buffer */

double x;

the unknown A/

Programming

~operands-

Arithmetic

operators

(remainder)

% gives

remainder;

gives

page

the

% b

remainder

dividing a by b.

Not valid for double, float.
* and / and %
have higher precedence
+

and

Unary

has higher
any of the

precedence

funca()
call

than

above.

No guarantee

could

than

a(),

evaluation

funcb()

b(),

(y+z)

(x+y)

(y*z)

(x*y)

L
-

L
ad

sequence:

funcc()

c()

first.

(X + z) +y

Compiler can rearrange across these parentheses.
Parentheses are not adequate for specifying the
Allows optimization:
order of calculation.
(x

Value

of:

Dbecomes

-5

Programming

in C

-operands-

Relational

The

relational
>

lower

(is

Assignment
(and

not

are

result

operator

lower

(not equal)

(0=FALSE,

still

precendence

Previously we

1=TRUE)

lower

precedence

than

operators.
+

wrote:

while

((c

while

(¢

getchar())

EOF)

not:

Always

QUESTIONS:

(assignment)

arithmetic

why

are:

equal)

relational):
=

All

are:

precedence

produce

operators

(

page

getchar()

parenthesize

What

embedded

the

value

)

of:

EOF)

assignments.

Programming

in C

-operands-

Expressions,

Operators:

Operands

operators,

Expression
operand

upon):

1234

‘x’

OxFF

(examples):

operator

unary-operator

operands

(the data being operated

constant
variable

and

page

operand

-40

constant

variable

‘0

Subexpression

expression

that

operator

operand

expression

y+2

x=(y+2)*46

subexpression

v+2

larger

expression

part

Programming in C

~pperands-

Logical

logical

means
means

operators

(and)

||
I

(or) (pipe
(negation)

Precedence of
Both have

€

||.

than relational

operators:

(zero)

into YES

(one).

MAX &&

((c=getchar())

'\n’))

Sequence guarantees
in C:

full-expr

"Short-circuit": qguarantee left-right sequence,
stop evaluating when result is determined:
if

than that

Negation is monadic (unary): takes one operand.
Converts YES (non-zero) into NO (zero),
NO

characters)
(exclamation point)

&& greater

NO (FALSE)
YES (TRUE)

are

lower precedence

operators

"semi-Boolean":
Zero
non-zero

The

page 25

| ]

(more

Truth Table

ARG

OESEY

STNSD

MWD GKEN GLGR

WSS

WMRW

Sher wC

GRS

to come...)

Programming

-operands-

Tvpe

Widening

conversions

operands

Operands

page

"int"

("coercion"):

sizes:

2-byte (16 bit):

PDP-11, 8080, %80,

4-byte

68000,

(32

shorter

bit):

than

int

are

loaded

VAX,

into

...

int-sized

temporaries.
long

remains

float

Type

operands

coercion,

the

other,

unsigned

are

loaded

one

operand

temporaries.

unsigned

long

unsigned

operand

"slightly wider"

1int,

unsigned

double
float

unsigned

short

short
char

char

int,

than

equal

than

size.

signed.

machine

unsigned

widened

4-byte

long
int,

smaller

further

double

machine

means

double

float

into

balancing:
After

2-byte

long-size.

int,

unsigned

long

unsigned

short

short
unsigned

char

preferred

type

for

this

machine

architecture.

long

Programming

in C

-operands-

Type

conversion

For

assignments,

converted

examples

the

and

right

type

page

cast

side

Value

the

left

side.

short 1i;
tiny t;
float

Types

i=¢t;

is sign

=1;

gets

=1i;

converted

truncated

coerced

using a

can be

extended

low-order

byte

cast.

short i;
double
d

From Standard

sqrt((double)

library:

sqrt()

#*/

i);

float

Programming

in C

-operands-

Lvalue

lvalue has:
type, storage

A simple

case

|
class,

lvalue

name,

is an

location.

identifier.

'Right hand side of an assignment may be any
object that has
an rvalue if it

rvalue

Left side of an assignment is an object with
a location in storage. This object is called
an lvalue.
An

and

page

a value. This object
is not an 1lvalue.

rvalue has:
type, name,
simple

case

rvalue

constant.

simply fetches

¥;

Which of

]

QUESTIONS :

called

value.

Making a value from an lvalue
its value from its location.

legal

illegal

the

*/
*/

following are

lvalues?

page 29

-operands -

Programming in C

increment and decrement operators

adds one to a variable (lvalue).

++ or -- used before the name

subtracts one from a variable.

-—

(prefix):

= a;
..
e..++b.

value of expression is a + 1
++

used after

the name

(postfix):

b = a;
@ @ 0b++0 & &

value

Fill

expression

in the missing parts:
short

X++;

++x;

_*/

++,

--.

Do not

rely on exact

sCi++1
sCi++1
sCil

=
=
=

time

It will be done by the next sequence-guarantee point.
tLj++1;
tCLid;
tLi++];

/* GOOD */
/* BAD
4/
/* BAD
4/

Simpler rule: if you increment or decrement a variable,
do not refer to it again in that statement.

Programming

in C

~operands-

page

Arravs

composite

The

data

declaration:
short

declares

type

scoresC3071;

that

scores

A declaration
char

msgl801];

name

is:

msqg

type

is:

char(801]

"sandwich"

short

integers.

type

+ name.

Arrays are subscripted starting at zero
(just like birthdays and anniversaries!)

initialize
for

The

an array

contains a

scoresl0l1,

(i=0

for

scoresCl],

the array

; i{(30 ;
scoresli]

...

scores([29]

scores

zero:

++i)
= 0;

statement‘used above:

init:

i=0

done

test:

i(30

body:

scoreslil

step:

++1

prepare

scoreslLil]

is an

lvalue.

once

YES,

before

loop

body and

step

0;
for

test

Programming in C

-operands-

Arrays

page

of characters

Strings are

By convention,
the null character, '\0’, whose value
|
zero,
1s put on the end of all strings.
This
eliminates the need to store string lengths.

For

the

Ial’

represented

string

Ipl'

"april",

Irl'

Iil'

Programs which build
‘A0’

those

the

lll’

I\OI

arrays

compliler

strings must append

strings.

characters.

generates:

Programming

|
|
CLEE

in C

The array

indexing formula

char sC5121;

“type"

|
|
EETD

sC0J

Basic

EAD

AEDO

~operands-

|
|
Aes

CORE

GES

WOED

sCll

THITD

l
l
QRSO

OBMD

GNP

'page

eAIe

sC2]

is:

char[512]

s[5111

indexing formula:

address of jth element =
address
J

(size

zero-th element
of

each element)

QUESTIONS:

Suppose

&sLC01

What

Suppose a
short
and

2000

(monadic

&sC10137?

declared:

al5121;

&al01

4000

What

&alC10137?

"&"

means

address-of )

Programming

in C

-operands-

page

String functions

cpyastr

#include

s2,

3);

| === |

| ===~ l

<{(stdio.h>

/*cpyastr
* /
cpyastr

(sl,

copy a

(sl,

s2,

char slC1];
char s2C1;
unsigned int

string

from

/*destination string*/
/*input string*/
/*number of characters

|
copy*/

{
short

for

(i=0

;

i<n

slCil

Manipulation of
In standard C,

Alternative

for

++1)

s20iJ;

strings must be done explicitly.
no statement will process an aggregate.

to above:

(i=0

slCidl

;

i<=n

'\0‘;

(sllCil

s2Ci])

/Anull body/

'"\N0’

;

++i)

Programming in C

-operands-

Bitwise

bitwise

and

page 34

operators

(bit-and)

& |

...' ___________

()]

bitwise

(bit—or)

......,...! uuuuuuuuuuu

~ |

bitwise exclusive or

...' ...........

Example:

char x

0x16;

x &

OxF

0
0010110
00001111

00010110
0 000O0O0O0O1

What

the difference between && and & 7?

QUESTIONS:

What

are

O0x3F

the

0x67

Ox67

values

the

following

expressions?

