Basics Of C Program

8/13/2019 Basics Of C Program

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Learning Outcomes

History of CA glance at a simple C program, its

compilation and execution

Data types

Variables

Keywords

Constants

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Learning Outcomes

Console IOScope of a variable

Storage class specifiers

Structure of the C program

Compilation model

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History of C

BCPL (Basic Combined Programming

Language): mid 60s

B: 1970

C: 1971

Originally designed for and implementedon UNIX system by Dennis Ritchie.

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Simple C program/* First C Program */

main()

{

printf("Hello, my first C program");

}

1

2

3 4

1. Comment

2. Program execution begin here

3. Block

4. Special type of statement that prints on the console.

5. A statement must end with a semicolon.

5

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Simple C program

/* First C Program */main(){

printf("Hello, my first C program")

}

Compile

hello.obj

hello.c

File name

runHello, my first C program

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Comments

Statements of information

Single line comment

//This is a// program for addition

Multi-line comment

/*This is a programfor addition*/

Why should we

commentour program?

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Data types

Denotes kinds of data Primary data types

Integral types:

char, int

Floating point types:

float, double

Derived types

long int, short int, unsigned int, shortunsigned int etc.

Secondary data types

array, pointer, structure, union, enum LaterRAGHUDATHESH GP

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Sizes of primary types

char:

1 byte, ranging from -128 to 127

int:

2 bytes, ranging from -32768 to 32767

float :

4 bytes, ranging from -3.4e38 to 3.4e38

double:

8 bytes, ranging from -1.7e308 to1.7e308

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Derived Types

From the primary types char, int, float,double, many more types called derivedtypes can be formed.

Apart from that, unsigned and signed canalso be specified to integral typesdepending on need.

Example: unsigned char gives range from 0 to 255 which is

actually what we want since ASCIIvalues also have the same range.

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long and short

long int : 4 bytes

short int: 2 bytes which is same as int

short int that can also be written as short.

long int can also be written as long

?

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Data types (primary and derived)

Data type Bytes Range

signed char 1 -128 to 127

unsigned char 1 0 to 255

short signed int 2 -32768 to 32767

short unsigned int 2 0 to 65535

long signed int 4 -2147483648 to2147483647

long unsigned int 4 0 to 4294967295

float 4 -3.4e38 to 3.4e38

double 8 -1.7e308 to

1.7e308

long double 10 -1.7e4932 to

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Declaration statement

General format:

datatype variableName;

Example:

int x;

float y;

char c; But what is avariable ?

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Variables

A variable has a name and represents the

memory location where a value (s) is

stored.

Every variable is associated with a data

type indicating the kind of data it stores.

Variable has to be declared in the program

so that compiler and runtime environment

can determine memory depending on its

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Rules for variable names

Combination of alphabets, digits and

underscore

First character must be an alphabet

No commas or blanks

Some compiler restrict the names of the

variables only up to 8 characters. Must not be a keyword.

Examples: interest, pay_roll, pay_roll_07

?

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Variable declaration and initialization

Declare and then initialize

int i;

i=50;

int i,j;

i=20;j=20;

Declare and initialize together

int i = 50;

int i, j;

i=j=20;

Variable declaration must be the first statement in

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Keywords

Words in the C language whose meaning

are already defined

Keywords cannot be used as variable

names. They are reserved words

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32 keywords in C

auto double int struct

break else long switch

case enum register typedef

char extern return union

const float short unsigned

continue for signed voiddefault goto sizeof volatile

do if static while

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Constants

A constant is a value that does not change

C allows us to use the following constants Integer constants

Real or Floating Point (Float) constants

Logical constants

Character constants

String constants

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Rules for integer constants

Must have at least one digit Can be either positive or negative. If no sign

precedes the constant, it is positive

Range allowed: 216to 216-1 or (-32768 to

32767)2 bytes Examples: 43, 343, -54, -5678

Cannot have decimal points

For integers that hold up to 4 bytes suffix lor L

Example : 5677188199292L, 67L

67L is forcing the computer to allocate 4

bytes for 67 instead of 2 bytes.

?

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Octal constants

A leading 0 can be specified to indicate

that the integer constant is octal (base 8)

Counting from 0 through 8 in octal looks

like this: 0 1 2 3 4 5 6 7 10

int seven = 07; // decimal value 7

int eight = 010; // decimal value 8

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Hexadecimal constants

A leading 0x or 0X can be specified to

indicate that the integer constant is

hexadecimal (base 16).