Programming

-operands-

in C

Bitwise operators

page 35

(continued)

unary ones complement

QUESTION:

~“0

1is

OxFFFF or

0177777

1is

OxFFFE or

0177776

~ bitwise

left

bitwise

right

007

What

(bit-not)

the

shift

(zero fill)

shift

value

010

16 bit

(signed fill)

of:

machine

Programming

in C

-operands-

Bitwise

Right

rotate

"right

rotate"

bits

function

shifted off

rolled

Example

using

8 bits:

right

rotate

into

page

the

right

are

to be

left

function

short

rightrot

(n,

short n;

short

16 bit word to

rotate

number

b>0

; --b)
.
01)

b;
{

for

bits

(
{
if

;

(n &

(((unsigned)n

((unsigned)n

repeat

else
»>>

1);

3
return

(n);

Always parenthesize bitwise expressions;
bitwise

precedence

tricky.

rotate

times

#*/

0100000);

Programming

in C

~operands-

Assignment

Expressions
X

of
X

can be written
X

in the

compressed form;

X *=

/* multiply x times

/=y

subtract

from x */
z

/* x gets divided by

*/
(y

+ n;

operators:
+

form;

X -=

operators
-

the
+

page

A&/

Usefulness:

all00
can be

afl00

§1

written:

all00

all0o0 *~ i +'j] is evaluated only oncel
0

The

form +=

is preferred to the

consider

#define

tiny

form

x=-1;

char

tiny x, y:
X

Expression result
converted to type

not widened

int

#*/

is value from operation,
of left-hand side.

Programming

in C

-operands-

Operator

precedence

a+ Db

Which binds

tightly,

By historical agreement,

Fully parenthsized:

Or,

in words,

a +

"multiply b

QUESTION:
Put

into words

+ b)

+ d

the

#*7?

then add a"”

the *

times

page

Programming in C

-operands-

page 39

Table of precedence

Precedence
Level

Operators

()

’

.
--

(type)

(etc.,

op=)

|I=

=-=

x..

show the binding:

Parenthesize

QUESTIONS:

€31

Programming

The

conditional

—-operands-

operator

page

(thenelse)

The

’‘'thenelse’
"7?:" operator
provides a conditional expression

in C.

Ternary

(triadic)

operator:

takes

three operands.

25)
X

z2;

Vy;

else

rewritten:
X

-x

Examples:

absx

- minxy

?2x

:V;

A T ]

Pregramming in C

-control-

Statements

expression

makes

page

and blocks

plus

semi-colon

statement.
++X;

getchar();

X +

Curly braces
denote

{

a block

useless

(compound

{
=

Null
one

statement:
lonely

statementx/

++];
X

but

semicolon

statement)

Programming

in C

-control-

(else)

page 472

statement

(expression)

0
non-0

=)
=>

FALSE
TRUE

statementl
+—

|
|

else
statement?2

|
~+

Statement can be
if

simple

(i<4)
xCil

compound
if

1i;

(1<4)
B!

yCil = 1i;

' xCil = 1i;
yL£il

1i;

The

else

clause is associated
with the closest un-elsed

(bC3jil

bLil

statement.

{

else
printf

("error\n");

(bLjl

bLild

3
else
printf

Always

put braces

around a nested

if.

("error\n");

-control-

Programming in C

page

Else if statement

(exprl)
statementl

else

(expr?2)

statement?
else

(expr3)
statement3

else

~default

statement

Last else

only one statement is executed

QUESTION:

clause

is optional.

What does this program print?
for

++i)

4)
printf ("A");

else

(i % 2 == 0)
printf("“B");

else

(5 < 1)
printf ("C");

1;
{
if

else

printf ("D");

3
putchar(’'\n’);

Programming

-control-

Switch

page

statement

Example:

switch (cmdchar)
{
case

‘a’:

add(nl);
break:
case

‘d’:

delete(nl,

n2);

break;
case

‘c¢c’:

change(nl,

n2);

break:;
default:
remark("?",
break:

""):

Execution
whose

starts at

the

case

label

constant is equal to the
expression, and continues til the

the

Default

You

switch,

should

Prefer

the

end

break.

optional.

always

switch after

each

escape

case

the

with a break.

switch to elseif unless different

conditions
sequence.

are

tested

tests

must

Programming in C

-control-

statements

while and for

while

page 45

(expr)
statement

test

is at

top of

the

loop

for (exprl; expri; eXpr3)
statement
same

expr 1;
while (expr2)
{
statement
expr 3;

Use for rather than

while

when:

loop to be performed a known number of times
is

there

"Endless"

loop

#define

FOREVER

loop initialization

FOREVER

{
wait

sec

print time
3

for

(;;)

Programming in C

-control-

Comma

j=k,

Complete

left

list

page 46

operator

num=1i++,

Evaluated

ct=1++;

right.

sequence-guarantee

full-expression

| |

’

Function to reverse a string in place
("SPOON"

int

reverse

char

sLC1;

becomes

"NOOPS")

(s)

{
char t:;
short i,

for

7J;

(i=0,

sCild,

strlen

(s)

sCild

sCj1

;

i<(j
,

;

sCLjl1

++i,
=

--7)

Programming in C

-control-

Do while

statement

while

(expr);

test

bottom

The do while

the

loop

statement

is desirable only when the
problem dictates that statement
be

executed at

least

once.

{
printf ("Answer
ans

getchar();

while

(getchar()

");

'\n’)

'n’);

3
while

(ans

'y’

&& ans

page

Programming

-control-

Break and

Break causes

from

for,

continue

early

while,

while

do,

exit

switch.

(expr)

{
statement

(expr)

break:
statement

1/2-time

loop

FOREVER

{
statement(s)

(expr)

break;
statement(s)

}

Continue

statement

Continue
of

the

while

causes

for,

the next

while,

do.

(expr)

{
statement

(expr)

continue;
statement

iteration

page

Programming in C

-control-

Goto

goto

label;

page 49

statement

never needed.

label:

for

(...)
for

(f..)
if

(error)
goto

error:

/*code

fix

the

errorx/

error;

Programming

~-functions-

What
e

subl.c

imain()

| subl ()

subl(arg)

eee

sub2(arg)

page

sub2.0

-lc

a function?

pgm. C

...

sub2.c

sub2()

...

l
mmmmemme-

l
e

|
compile

compile

only

linker

executable
program

VMS

ULTRIX

CC PGM

-c

pgm.cC

SUB1

-c

subl.c

SUB2

-c

sub2.c

LINK PGM,SUB1,SUB2

1d pgm.o

subl.o

-functions-

Programming in C

Basic

function

return x to

/* pow -

- page 51

syntax

the power y

double

pow(x,

/* base */

double x;

/* exponent */

long y;

body

-——-

return

(

...

name

[return typeld

);

([Cparmlistl)

Cparmlist declarationsl;
{
body
}

More power and complexity than a single statement.

independent building block

Take time to become familiar with existing libraries,

default return type is

to avoid re-inventing the wheel.

reverse

char

(s)

sC1;
{
3

"int"

Programming

in C

-functions-

Non-integer

Function must

#include

page

functions

declared

the

calling function

<(stdio.h>

main()

{
short

convert():

long j;

convert

(j);

3
short

convert

(num)

long num;

If a function return
integer is assumed.

is not declared

The return statement
will be converted to

expression
the type of

the

QUESTION:

function.

What

convert

convert(j)

the

data

type

Argument

/* test

page 53

-functions-

Programming in C

passing

integer power function

main()

{
short

1i;
short power();

for

0; i ¢ 10; ++1i)
printf("%d %d\n",

power(2,

1i));

AUTOMATIC STORAGE
i

I
|
|

|
|
l

copy of variable

PARAMETER STACK

Precise usages of

==)>

parameter

the terms

called function:
formal parameter,
parameter, real

lst param

stack

"argument"

In calling function:
actual parameter, actual
dummy argument;

and

argument,

formal argument,
argument;

"parameter":

Programming

-functions-

Argument

power

raise

passing

integer

page

(continued)

integer

n-th

power

* /

short
int

power(x,

short

/*base*/
n;

/ *exponent*/

{
short

for

p=1

(

;

p‘ * =

--n)

return(p);

|
l

actual

Always

What

widened

does
~

aria

before

arguments

the
-

sta
:

int,

|
l
|

in parameter
long,

double.

look

as we

o asm

de o

stack:

ter

enter

the

Pt
T

AN
IR

SRS

after

UMD

power
T

call:

ARENNS

QUESTION:

|
|
|

Width of

STACK

SHECTGES

|
|

PARAMETER

STORAGE

AUTOMATIC

Programming

-functions-

Recursive

#include

page

functions

{(stdio.h>

main()

{
long

factorial();

printf
exit

("3

factorial

%d\n",
factorial

(3));

(0);

3
/*

factorial

return

A /

long factorial(n)
long n;

parameter,

local

storage

£
if

1)
return

(1)

return

else

factorial(n

}

Variables declared within a function
are

local to that function and
come into being with the dynamic
invocation of the function.

They disappear

function

termination.

parameter stack comes into being with the
dynamic invocation of the function.
It disappears
at function termination.