Counting from 0 through 15 in hex looks

like this: 0 1 2 3 4 5 6 7 8 9 a b c d e f

int x=0X1; // decimal 1

int x=0xf; // decimal 15

What is the decimal equivalent of 0x11?

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Rules for real constants

Must have at least one digit Can be either positive or negative. If no

sign precedes the constant, it is positive

Must have a decimal point

Examples: +76.66, 76.0, -67.87

Can also be expressed in exponential form:

Example: 4.5e-6, 4,1e1, 6.7E9, -9.7E7

Note that e can be either in lower case orupper case.

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Rules for logical constants

A value representing True or False

Non-zero value is true

Zero is false

Example:

1 ( representing a true)

0 (representing a false), 8.7, -45 ( representing a true)

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Rules for character constants

Single alphabet, digit or special symbol

Should be enclosed within single invertedcommas

Since characters are internally treated asintegers, the ASCII values of character iswhat is stored internally.

For example ASCII for Ais 65. Range : -128 to 127

Example: C,7,Escape sequence

like\n

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Escape Sequence

Escape sequences are characters which are

not associated with any particular letter.

For example, a new line character: \n.

It is so called because it uses a \ to escape

the meaning of the character next to it.

What if we want a character constant withvalue ?

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Escape sequence character table

\n New line

\b Backspace

\f Form feed

\ Single quote

\\ Backslash

\t Tab

\r Carriage return

\a Alert

\ Double quote

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Rules for string constants

A set of characters enclosed within double

inverted commas

Example:

Let us learn C,

\Hello\,

7

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#define

#define is used to associate a constant with a

name which can be used in the program.

Syntax:

#define constant-namevalue

Example:

#define PI 3.14

What is the advantage of associating a name

with the constant ?

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Console Output

printf() is an inbuilt function used to displayoutput on the console (screen).

General form:

printf(,)

%c: for printing characters

%d for printing integers

%f for floating point

%s for strings

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Program to add two numbers (1)

/*Addition of two numbers*/main(){

int a, b, sum;

a=10;

b=2;

sum=a+b;

printf("a=%d, b=%d, sum=%d",

a,b,sum);

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Console input

scanf() is an inbuilt function used to

accept input that users enter through the

keyboard.

General form:

scanf(,

&)

Note the & symbol. & indicates

address.

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Program to add two numbers (2)

/*Addition of two numbers*/

main(){

int a, b, sum;

printf("please enter the value ofa and b");

scanf("%d%d",&a,&b);

sum=a+b;

printf("a=%d, b=%d, sum=%d",a,b,sum);

}

Read and store the

values entered into

memory location

allocated for a and b.

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Question?

What will happen if you try to print &a, &b

and &sum in the previous code?

printf("a=%d, b=%d, sum=%d",

&a,&b,&sum);

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Scope of variables

Global

-- declared outside all functions

-- accessible to all statements in theprogram

Local

declared inside functions accessible to statements within the

function where declared

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Example

int j=10;main(){

int a=20;

printf("a=%d, a);

printf(j=%d, j);

}

fun(){

printf("a=%d, a);printf(j=%d, j);

}

Some other function

Global variable

Local variable

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Storage Class Specifiers

Variables have data types and storageclasses associated with them

A variables storage class denotes

where the variable will be stored (memory /CPU registers)

what its default value will be (that is, if novalue is assigned)

the scope of the variable

the lifespan of the variable

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Types of Storage Class Specifiers

automatic

register

static

externWe will deal with this in the functions chapte

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Automatic storage class

Storage: memory

Default value: unpredictable value /

garbage

Scope: local to the block where it is

defined

Lifespan: till the control remains in the

block where it is defined

Example: auto int sum;

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Register storage class

Storage: CPU registers

Default value: unpredictable value / garbage

Scope: local to the block where it is defined

Lifespan: till the control remains in the blockwhere it is defined

Example: register int sum;

Advantage in declaring a variable as registerstorage class is faster access. Variables that

are used very often can be declared as this.