1)):

Programming

-functions-

Initializing automatic

"initializer"

Automatic

arrays

scalars

may be

an automatic

page

attached

scalar

CAN be

(but

not

initialized

the

declaration

an array).

in VAX-11C.

main()

£
char ¢ = 'x’;
short i = 1;
short j = 1 &
printf("%d

exit

%d %c\n",

c);

(0):;

QUESTION:

What

The

does

this

intialization
executed

each

program print?

done

time

the

instructions

function

that

entered.

main()

{
short

receipt();

printf ("First

printf("Second
exit

%d\n",
=

%d\n",

(0);

]

short

receipt()

{
short
return

number

(number++)
;

QUESTION:

What

does

this

program

print?

receipt());
receipt());

are

-functions-

Programming in C

Storage

page 57

class

Picture of C program in computer memory

contains the machine instructions
for

DATA

STACK

the

program

contains variables which remain in
FIXED locations -- "static" storage

contains automatic variables

arguments, and function-call
bookkeeping; changes as functions
are called and returned

Programming

-functions-

Static

Internal

storage

page

class

static:

Declared inside a function or block, and is known
only

inside

otays

put;

Remembers

that

block

not

values

between

Initialization

the

loaded

into

(private

the

memory).

stack.
function

done only
machlne

once,

calls.

when

the

main()

short

receipt():;

printf ("First = %d\n", receipt());
printf("Second = %d\n", receipt());

exit (0);
3

short

receipt()

{
static

short

return

(number++)
;

number

}

QUESTION:

What

the

output

this

program?

program

Programming

Static

-functions-

storage

class

page

(continued)

External static:

Data

that

common

(global)

several

functions

Declared OUTSIDE the body of any function
Shared by

all

source

file

#include

functions

that

rand

that

{(stdio.h>

static Short rnum = 0;
/*

return a

/* random number */

random

short

integer

short

rand()

{
rnum

|
=

rnum

return

(rnum

}

12047
>>

13911;

/*period=8192+*/

1);

;

/* srand - set random seed
x /

int

srand(seed)

short

seed;
{
rnum

seed;

QUESTION: In which memory
DATA, or STACK?

TEXT,

segment does

rnum

reside:

Programming

in C

-functions-

page

Initializing arrays

UNIX

static

arrays

automatic

- VMS

static

data

initialized

link

initialized

into

the

program file

time

static

short

static

char

initialized

cannot

both static and automatic arrays can
be

can be

arrays

digits(101 = {0,1,2,3,4,5,6,7,8,93;
= "hello, world";

msglfl3]

the array bound

is bigger

than the number of

initializers, the extra elements are
initialized to zero.
- If

QUESTION:

the array bound is less
initializers, a compiler

no bound is given,
of initializers.

What

are

the

than the number of
error is generated.

taken to be

intial values?

static char st[(51 =:"std";

static char sC21 =

static

short

al51

static

short

bLC1

static

char

xC1

the number

"abc';

{1,

33;

{1,

"abc";

73;

I
|

|
I

I
I

I
|

I
I

Programming in C

~-functions-

- External

data

that

page 61

variables

common

declared outside

(global)

several

functions

the body of any function

functions that wish to share access to external data
use

the

#include

extern

keyword

(stdio.h>

short a =

/*external data can be

main()
{
extern short a;
short 1 = 17;
long

1 = subfn (i);
if

25)

long subfn

(arg)

short arg;
{
extern

short

arg;

;ééurn ( ... )3
I

initializedx/

Programming in C

-functions-

storage

class

int x;

data will be allocated
instead of

reduce

page 62

in general purpose

registers,

memory

execution time

since a memory access

is not

needed

for variables

that are used often,

eg.

loop index

VAX-11C will ignore - it will choose which variables
to place

into

registers

int

power(x,

int

{
register

int

}

Cannot

take address

(&)

For maximum portability, register should be
used only with
int
and pointer wvariables.
However, most compilers will do sensible
things with
char
and
short
register
declarations, also.
he
X

Programming

in C

-functions-

Scope

Internal

data

page 63

rules§

(local)

data declared inside a function is known only within
that

function

data can be declared inside any compound statement
(formed with curly braces)
data declared
block

in a block

(BLOCK)
known

only within
|

that

main()

short

if (i <= 25)

{
float
i

1i;

3el0;

|
External

data

3
(global)

data declared outside the body of a function in
a source file is known to all functions that
follow in that source file

static data declared outside
in a

source

in any
0

other

non-static

function
function
keyword

file

canNOT be

source

the body of a function
made

known

function

file

data declared

outside

the

body

in a source file is made known to any
in any source file with the
extern

Function_names are external by default.

Programming

in C

-functions-

Initialization

Scalars

once,

constant

short lim = BUFSIZ + 1;
char separator = ‘\n’;

static

Arrays

summary

initialized to constants
expressions:

static

1initialized to lists of constants,
padded with zeros:
static

short

static

char buflC5121

static

char

arC51
sC]

{1,
=

53;

{01;

"dog&cat";

Auto storage (stack), and register storage (register)
are initialized every time the function is entered.

Scalars

short

initialized
a

expressions:

int

Arrays

cannot

—

can be

initialized

326

buf

[31

char msgll =
short tim[5]

"dog";
y 2,

in auto
auto

storage

(UNIX)

(VMS)

with

irregularities

{'d’',’0o’,'g’};
-

char

initialized

some

page

External or static storage is initialized only
into the program file at link time.
They stay put in fixed locations.

pan'

33;

/*legal*/

/*illegal - compiler errork/
/A*NOT padded with zeroes*/

Programming in C

~-functions-

Empty brackets:

three

page

cases
in C

As parameter to function,

TP IO

they are a synonym for

address

long

setstr

char

slC1];

(s)

(--

receives

the address

of array

With array initializer, they mean "take the size from
the

count

static

initializers."

short xC

{0123,

0456,

07773;

With an external array, they mean "the bound will
be specified by the actual data declaration”

extern short y[];‘

Programming in C

-functions-

Passes

page 66

of C compiler

Preprocessor: expand macros, compile-time constants,
#include files, and conditional compilation

Parser: translate program‘into a logical

Code generator: translate
- assembler code

Assembler:

tree-structure

Linker:

produce

language

this

relocatable

tree

into

object

from

the

symbolic

assembler

link

the

relocatable

code

together with other

code

object
object

files

Programming in C

-preprocessor-

page 67

Define

#define
the

token-string

preprocessor

replaces

all

occurences

of ID with 'token-string’ after this defining instance.
‘token-string’ is scanned for previously defined ID’s.

Example

#define FAIL
#def ine EOF

(EOF

== getchar())
exit (FAIL);

becomes
if

(-1

1
-1

(in-line

== getchar())
exit(1l);

Dangerous

example:

#define RABBIT

Define

Style

(RABBIT # RABBIT)

can also be done
cc

code)

-DRT1l=1

rules:
put #

command

line

in UNIX

pgm.c

column

use

uppercase

put

all

names

#defines

before

any data declarations

Programming

in C

~preprocessor-

Define

Example

and macros

(macro):

#define SQUARE(n)
#include (stdio.h>

n *n

main()

{
char x[1001;
short i:;

SQUARE(xLil);

becomes

(in-line

code):

x(ild

xCil;

QUESTION: Write the in-line code for SQUARE(x+1).
Fix the definition.

page

page 69

-preprocessor-

Programming in C

Macros (continuéd)
<

(x))

(y)) 2 (y)

#define MAX(X, V)

(((x)

g#define MIN(x, )

(((x)< (y)) 2 (x) = (y))

#define ABS(x)

(((x)

¢ 0) ? -(x)

(x))

"Generic"”

- accept any data type

Efficiency

- in-line code, no call and return

Preprocessor lines are taken one at
a time; they can be continued by
placing a '\’ at the end of the line.

(((x) < (y)) 2 \

#define MIN(x, y)

(x)

(y))

Continuation possible for any C statement
static char msgll =

"very long...

line";

But if string fits on one line, prefer
static char msgll =
"very long ...

line”

Don’t put side-effects on arguments

ABS(++n)

SUGGESTION:

==>

(((++n)

< 0)

? -(++n)

(++n))

Write function first.

Make macro only when needed.
(Function is less prone to
programming errors.)

Undef - To remove the latest definition:
#undef

Rarely used in practical programming.

Programming

-preprocessor -

page

Include

®)

#include
Causes
with

"filename"

this

the

line

entire

to be
file

replaced

‘filename’

F'or personal or project header files
The
(1)

(2)
(3)

UNIX compiler
the directory

searches
containing the C progranm,
directories specified in the compile command,
"standard places."

The VAX-11C compiler searches
(1) the current default directory
(2) the directory containing the C program

#include

For

system-wide header

The

UNIX compiler searches
dlrectorles specified in
"standard places."

(1)
(2)

files

the

compile

command

The VAX-11C

(1)

compiler searches
SYSSLIBRARY - a standard directory

Header

file.h

files

are

usually named:

where

Includes may be nested

file

any

filename.

(discouraged).

Programming in C

~preprocessor-

Conditional

#if

page 71

compilation

constant-expression
or

#ifdef

ID
or

#ifndef

(any C or preprocessor statements)
#else

(any C or preprocessor statements)
#endif

#if

constant-expression
is true if constant-expression
evaluates

#ifdef

#ifndef

ID
is

nonzero

true

'ID’

has been defined.

ID
is true

‘'ID’

has

not been defined.

Programming

in C

-preprocessor-

Conditional

compilation examples

Env1ronment

dependencies

#ifdef

USHORT

#define ushort
#else
#def ine ushort
#endif

Simulating hardware

page

(adapted

unsigned

from

stdtyp. h)

short

on mainframe

#ifdef UNIX
static
static

char buffer [481C801 =
char *bufp = &buffer;

O0;

#else
static

char

#bufp

0x8000;

#endif

Safe
|

way

to
/*

nest

#include

"sandwich"

around header

#ifndef SOMENAME
... text of header
#endif

"Tuning" for size
#if MAXTOKEN < 128
#define TOKEN char
#else
#define TOKEN ushort
#endif

Including TRYOUT main with function
...
(code for function)

#ifdef

file

TRYOQUT

main()

{
(code

#endif

test

function)

Programming in C

-preprocessor-

page

Line

#line

line-number

can be used to reset the line-number
and/or ID which is passed to the compiler.

/*test.c -

0 and o are mixed up in string name

main()

{
char
®

[£251;

strcpy

(so,

"test

string");

test.c

"test.c",

/*test.c

line

23:

so undefined

- 0 and o are mixed up in string name
#line used to change compiler error msg

* /

main()

{
char

#line 37 COPY
strcpy

[£251;

(so,

"test

string");

% cc

COPY,

test.c

line

37:

so undefined

Programming

in C

-pointers-

What

A pointer

another

holds

pointer?

the

address

variable.

short

*p;

i = 0;

page

are short

a pointer

short

(&)

&i;

p gets

*p;

that

address

which

pointed

p*/

thus:
p;&i’jzkp;

the

same

as:

j = 1i;

short

#*p;

read

"declare

declaration

p as

short

the variable

pointer"

J = *pi
is

read

"set

assigning
#p

has

the

that which

variable

pointed

lvalues,

meanings

"Address-of"

(&)

can

not

QUESTION:

Which of

the

applied

only

rvalues.

following are

&i;

&(>(1i

1);

&(i

1);

ILLEGAL?

Programming in C

-pointers-

page 75

Declaring and using pointers

short #pi, *pj,
long *pl;
double *pd;

pi, pl, pd are the pointers; they are lvalues.
*pi, *pl, *pd are references to the objects
pointed to;

variable

they are also

address

1100

/*pi,pj are pointers to short/
/*pl is pointer to long*/
/*pd is pointer to double*/

contents

1300

1100

1350

‘

I
I
|

|
20 |
|

1380

1350

|
pl

1400

1410

|
1410

l
1430

1440

|
0.0

!
pd

lvalues.

|
1430

Programming

in C

Simple

examples

short *pi, *pj,
long *pl;
double *pd;

using pointers

*pd += *pi;

Api = 4pl;

Pj = pi;

*pJ /= 3;

++pJ;

(Apj)++;

++pl;

/*pil,pj
1is
1s

/*pl
/*pd

&t;

1100

1300

|”

1100

1350

14
20

1380

1350

1400

1410

1430

1440

page

-pointers-

1430

are pointers to short*/
pointer to longx/
pointer to doublex*/

Programming

in C

Pointers

page

~pointers-

function arguments:

swap

Call by value; C cannot directly
alter function arguments in caller.
To change the arguments in the caller,

pass pointers

int

badswap(i,

short

{

]

to be altered.

int

swap(pi,

short

short
t

to the variables

#*pi,

pj)

*pj;

ghort t;

*pi;

*pl = *pj;
*pj = t;

This simply changes
the local i and j.

This is called:
swap(&x, &vy);

Programming in C

-pointers-

Pointers as function arguments:

int

page

scanf

short
float

y;
z;

nargs

scanf ("%dxhd%f",

&x,

&y,

&z);

Reads from standard input:
368
23
87.62
nargs tells how many successful assignments.
separators are whitespace: spaces, tabs, newlines

Input

Use

this

call:

FFFF7421

scanf
( "%8x",

&status)

8-digit hex

ABC

int number

,sCanf("%c%c%c", &cl, &c2, &c3)
Three

A BC

scanf ("%$s%s%s",

hello

scanf ("%s",

contiguous

characters

sl, s2, s3)
Three separate characters
(into strings)

str)
One

|
"word"

(delimited by whitespace)
hello

scanf ("%80c",

str)
At

499.95

scanf ("%3hd.%2hd",

most

&dols,

Dollars

Using
of

scanf,

characters

there
up

1s no
a

characters

str

&cents)

and

simple way

newline.

into

cents

shorts)

read one

line

Programming in C

-pointers-

page 79

Pointers and arrays

All operations done by array subscripting
can be done - usually faster - with pointers.

short gLl1001];
short

*pq;

pq = &qL01;

/* pg gets address of the

zeroeth element of gq */

equivalent

/*q

700

equivalent

to &qLO01*/

1200

|- ===~ |
|
5 |
| =-==- |
|

10
|

i
|

|
|

| -——-- ]

495

| --=-- |
|
|
| ----- |
1300

| ~===~ e
|

| ~==-- |
|
I

| ===-- |

|-=--- |

If we

then write:

What does

i have

type

tvpe

glnl

i
in

*pq;

it?

»Declaration:

short gL100] is read

Expression:

qlnl

"array of

100

read

shorts"”

"q sub n"

Programming

in C

-pointers-

Pointers

Whenever

and arrays

(con‘t.)

are used in arithmetic
integer constants and variables

scaled by

the

storage

double

*pd;

short

*pi;

2);

the

*(pd

7);

/*
/*

Example:

&gC31

&qlC31

gqCL31

size

the

pointer.

e.qg.:

X
= x(pi

page

pointers

expressions,
are

Generally

is
2

the

is
8

first multiplied by

(the

size

short)

first multiplied by */

(the

size

a double)

short ql(51;

1200

gqL01

gCll

|
|
| ————|
|
|

qC21

qgC31

|
|
| - ===

1206

gf4l

1208

342

3%2

1is

(g +

glnl

*(g + n)

| ===~
|

| ===
|

1200

1202
1204

page 81

-pointers-

Programming in C

Pointer and array examples:

index.c

/* index - return index of first occurrence of char ¢
*
*

in string s
SUBSCRIPTED version

* /

{(stdio.h>

#include

int

index(s,

c¢)

/*string to be searchedx*/
/*search character*/

char sC1;
char c¢;
{
short

while

(sCil

‘'\0’

&& sCild

¢ 2 1

!= c)

++1;

return

(sCil

-1);

}

/* index - return index of first occurrence of char c
in string s
POINTER version

*
*

* /

({(stdio.h>

#include

int

index(s,

c¢)

char *s;
char c;

/*string to be searched*/
/ *search characterx/
{
char

*s0

while

(*s

'"\0’

&& #s

++S;

return
}

(#s

7?2

-1});

Programming

in C

-pointers-

Array arguments:

page

strncpy

When arrays are passed to functions, what
C really passes is a pointer to the array.

strncpy - copy n characters
string
sl

from

string

char

*strncpy(sl,

char

*#sl,

unsigned

s2,

*s2;
int

{
char

*oldp

sl;

“while

(n--

Aksl++
return

*s52++;

(oldp);

strncpy will

(1)

calls:

strncpy(al,

a2,

DIM);

where

(2)

strncpy(&allf0l1,

&a2001,

and a2

are

arrays:

char

QUESTION:

strncpy

What

declared as

allDIMl,

the

a2CDIM1;

type

DIM);

Programming

-pointers-

Array

QUESTION:

Assume

just

arguments:

the

before

question

following machine

calling

ADDRESS

STORAGE

line

800

|
1800

What does the
strncpy(save,

T
B

What
when

save

parameter stack look
line, 4) is entered?

|
l
!
|
l
!

1lst

does the storage
strncpy returns?