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Compilation model

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Learning Outcomes

OperatorsType Conversion

Flow Control Statements

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Operators

Arithmetic Binary

Arithmetic Unary

Relational

Logical

Bitwise

Conditional

Assignment

A symbol that denotes an operationthat can be performed on some data

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A ith ti Bi


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Arithmetic Binary

Operation Operator Example Result

Addition + a+b 30

Subtraction - a-b -10

Multiplication * a*b 200

Division / a/b 0

Modulo % 10%20 10

Assume the following declaration:

int a=10,b=20;

20) 10( 0

- 0

10

Back to

School

Applicable only to integral types. The sign of the result is the

same as that of the numerator.3RAGHUDATHESH GP

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Arithmetic Unary

Sign Operator: + -

Example: +5, -5

Increment and Decrement by 1 ++ --

Pre-increment

y=++x; (x=x+1; and y=x;)

Post-increment

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Relational operators

Operators used tocompare two operands(variables, constants orexpressions)

Characters can becompared as well

These operators areused extensively withflow control statements.

Operator Meaning

< less than

> greater than

= greater than

or equal to

== equal to

!= not equal toExamples:

a!=b, a


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Logical Operators: &&

To be used when a statement or set ofstatements are to be executed based onwhether two expressions are true

The expression on the RHS will beevaluated only if the expression on theLHS is true.

Example: (x>10)&&(y


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Logical Operators: ||

To be used when a statement or set ofstatements are to be executed based onwhether at least any one of two

expressions are true The expression on the RHS will be

evaluated only if the expression on theLHS is false.

Example: (x>10)||(y


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Truth table for && and ||

expression 1 expression 2 exp1&&exp2 exp1||exp2

0 0 0 0

0 non-zeronumber

0 1

non-zero

number

0 0 1

non-zero

number

non-zero

number

1 1

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Logical operators

Logical not: !

to used when the truth value of an expression

is to be reversed

Example: !(x>10)

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~

~1 00000001 (1s complement)1s complement11111110

How to find the decimal equivalent of 11111110?

Since the sign bit is 1 the number is negative.

To get the decimal value ofve number get the binary

equivalent of 2s complement and convert it to decimal

2s complement -( 1s complement + 1)

1s complement of 11111110 0000000100000001

+ 1

-------------

00000010 decimal value 2. Hence the number is -2.

Back to School

Sign bit

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Conditional operators

? :

Also known as ternary operators as they work onthree operands

condition ? expression 1 : expression 2

Example: z=x>y?10:15

If condition results in true valueexecute expression 1

If condition results in false value

execute expression 2

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Assignment operator

=

variable=expression;

Assigns the value of the expression to the

variable

Examples: a=b, a=10, a=x+y, a=x++,

a=++x

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Compound Operators

expression equivalentx=x+1 x+=1

x=x-1 x-=1

x=x*(5+10) x*=(5+10)x=x/(5+10) x/= (5+10)

x=x%20 x%=20

+= -= *= /= %= >>= >>>=


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sizeof

Returns the number of bytes the operand

occupies in memory.

Example:

sizeof(float)

sizeof(2)

int x=9;

sizeof(x) ;

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Predict the output

1.printf(%d, -5%-3);

2.printf("%d",10j) && (j++>i);

printf("%d",j);5.printf(%d,!-1);


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Conversions

What happens when two variables of differentdata types are used in an expression?

For example, what happens when a variable

of type int is added to a variable of type float?

When two operands are of different types,

then the operand that has smaller size is

converted to the type of the operand of larger

size before the operation is performed. This is

implicit or widening conversion.


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Implicit conversionThe implicit conversion in the direction

indicated happens automatically to one of theoperands when the operands of different typesare used.

charintlong intfloatdouble

If one of the operands is signed, the other is

automatically converted to signed.

When a variable of type int is added to avariable of type float, implicit type conversion

takes place where the variable of type int is

promoted to a float before the operation is done.18RAGHUDATHESH GP ASST PROF

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Type Casting

Implicit conversion is done by the compiler

automatically.

Sometimes we may need to change

implicit behavior

In such cases we must explicitly request

the compiler by using a cast operator.

Cast operator: (datatype)


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Example

int i=10, j=20;

float f;

f=i/j;

printf(%f, f); prints 0.0

But

f=(float)i/j;prints 0.500000

Casting i to float type.20RAGHUDATHESH GP ASST PROF

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Predict the output

char c=127;

char c1=c+2;

printf("%d",c1);

char c=127;

printf("%d",c+2);


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PrecedenceOperators Associativity

--------------------------------------------------------[] . () -> . left to right

! ~ ++ -- - + * (type) sizeof right to left

* / % left to right

+ - left to right

>> = left to right

== != left to right

& left to right

^ left to right

| left to right

&& left to right

|| left to right

?: left to right

= += -= *= /= >>= >= &= ^= |= left to right

unary


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Control Statements

Statements that enable us to order thesequence of flow of a program.

Decision control statements

ifstatement switch statement

Loopswhilestatement forstatement

do-whilestatement


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if

if (condition is true)

execute this statement;

if (condition is true)

{

execute statement 1;

execute statement 2;

execute statement n;

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Examples for if

if (rate


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if else if (condition is true)


else


if (condition is true){

execute statement 1;execute statement 2;

execute statement n; }

else{execute statement n+1;

execute statement n+2;

execute statement n+m; }26RAGHUDATHESH GP ASST PROF

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Examples for if-else

if (salary>1000)printf(You do not have to pay tax.);

else

printf (You have to pay tax.);

if (salary>1000){printf(You do not have to pay tax.);

printf(But you need to pay asurcharge.);

}else

printf(You have to pay tax.);


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switch switch (integer expression 1){

case integer constant 1:statement 1;

statement 2;

statement n;

default:

statement n+1;

statement n+2;

statement n+m;

}

Can appear0, 1 or more

times for

different

constantvalues

Can appear 0or 1 time


switch exampleC BASICS


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/* This is a menu-driven program forbasic arithmetic operations between twonumbers*/

main(){

int a,b,i;

printf("enter 2 integer numbers separatedby a blank space: ");


printf("please enter \n 1 to add\n 2 tosubtract\n 3 to divide\n 4 tomultiply\n 5 for modulo\n");

scanf("%d",&i);

switch example

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switch(i){C BASICS


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case 1: printf("Result of addition is :%d

",(a+b));

case 2: printf("Result of subtraction is:%d ",(a-b));

case 3: printf("Result of division is :%d

",(a/b));

case 4: printf("Result of multiplicationis :%d ",(a*b));

case 5: printf("Result of modulo is :%d

",(a%b));

default:printf(Inappropriate valueentered");

}

} 30RAGHUDATHESH GP ASST PROF

executionC BASICS


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execution

Execution path 1 :

enter 2 integer numbers separated by a blankspace: 12 2

please enter

1 to add

2 to subtract3 to divide

4 to multiply

5 for modulo

3

Result of division is :6 Result of multiplication is :24

Result of modulo is :0

Inappropriate value entered

You enter this

You enter this


Execution path 2 :C BASICS


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Execution path 2 :

enter 2 integer numbers separated by a blank

space: 10 5

please enter1 to add

2 to subtract

3 to divide

4 to multiply

5 for modulo

1

Result of addition is :15 Result of subtraction is :5Result of division is :2

Result of multiplication is :50 Result of modulo is :0

Inappropriate value entered

You enter this

You enter this


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Fall through problem

Do you see the problem ?

To correct this problem break is used at

the end of each case statement.

It however not necessary to put the break

at the end of the last case or default

statement.

Let us correct the program by including

break.


switch(i){cal2.c

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case 1: printf("Result of addition is :%d

",(a+b));

break;

case 2: printf("Result of subtraction is :%d

",(a-b));

break;

case 3: printf("Result of division is :%d

",(a/b));break;

case 4: printf("Result of multiplication is :%d

",(a*b));

break;case 5: printf("Result of modulo is :%d ",(a%b));

break;

default:printf(Inappropriate value entered");

}} 34RAGHUDATHESH GP ASST PROF

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Execution

enter 2 integer numbers separated by a blank space:12 4

please enter

1 to add

2 to subtract3 to divide

4 to multiply

5 for modulo

2

Result of subtraction is :8

You enter this

You enter this



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Example: case without any statementC BASICS


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Example: case without any statement

main(){

int a,b;char i;

printf("enter 2 integer numbersseparated by a blank space: ");


scanf("%c",&i);

printf("please enter \n a to add\n s to

subtract\n d to divide\n m tomultiply\n o for modulo\n any otherchar to exit\n");

scanf("%c",&i);?

cal3.c


i h(i){

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switch(i){

case 'a':

case 'A': printf("Result of additionis :%d ",(a+b));

break;

case 's':

case 'S': printf("Result ofsubtraction is :%d ",(a-b));

break;

case 'd':

case 'D': printf("Result of divisionis :%d ",(a/b));

break;

Fall through

Fall through

Fall through


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case 'm':

case 'M': printf("Result ofmultiplication is :%d ",(a*b));

break;

case 'o':

case 'O': printf("Result of modulois :%d ",(a%b));

break;

default: exit();