1800

state

strncpy(save,

VARIABLE

save

page

line,

\0O

I
2z

|
w

like when

param

save

1look

-pointers-

Programming in C

Array arguments:

read

{(stdio. h>

#include
/* read
*/

page

unsigned

read

int

char sC1;
unsigned int

characters

read

(s,

into an array

n)
/* where to store the bytes
/* max no. of bytes to read

{
int 1i;
char c¢;
for

)

{
getchar();

== EOF)
return

sCi++]d

(¢

(i);

'"\n’)
return

(i)
;

3
return

( i);

EXAMPLE
read

(array,

10) I 4

lst

param

char

sC1;

IS REWRITTEN BY C TO

BECOME:

char

+*s;

(A POINTER TO CHARACTERS)

read #*/
%/

Programming

in C

-pointers-

Array arguments:

write

write the

page

write

characters

from

an array

unsigned

char

int

write

int

(s,

s(C1;

unsigned

/* location of bytes to write
/* how many bytes to write */

Snsigned int j;
for (j = 0;

j < n; ++3)

putchar(sCjl);
return

(n):;

QUESTION: What does the parameter stack look like after
following function

("0",

their

1lst

param

1lst

param

MNEION

SIS
MRS

ONDIRE

"abc"

arguments?

CUPARNT

write

("abc",

set

EAOTD

write

calls

400

500

!
|

o’

the

\NO

!
|
|

Programming in C

-pointers-

page

Pointer arithmetic

Adding or subtracting pointers and
will cause C to scale according to
storage size pointed to.

integers
the

Pointers may be subtracted from each other (scaled).

Pointers to like types may be meaningfully
compared with each other.

Pointers may be assigned or compared against 0.
C guarantees
char

that

no data

item will

ever be at

*p;

NULL)
return;

NULL:

QUESTION:

stdio.h

If &sCO1 == 1000, what address will receive 7777

short

*ptr;

char

slL201;

ptr

A(ptr+3)

777;

Programming

in C

-pointers-

Multidimensional

static

short

arrays

scoresC71[91

{
o,

o0,

0O,

o,
o,

0,
1,

0,
0,

O,
0,

O,
O,

2, 3,1,
o, 7, 0,
o0, 0, 0,

O,
O,
O,

0’

l’

OI
0,

o0,

};

Arrays are
subscripts

stored in rows, that
vary the fastest.

scores L[21C31
o

is,

sizeof

(scores)

sizeof

(scores[01)

sizeof

(scoresC01L01)

shortl[9]

tyvype

QUESTIONS :

scoresl(2]

right

&scoresCO01C0]

1200,

what

&scores[11L01]
scores(1]

Passing a multidimensional
X

where

sumup

sumup(scores,

short

short
short

array to a function:
7);

declared

sumup(arr,
arrl1[9];
nrows;

nrows)

page

Programming in C |

~pointers-

Pointer

short

arrays

#aptrl103];

declares

aptr

pointers

to be
short.

an array

static

char *citiesC1

{HNYN’

"PHILA",

cities

1000

1103

QUESTION:

1113

|
]
l

|
|
|

l
O

i
L

Write down

citiesC21C21

&cities[21C21

xcitieslC2]

i
1113

|
|

|
S

|
\O

NULL};

|
1109

ten

1109

1100

"LA",

1103

HBOSH’

1100

page 88

|
\0

the TYPE and VALUE of

Programming in C

-pointers-

Command

line arguments

When main()

called

page

to C

is passed

two arguments:
main

(ac,

av)

unsigned int
char *avLl1l;

passed

the

count of

the main.

av is a pointer

the number

to a

One

ULTRIX interface

cmd al a?2

avC0]
avlCl]l
avlL2]
avLC 3]

list of name pointers.

types:

VMS

interface

cmd al

1400

1404

of arguments

cmd =

and the program sees

ac;

"Ssys$login:cmd.exe"
a2

the following variables:

} 1440 :
I

1440

1662

1444
1448

1666
1669

{ a ! 1 ! \0 :
E a E 2 ; \0 E

1452

Programming

in C

-pointers-

Using arguments

#include

{(stdio.h>

main(ac,

av)

unsigned

int

char

page

echo.c

ac;

*avL1];

{
short

1i;

for (i = 1; i ¢ ac;
printf(i ¢ ac-1 ?

++i)
"%s "

"%s\n",

avlil);
~exit

(0);

o Example
S

echo

2200

2204

xyz

12345

| ___

3750 | e

| c

: 2630 :

avC0l

2630

| 3750 |

| h

| o |

\O |

avCll
avl2]
avL31
avL41

2634
2638
2642
2644

: 3755 : 3755 : a : b : \ 0 :
|
: 3758 : 3758 { X : y : y/ : \0 |
: 3762 : 3762 { 1 : 2 : 3 : & | 5 | \O |
:
0 :.
i
|

Programming

Variable

-pointers-

number

Taking the address
to walk this list:

functi on arguments:

char

*cpystr(olddest,

char

#*olddest;

char

+*s;

the

argument

char

for

(src

—

pointer

olddest I 4

w—
s

!= NULL; src

Src

(#Asrc

A++ps)

‘A0")

*de st++
Adest

allows

*src;

ApsS;

while

list

cpystr

{
char **ps = &s;
register char *dest
register

page

ksrc++;

‘A0’
;

return (olddest):;
3
Walking
call

the

pointer
ps
al ong the arguments allow user
function with vari able number of arguments:

cpystr(target,

olddest

1300

"ab"

2000]

1304 | 3000]
1308 3“55;5|
1312 | 31301
1316 :—-_5_:

"C“’

2000

3000

3050

3130

| ===~ |
|
l

src

dest ; “““““ ;
|

| ~===m
|

NULL);

e|
|

\0|

| === |

| ===~ |

lldefl’

| ~===m- |
|

\O]

| ===

- |

| === |
|

\O]

Programming

in C

-pointers-

Pointers

page

to functions

Funcfiions themselves cannot be directly

manipulated but
can be.

pointers

the

functions

void f(g)
void

(*qg)();

pointer

(*g)(i);

to function */

call

g(i)

}

For

example:

short fnl (arg)
short

/xthe first function/

arg;

{
'
if (arg < 5) return
else return (11);

short

fn2

short

arg;

(arqg)

(10);

/*the

second function*/

{
if (arg < 5) return
else return (21);

(20);

int

func

short
short

(g,

/*the

calling function*/

(4g)();
1i;

{
printf

("%d\n",

(*g)(i));

main()
o~

{

func

(fnl,

7);

will

func

(fn2,

3);

will

Programming

in C

-structures-

page

Structure basics

A structure

is a group of variables,

which
1is placed together

for

ease

of varying type,

manipulation.

- Formal definition§of structure variable
(define
struct

the pattern)

task

{
char

job

[201;

char *plan;
short start;

float

length;

Declare

structure variables

(actually allocate
struct

task

job

from

the

pattern

storage)

e e+

et it
ettt P +

plan

start

——— +

+———t-——+

length

+—-————- +

struct

task

ti,

tj,

tk;

declares

three variables:

on VAX:

sizeof

(ti)

ti,

tj,

tk.

(bytes).

Programming in C

-structures-

Members

page 94

structures

The member of
a structure
is used in expressions:
structurename.member

e.qg.

t.plan
or

tk.length

element

type

t.job
t.plan
t.start
t.length

char [£201]
char *
short
float

offset

in structure

0
20
24
26

EXAMPLE:
in

task.h header

struct

file:

task
{

char job [201;
char #*plan;
short start;
float length;

};
in prog.c
#include
#include

program file:
"task.h"
{(stdio.h>

main()

{
static

struct task tl = {"Hawaii vacation",
"car-plane", 1210, 8.451;

printf ("%s
%s
%d
%8.2f",
tl.job, tl.plan, tl.start,
}

tl.length);
.

Programming in C

-structures-

Members and nesting

)

structure.member

is an lvalue

Examples:

(tj.start

(

ti.start)

tk.lengtfi.; 12.3;
tl.plan

ptr;

One structure may be nested inside another.
struct

time
{
char hh;
char mm;
char ss;

};
struct

task

{
char job [C20];
char *plan;
struct time start;
float length;

};
struct

task t;

can now reference the

t.start.hh
t.start.mm
t.start.ss

components of each time:

page 95

Programming

in C

-structures-

Defined

types

structures

the

structure as

Common usage #define

for

page

a new variable

EXAMPLE
:

task.h header

#define
TASK

TASK

file:

struct

task

{
char

job

char

*plan;

short
float

[201;

start;

length;

};
in prog.c

#include
#include

program file:

"task.h"
<(stdio.h>

main()

{
static

TASK

tl = {"Hawaii wvacation",
"car-plane", 1210, 8.453;

printf

("%s
%s
%d
%8.2f",
tl.job, tl.plan, tl.start,

tl.length);

Programming in C

~gstructures-

Pointers

structures

Only a few operators are allowed upon structures:
t.plan

member

address-of

sizeof

(t)

Structures

e.qg.

page

size

cannot be operated upon as a unit

tj;

/ *generally not workx/
/* but works in VAX-11Cx/

The declaration:
struct

task

#*ptask;

declares ptask to point

to a structure of

type task.

ptask = &t;

To access members
pointed

the

structure

to by ptask:
ptask->job
or

ptask->plan
or

ptask->start.mm

ptask->length

the

same as

(Aptask)
. length

t.plan

the

same as

(&t)->plan

Programming

in C

~-structures-

Pointers

structures

page

(continued)

are

often used to pass

functions.