}

}

Fall through

Fall through

Exits out of the program


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while-loop

while(condition is true)statement;

while(condition is true){

statement 1;

statement 2;

statement n;

}


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Example 1

/* program to display numbers divisibleby 2 and 3 between 1 to 100 */

main()

{

int i=1;while(i!=100){

if(i%2==0 && i%3==0)

printf("%d, ",i);

i++;}

}

div1.c


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Example 2Suppose for our calculator program you wantto continue to display the menu until user exits,in such case while can be used.

main(){

int a,b;

char i;

int j=1;

while(j){

printf("enter 2 integer numbersseparated by a blank space: ");


New code added

cal4.c


switch(i){C BASICS


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( ){

//same code

}

printf("\n enter 0 to stop");scanf("%d",&j);

} // end of while loop

}

New code added


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do-while

do-while is same as while with the only exceptionthat the condition is checked only at the end of

the loop.

Therefore do-while guarantees that the statementwithin the loop will execute at least once.

do{

statement(s)

}

while(condition);


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Try out!

How will you change the while-loop of thecalculator program to do-while loop ?

You may find that the do-while loop is more

appropriate in this case since we definitely

need the menu to be displayed at least once!


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for

In example 1 of the while loop, we saw thatwe set up an initial value for int i and thenexecuted the loop until i reached certainvalue, incrementing is value by 1 each time.

This can be more simply achieved through forloop.

for(initialize var;condition;increment var){

statement(s);

}


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Example

/* program to display numbersdivisible by 2 and 3 between 1 to100 this time using for loop */

main(){int i;

for(i=0;i


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Count backwards/* factorial of a number*/

main(){

int num,i,f;

printf("enter a number");

scanf("%d",&num);f=num;

for(i=num-1;i>1;i--)

f=f*i;

printf("%d",f);}


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break in loops

The keywordbreak is used to exit out ofthe loop anytime even when if it does not

satisfy the loop conditions.

When break is encountered the controljumps to the first statement after the loop.


ExampleC BASICS


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p/* program to determine if an integerentered by the user is a prime number */

main(){int num,j,i,flag=1;

printf("enter an integer ");

scanf("%d",&num);

j=num/2;

for (i=2;i


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continue in loop

The continue statement is used to skip therest of the statements in the loop and carry

on with the next iteration.

In other words, when continue isencountered, the control goes to the

beginning of the enclosing loop.


ExampleC BASICS


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Example/* program to determine if an integergreater than 100 entered by the useris a prime number */

main(){

int num,j,i,flag=1;

while(1){

printf("enter an integer greater than100 ");

scanf("%d",&num);

if(num


93/260

for (i=2;i


94/260

Learning Outcomes

Function

Argument Passing

static variable

Command line argumentsRecursion


FunctionC BASICS


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Function

A function is a block of code that performsa particular task.

A function can be called from the same oranother function whenever required. Hence

we can avoid rewriting the same code. Italso improves the readability of theprogram.

Function may take some input in the formof parameters and sent out some output inthe form of return value.


Example1: function without argumentd t t

C BASICS


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and return type

/* Using function :program to determineif an integer greater than 100entered by the user is a prime number*/

int num;

main(){while(1){printf("enter an integer greater than

100 ");scanf("%d",&num);if(num


97/260

p p{int j,i,flag=1;

j=num/2;

for (i=2;i


98/260

return value

Did you notice the warnings that thecompiler throws?

Warning primefun.c 12: Function shouldreturn a value in function main

Warning primefun.c 27: Function shouldreturn a value in function printprime

In fact the first warning has been appearing

ever since we have started C programming.

A function must either return a value or

must be declared as void.


Function declarationC BASICS


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Function declaration return_type function_name(argument-

list)Where argument-list is

Data-type var-name1, Data-type var-name2, Data-type var-namen

If return_type is not specified it is assumed to bean int. argument-list can contain 0 one or more

arguments.

function_name must be unique. It should not clashwith any variable name or other function name.

Variables declared inside the function and theargument-list variables are local to the function.They cannot be accessed outside the function. 6RAGHUDATHESH GP ASST PROF

returnC BASICS


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return

The returnstatement is used to return avalue from a function.

When return is encountered the control go

back to the calling function. Example: return (a);

return (15);

return 0;

return; Used with void. Does not return anything!