EXAMPLE:

/*function

add a

task

#include
int

structure

‘

"task.h"

install

struct

(ptask)

task *ptask;

{
ptask->job ...
ptask->plan ...

ptask->start.mm

return (...);
}

called

from

the

main()

num = install

by:

(&ti);

...

to a

task

table

Programming in C

®)

-structures-

Formats

for

struct

task
{

structure

char

page

definitions

STRUCTURE FORM and
ACTUAL STRUCTURES

*desc;

long plan;

}
tskl,

)

struct

tsk?2:

task
{

char

STRUCTURE FORM only

*desc;

long plan;

};

®)

struct

ACTUAL

STRUCTURES

only

ACTUAL

STRUCTURES

from

{
char *desc:;
long plan;

}

struct

tskl,

tsk?2:;

task

tskl,tsk2;

previously defined
STRUCTURE FORM

Programming

in C

-structures-

page

100

Unions

structure-like

objects

variable

One

variables,

varying

values

i.e.

types

overlay

one

(not

follow one another

use:

two

ways

and widths

in one

variable

another

in a

structure)

looking at

the

same

storage.

union

{
long

char

clC41;

parts;

}
1 and ¢ are
can be held

two objects which
in the variable
parts.

parts.l

then

0x87654321

parts.cL0]
parts.clfl]
parts.cl2]

=
=
=

0x21
0x43
0x65

parts.clL3]1

0x87

Another use:§saving space in data storage by using the
same

space for mutually-exclusive values.

union payeeno

{
char

ssnoll21;

char

taxidnoll1l51;

A union will be large enough to hold the
Alignment will satisfy all uses.

the

track of

programmers

how the

recently used.

task

union was

keep

most

largest member.

Programming

in C

-structures-

page

Typedef

is a method of
for

language not part

the C

types.

creating

synonyms

This

preprocessor.

Instead of:
#define bool
We

could

say:
typedef

typedef

int

bool;

char *STRING;
STRING s, t;

part

the

101

Programming

in C

-structures-

Arrays
of

Consider

the

problem

structures

looking up

a keyword in a predefined table and
mapping it into an integer "token" for

the
1

book
2

is
3

on
4

In header file

struct

page

this
5

efficiency.

desk
6

(token.h)

keytab

{
char *word:;
int token:;

};:

word

l
l

token

program:

static

struct keytab dtabll
{
"define", 1,
"include", 2,
"undef
", 3,
"line", 4,
"ifdef", 5,
"ifndef", 6,
"endif",

"elseif",
};

102

Programming in C

Arrays

~structures-

structures

page 103

(continued)

/*function to lookup a keyword in a table
of keytab structures and return the token
A/

'"token.h"

#include

int

lookup

(keyword,

table,

char *keyword;
struct keytab #table;
short tablesize;

tablesize)

/ *keyword to lookupk/
/*ptr to table of structures*/
/*number of entries in tablex/

{

for

(

;

tablesize
if

;

(cmpstr(keyword,
return

return
3

Called from main()

typ

+---—-- +

4————- +

tablesize|

== +

/*failurex/

as:

dtab,

8);

\0OJ

o
-+

+——— - +

4 4+

table->word))

o
- -+

+————— +

table

++table)

(table->token);

(0);

lookup("line",

keyword |

--tablesize,

Ie
bttt +

| m——— |

| -===- |

e
e

]

\0Of
+

e
e
- +-

——————— >l

|----- ]

ln]

jlul|l

d]|

\O|

ee
- -+

|
2
|
| ===~ |
|
|
|

| === —- |

| = ;

T+

- >l

\OJ|

Programming

in C

-structures-

Bit

Represent

Useful
Useful

page

fields

data as

bit

field

instead

if storage is limited
for defining status words,

#define

bits

struct

flags

unsigned

bytes

hardware

int

{
bits

alloc:1;
type:3;
ref:2;
sc:3;

bits

bits
bits

};
struct flags

104

FEach individual field is
and may be referenced:

n bits

long

f.alloc
or

f.sc
etc.

ref

type

alloc

interfaces,

Programming

in C

-structures-

Bit

fields

f.alloc

turn

test:
if

(f.sc

==
e

Can‘t

Unnamed

Field

Do not

not

(&)

field.

are used

for

alignment

causes

padding.

overlap unsigned boundary;

aligned at

depend

varies

unsigned.

cannot

field

left

fields

of width

Fields

take address

the

off:
f.type

page

(continued)

To set oh:
to

the

on allocation

between machines.

right,

combine

mask-and-shift

not

right

bit-field

unsigned.

order within word;
(some CPUs order bits
left as in VAX, PDP)

operations

operations.

and

105

Programming

in C

-structures-

Linked

slight

the

struct

linked

our

lists

task

{

char *plan;
short start;

float

};

task

length;

structure

(chains)

struct task *next;
char 7jobl[201;

struct

106

lists

re-definition

creation

page

will

tasks:

allow

Programming

in C

-structures-

Linked

list

struct

task

struct

task #*p;

page

(continued)

*tlist;

To add an element

to a

task

point

to new task

linked

current head

list:

p = malloc(sizeof (struct task));
p->next

tlist,

tlist

To delete an element from a task linked list:
p

tlist,

free(p);

tlist

107

p-J>next;

Programming

Standard

in C

input,

~-Clibrary-

standard

stdin

Standard

input

stdout

Standard

output

stderr

Standard

error

These

three

output,

and

page

standard

error

file

files

are

already

opened for

the main

program.

The default for all

three

files

the

interactive

terminal.

| ~ === |
l

stdin
|
terminal-----=--==~-- >

stdout

|- >

|
|

cmd

terminal

stderr

- === >

terminal

| ====--- |

The
|

stdin and stdout can be
individual commands

changed

VMS

for

UNIX

ASSIGN filel
ASSIGN file2
RUN CMD

SYSSINPUT
SYSsOUTPUT

cmd <{filel

| -=—===- l

stdin

file

i
l

-——=--=—-eu-- >

|
|

stdout

| === >
|

cmd

>file2

stderr

file

108

Programming in C

Character

-Clibrary-

Input/Output:

page 109

getchar,

putchar

Basic'I/O facility:
read a character at a time from the "standard" input
write a character at a time to the "standard" output

Get a character from the standard input:

char getchar()
getchar gets a character from stdin. (c >= 0)
getchar returns EOF (-1) on end of file.

Put a character to the
char

standard output

putchar(c)

putchar puts

character ¢

stdout,

returns

(c must be >=0).
putchar returns EOF on error.

File

copy:

while

((c

= getchar())

!= EOF)

putchar(c);

getchar and putchar are typically implemented as
macros,

not

functions.

Programming

in C

Line

-Clibrary-

Input/Output:

gets,

gets

text

line

from

puts

text

line

char

stdout.

‘'\0’'

terminator

newline

returns

from

string at

(a)
(b)

gets

stdin.

characters

character

The

puts

*gets(s)

copies

stdin

newline
EOF

added.

deleted.

its

argument.

int puts(s)
copies from character string
at
to stdout, appending a newline.

no value

the

until:

copy

returned.

input

output:

puts(gets(s));

page

110

Programming

in C

~Clibrary-

Formatted

printf(fmt,

fmt

output:

argl,

returns

the

characters

...)

string

...

are

that

number
are

specifying format

the

output

variables

static
int

characters
to

the

written

standard

sC]1

"abc"

printf

("%5s",

s);

==)

__abc

printf

("-5s",

s);

==)

abc

printf

("-5.2s",

=#>

printf

("%54d",

printf

("%-54",

printf

("%xd4",

If output
width

s):

1i);

==)

1i);

i);

==>

is too wide for
ignored.

==)

out

output

37;

char

output

format

EXAMPLES
:

short

printf

arg2,

page

"output width",

111

Programming

in C

-Clibrary-

page

Formatted input:'scanf
0

scanf (fmt,

&argl,

fmt

-argl,

&arg2

...

string

&argn)

specifying format
to be

... are the variables
in that format

input

scanf returns the number of arguments
successfully assigned.
Characters are read from the standard input
The scan is terminated if the format
character does not match the input.
Codes for scanf are the same as for printf,
except that "hd", "ho", and "hx" read shorts.

Input items are separated by whitespace,
which is ignored.
The ‘¢’ format is an

exception;

the requested number of characters are always read
including whitespace characters.
(only EOF stops the scan)

EXAMPLES
:
int i;
short 7j;

char

scanf

slC201,

("%d%hd",
will

scanf

&i,

&j);

produce

("%d%d",
will

scanf

s2L201;

&i,

cause

("%2d%hd",

("%20c",
the

scanf

j==132

value

overwrite

&j);

(==

356

&i,

i==35, j==
in terminal

(==
characters

("%[abclx%lxyzl",
will

132

(==

s);

&j);

will produce
241 is still

scanf

i==26,

(==

produce

sl,

s2);

sl=="bac",

132
adjacent

241

buffer

test msgll2s$}I*&”
go

into

(==

bacyxw

s2=="yx"

112

Programming

I/0

in C

~Clibrary-

to and from strings:

write args

sprintf,

will

sscanf

into a string according to fmt

char str [141;
static har month L1031
short day = 23;
sprintf

page

(str,

produce

"%10s

str

"November";

%44",

month,

"November

day);

23"

read into érgs from string according to fmt

static

char

str

[]

"Hammer

568";

char part [61]1;
long number;

sscanf (str,

"%s%d", part, &number);

will produce

part

"Hammer",

number==568

113

Programming in C

-Clibrary-

F'ile

page 114

1/0

A FILE is a structure

file descriptor:

specifying...

0 STDIN,

STDOUT,

2 STDERR,

characters left in buffer
mode
next character in buffer
buffer

from

stdio.h:

#define FILE struct _iobuf

FILE pointers:

stdin, stdout, stderr

file descriptors:

fopen

opens a file by name,
FILE *fopen

(fname,

specified mode

mode)

EXAMPLE :

FILE *fp;

fp = fopen ("data.file",
mode

"w",

open for
mode

"w");

seqgential write

"r"

open for sequential
mode

"a"

append:

fclose

read

(fp)

Closes a file controlled by fp.

open for writing at

end

Programming

-Clibrary-

File

Character

I/0

(continued)

1/0

getc(fp)

putc(c,

fp)

fgetc(fp)
fputc(c,

Line

page

macro

/% function %/
fp)

function

I/0

fgets(s,

fp)

read

most

n-1

chars

into

including newline
fputs(s,

fp)

write

Formatted

file

fmt,

fprintf(fp,

&argl,

...,

&argn)

argl,

...,

argn)

fmt,

Block

1/0

fread

(buf, size, num,
read num items

fwrite

I/0

fscanf(fp,

(buf,

write

fp)
of size

size,

num,

fp)

num

items

size

each

into buf

each from buf

115

Programming

/&
*
* /

#include

-Clibrary-

prage

Program

to use C standard I/0 to write a
containing one 1, two 2s, etc. up to 10

file

{(stdio.h>

main()

{
FILE *fptr;
char string [101;
register i, j;

/*Create

the

file

* /

((fptr = fopen ("FILE.DAT",
perror ("OPEN error"),

/*Place
*

the

correct

write

the

(i=1

;

i<{(=10

for

(3j=0

numbers

array

the

"w")) == NULL)
exit (0);

the

array

string and

file

* /

for

i++)

;

j<i

{

string

(fwrite

; j++)
Lj1 = 1i;

(string,

perror

("WRITE

fptr)

error"),

exit

3
/%Close
* /
if

the

(fclose

file

(fptr)

perror

EOF)

("CLOSE error"),

exit

(0);

116

Programming

Error

~Clibrary-

output:

perror,

page

fprintf

perror'("file open error'");

write string to stderr

-and-

write system message
to stderr that
corresponds to the error code in
the external int
errno

fprintf

(stderr,

write

"can’'t open file %s\n",

formatted output

stderr

fname);

117

Programming

in C

-Clibrary-

System

an alternative

direct

calls

(emulated

I/0

standard

the

I/0

(fopen,

ULTRIX operating

fwrite,

system

in VMS)

creat will create adnew file:

returns

mode

level

page

file

creat

specifies

(name,

mode)

descriptor

(positive

UNIX access

permissions:

owner

group

read

0400

040

write

0200

020

execute

0100

010

open

will

open

already

integer)

others

existing

file:

fd = open (name, mode);
returns

mode

file

==
==

1
2

close will

descriptor

(positive

for read,
for write,
for read/write.

close a file:

close(fd);

integer)

...)

118

Programming

in C

-Clibrary-

System

1/0

(continued)

read and write:

read(fd,

read

size bytes

returns

write

size

returns

buf,

size);

into buf

from fd

the number of bytes
0
if end-of-file
-1

(fd,

buf,

size);

from buf

number
1f

read

error

bytes

the
-1

page

to fd

bytes

INPUT

written

error

EXAMPLE:

copy

#include

<{(stdio.h>

OUTPUT

main()

{
char bLBUFSIZI1;
short i
int

fdin,

((fdin

fdout;

open ("INPUT",

perror
if

((fdout

creat

perror

while

((i

{
if

("open

("OUTPUT",

("creat

read

0))

error"'"),

(fdin,

(1 ¢ 0)
perror('"read

0))

error"),

-1)

exit

(1);

-1)

exit

BUFSIZ))

error"),

(1);

exit

(1);

else if (i != write(fdout, b, i))
perror('"write error"), exit (1);
exit

3
(0);

3
From

stdio.h:

BUFSIZ

(512

on most

systems)

119

Programming

in C

-Clibrary-

page

120

lseek

lseek will

position within

lseek

origin

returns

number

offset

bytes

for

read/write

origin);

from

the

origin

byte

offset

byte

offset

from the beginning,
from the current position,

byte

offset

from the

the

l1seek does

offset,

open file

resulting offset

not

specifies

(fd,

location from the beginning

physically move

the

byte

end.

position

the

for

disk arm;

the

I/0

only

operation.

EXAMPLE:

/*function to read randomly a block from a file
Ny

#include

<(stdio.h>

int getblock(fd,

buf,

blkno)

int fd;
char *buf:;
short

/*file desc of open filex/
/*address to read intox/

blkno;

/*block number

readx/

bytes

read

{
lseek

(fd,

/*return T

blkno
or

FF'==
T >

BUFSIZ,

0):

F wvalue:

for

end

number

file

* /

return
.

(read(fd,

buf,

BUFSIZ)

BUFSIZ);

Programming in C

~Clibrary-

Heap allocation:

malloc

- allocates

page

malloc, free

space on the heap.

char *malloc(nbytes)
unsigned nbytes;

An element of size nbytes 1is
allocated, and its address

malloc()

returned.

returns NULL pointer on failure.

free - frees a previously allocated cell.

free(pcell)
char *pcell;

Free

the

space pointed
to by pcell.

Be careful
-

to free only those

malloc’ed!

cells previously

121

Programming

-style-

C programming

page

style

Data and variables

Consistent

and meaningful names

Standard defined-types: ushort, tiny,
#define ushort unsigned
#define tiny char

Manifest constants: EOF; NULL,

short

122

Programming

-style-

C programming

page

stvyle

Operators

blank

for

primary

plL1l

and

unary

ops:

5.m

No blank for parens:

(x + vy)

No blank for functions

f(x)

One

blank

for

binary

One

blank

for

key words:

not

assume

ops:

(...)

left-to-right

evaluation:

a()

not

+ b()

assume

c()

timing of

side-effects

within

expression:

ali++1

bLj++1;

ali++1

bLil;

BAD

The

only guarantees

are

the

sequence

full-expr

for

sequence and

guarantees

| |

side-effects

’

123

Programming

in C

-style-

C programming

Control

Braces

above

page

stvyle:

structures

and below body

{
remark("bad value",

code):

++nerrs;

One-tab

uniform

80-char

line

"else-if"

- Avoid

indents

limit:

"wrapped

only when necessary;

"goto"

and

"continue"

lines"

prefer

"switch"

124

Programming

in C

-style-

C programming

page

style:

Functions

Layout:

#include <{(stdio.h>
#include <(stdtyp.h>
#include "proj.h"
#define TOK short
TYPEX varx = NNN;
/* comment
* /

describing

TYPE func(al,

a2,

commented

func

a3)

TYPE1l al;
TYPEZ a2;

/* describe
/* describe

*/
%/

TYPE3

/* describe

a3;

{
extern TYPEX varx:;

(local

declarations>

(statements>
3

Build and use standard headers

Source

files

functions

#includes,

no bigger

then

Prefer

lines;

lines

then

in header

rest

files;

#define,

declarations,

static

“Defensive

than

nothing but

structure

than 500

#defines,

initializations

contain

no bigger

file

they

should

typedef,

and

externs.

each

source

to external

programming":

responsible to avoid
Professional code is

file

out-of bounds references.
not allowed to "bomb-out".

125

Programming

in C

-style-

page

Common C bugs

General
Uninitalized wvariables
Off-by-one errors.

Treating an array as though it were
l-origin (instead of 0O-origin).
Unclosed comments.
|
Forgetting semi-colons.
Misplaced braces.

Types, Operators, and Expressions
Using "char" instead of "int" for

the
returned value from getch.
"Backslash" typed as "Slash"; e.qg.,
~'/n’

instead

'O.

Declaring function arguments

after the
function brace, creating spurious
local variables.
Arithmetic overflow.
,
Using relational operators on strings;
e.g.

strcmp(s,

"end"

instead

Using "=" instead of "=="
Multiple side-effects to the
in

the

"end").

same

same memory

expression;

e.g. sec = ++sec % 60;
False assumptions about the time at which
post-increment is done.
Off-by-one errors in loops with increment.
Precedence of bitwise logical operators.

(Always parenthesize them.)
numbers

Right-shifting negative
Assuming

(Not
the

equivalent to division).
order of evaluation of expressions.

Forgetting null-terminator

strings.

126

Common C bugs

Control

page 127

-style-

Programming in C

(continued)

flow

"else"

Misplaced

Missing "break" in "switch".
Loop with first or last case abnormal
Loop mistakenly never entered.

in some way.

Functions and program structure
Wrong type

arguments

(relying on memory instead of manual).

Wrong order

of arguments.

Omitting static on subfunction’s abiding storage.
Assuming that static storage is re-initialized at
each re-entry.

Macro written without full parenthesization of
arguments

and

result.

Pointers

and arrays

Passing pointer

instead of value

-- or value

instead of pointer.
Confusing "char" with "char

#".
Using pointers for strings without allocating
storage for the string.
Dangling pointer references -- references to
storage no longer used.
Confusing single quotes ('\n’)
with double quotes ("\n").

Programming in C

-labs-

MONDAY PROGRAMMING

the

page 128

ASSIGNMENTS

In the following exercises, avoid explanding the scope of
exercises so as to involve sophisticated terminal input.

For example in exercise 1, avoid generalizing so as
sum of numbers up to that input from the terminal.

l. Write a program to form the sum of
inclusive.
Print to the terminal the
average of the numbers.

2. Write a program that
and prints them back to

the numbers
sum and the

form

from 1 to
integer

the

reads 5 characters from the terminal
the terminal in reverse order.

3. Write a program that will read characters from the terminal
until newline and print back to the terminal a line of
asterisks proportional in length to the binary value of each
character typed.
Apply a scaling factor, so that the largest
ASCII

character will

still

fit

program functions as a simple
as an analog input signal.

Write a program
back to the

prints

letter

typed as

that reads 2
terminal the
input

computer

on which you

a program which reads

Write

our

and

purposes,

prints
1s

are

numbers
larger.

to your

5. Write a program which tells
bits, i.e. tells how many bits

terminal

onto an
plotter,

character

treating

line.

the

input

This
line

from the terminal and
What happens if a

program?

the size of
exist in an

a machine word
int
on the

running.

each word
sequence

an
on

line
a

input

separate

from the

line.

non-whitespace

A word,

for

characters.

Along with each word, print its hash-sum (the sum of the
characters in the word), once as a 4-digit hex number and once
as a 5-digit octal number.
Print the hex number with leading
zeroes and the octal number with leading blanks.
An empty line
of input should produce no output.

Programming in C

-labs-

page 129

TUESDAY PROGRAMMING ASSIGNMENTS

In the following exercises, avoid expanding the scope of
the exercises so as to involve sophisticated terminal input.

J1.

Write a function that compares 2 shorts

and returns the

larger.

(passed as arguments)

Test the function with a progranm.

/2. Write a macro DO which will duplicate the syntax of a
FORTRAN DO

loop,

e.qg.

DO i=3,11,2
written as
DO(i,3,11,2)
meaning a loop from an initial value of i = 3 to a final

value = 11 in increments of 2.
The variable name, the limits
of the loop and the increment are arguments.
Test the macro
with a program that prints to the terminal the values of the
loop during each pass.

3. a. Write a function cmpstr (sl, s2) which returns a true
value if strings sl and s2 are equal, a false value otherwise.
Compile

with

cmpstr

into an object

file.

Write a program to test cmpstr.

cmpstr.

Compile it and link it
|

4. Write a macro TOUPPER which will translate a lower case
character into upper case using the conditional operator e.g.
a ? x : vy Test the macro with a program which reads characters
from the terminal and prints back to the terminal the result of
the TOUPPER macro

them.

5. The function nfrom (low,high) produces a random number
between low and high inclusive.
See page 5-24 of the text.
Modify nfrom to generate a
1long
value rather than a
short
one.
Write a program that calls nfrom 10,000 times to generate
random numbers from 1 to 6.
Print to the terminal a summary
showing how many

ls,

2s,

etc.

were generated.

6. Modify the program calling nfrom in the prior exercise to
simulate 10,000 rolls of two six-sided dice.
Print a summary
showing each possible sum and how many times it occurred.

Programming in C

~-labs-

page

130

WEDNESDAY PROGRAMMING ASSIGNMENT

1. Write a program that will populate a 50
with the integers 1-50 using pointers, not
the array to the terminal on five lines

element char array
subscripts.
Print

2. Write a program that reads your first name and age from the
terminal using a single
scanf
and forms a character string
using sprintf
with your age at your next 3 birthdays.
Print
the character string back to the terminal.
3. WHrite the
page 7-10 of

function
the text

an appropriate

rindex
described in Exercise 7-1 on
"Learning to Program in C".
Test with

program.

Modify the function
to use pointers rather

cmpstr
written
than subscripts.

in a

previous exercise
Test with a program.

5. Multidimensional arrays will be needed for this exercise.
See the appropriate pages of the text and this workbook for
assistance.
The program
tokens.c
converts its input into a
table of tokens.
©See the supplied listing. A token is defined
as a unique number assigned to a word.
The first word from the
input is assigned to token number 1, the next is assigned to
token number 2, etc.
When a word is found in the input that is
identical to one encountered previously, it is given the same

token number previously assigned.
After reading all the input,
the program prints out the table of token numbers and words.
If a word is longer than 8 characters, only the first 8 are
stored.

Write
consists

the functions required by tokens.
Your solution
of only one source file, with 2 functions:
short install
char sC1;

(s)

/*Look for

the word

the

table.

found,

return its token number.
If not found, insert
s in the table and return a new token number.

If
int

space

execution
S

run

ABC
1

exit

(FAIL);*/

dumptok()
/*%Print

ocample

left,

out

the

tokens.c:

tokens

123

ABC

213

Token table:
1 ABC
2 123
3 12345678

1234567890

token

table%/

Programming

in C

~labs-

page

131

THURSDAY PROGRAMMING ASSIGNMENTS

Write

a program to prompt for and read from the terminal
values for part name (maximum chars 10), part number

the

(6 digits)
into

and amount

a disk file

Write

a program that
terminal your first

the
on

successive

middle

name

Write

name

file

lines

and

stock.

using a

program
created

uses

name,

using

first

Obtain and write

array

middle

pointers

name

the pointer

and

array

Make

Write

page

last
as

the

8-5

8-7

that

will

read

the

above

and

the

program
the

text

program

the text
sentence of the

gettt.c.

last

your

records
the

records

read

name.

last

revisions

described

"Learning

runtt

part

report

stock of

8-1

each

C".

in Exercise

Program

and print

from
Print

name,

the
a

in Exercise

Program

described

"Learning

exercise

from

terminal

showing the part name, part number and amount
the total amount in stock of all parts.

such

name.

and

page

structure.

8-2

in C".
Ignore the
out the structure

Programming

in C

-labs-

page

FRIDAY PROGRAMMING ASSIGNMENTS

1. Write a program that reads its 2 arguments from the command
line.
If the strings are equal, print EQUAL and the string.
If the strings are not equal, print NOT EQUAL.
If less than
or more than 2 arguments are supplied, print an appropriate
error

message.

2. Revise the program previously written to create a part
number file to create and write to the file using
system

level

1/0.

3. Write a program that will read the records using system
level 1I/0 from the part name file created above and print to
the terminal a report showing the part name, part number and
amount in stock of each and the total amount in stock of all
parts.

132