Correcting the prime number codeC BASICS


101/260

g p By adding return 0;at the end ofmain()andprintprime() function we can eliminate the

warnings.main(){

return 0;}

printprime(){

return 0;

}

We need to make return type of printprime as void

not int.

primef2c


PrototypingC BASICS


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Prototyping Complier assumes that any C function

would return a type int.

Any function that returns types other thanint must inform the compiler by what is

called prototyping. Prototyping is declaring the function that

needs to be called within the callingfunction.

Note that declaration of a function isdifferent from definition of a function.


Changing the prime number code

C BASICS


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Changing the prime number code

primef3.c

int num;int main(){void pprime();while(1){

printf("enter an integer greater than100 ");scanf("%d",&num);if(num


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Function with parametersC BASICS


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Function with parameters

It is possible for the calling function topass values into the called functionthrough what is called parameters orarguments.

Suppose we declare numvariable insidethemain(), then we will need to passnum into pprime() function since num will

be local to themain() function and so itnot be accessible to thepprime()function.



106/260


107/260

Example of function returning aC BASICS


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value of importance

/* program that has a function whichcalulates the gross salary given thebasic salary*/

main(){double basic,gross;doublecalculateGross(double basic);printf("enter basic salary ");

scanf("%lf",&basic);gross= calculateGross(basic);printf("Gross=%lf",gross);}

gross.c


doublecalculateGross(double basic){double hra,ta,da, gross;

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double hra,ta,da, gross;da=0.5 * basic;

hra=0.1 *basic;if(basic=10000 && basic


110/260

Suppose we attempt to write a code that printsthe number of times a function is called.

main(){void callMe();callMe();callMe();}void callMe(){int count;count++;

printf("you called me %d times\n" ,count);} When we execute the following code it prints

garbage value for count because count is notinitialized.

count1.c


If we initialize count to 0 then print

you called me 1 times three

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you called me 1 times threetimes.

main(){void callMe();callMe();callMe();}

void callMe(){int count=0;count++;printf("you called me %d times\n" ,

count);} This is because the value of count gets

initialized each time the function is called.

What we want is a way in which count value can

be retained.


static variableC BASICS


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static variable

Solution to this is to declare the countvariable as static variable.

Static variables are automatically

initialized the first time to 0. It retains the value between the function

calls.

static can be declared only with thefunction.


Count example correctedC BASICS


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Count example corrected

main(){void callMe();callMe();callMe();

callMe();}void callMe(){static int count;count++;printf("you called me %d times\n" ,

count);}

Prints:you called me 1 timesyou called me 2 timesyou called me 3 times



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void f(int i,int j){printf("In f() before changing : value

C BASICS


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of i=%d and value of j=%d\n", i,j);

i++;j++;

printf("In f() after changing: value ofi=%d and value of j=%d\n", i,j);}

Before calling f(): value of i=0 and value of j=0

In f() before changing : value of i=0 and value of j=0

In f() after changing: value of i=1 and value of j=1

After calling f(): value of i=0 and value of j=0

Result of execution


ObservationC BASICS


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Observation

What do you observe? The parameter values changed in the

called function code are not reflected in the

calling function. This is because the parameters arepassed

by valueto the function.

Both functions have their own copy of thevariables. Only the values of the variablesof the calling function get copied to thevariables of the called function


1000

Addressmain()i

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MEMORY

1001

1002

1003

1004

1005

j 0

0Call f(0,0)

f()i

j

0

0

i++;j++;

1

1i

j

i

j24RAGHUDATHESH GP ASST PROF

main()C BASICS


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i=0

j=0Calls

f()

1000

1001

In memory

i=0

j=0

2000

2001

i++;

j++;

i=1

j=1

Value of i and j

in 1000 and1001 remain

the same!


Call by referenceC BASICS


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Call by reference

What should be done so that the changedvalues of i and j are reflected in the callingfunction?

1. There should be some way in which we

pass the addresses of the variables of iand j from the calling function to thecalled function.

2. The called function should receive thesevariables in a way such that theypointtovalues rather than just receiving thevalues.


Call by reference contC BASICS


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Call by reference cont

&variable-namerepresents the addressof the variable.

Address of a variable is of integer type.

We need a special kind of variable that iscapable of holding an address and using

which we can retrieve the value stored in

the address. Such a kind of variable is called a Pointer.


Introduction to pointersC BASICS


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Introduction to pointers

A pointer is a variable that holds an address of a

variable in memory and using this pointer we can

access the value stored in that location.

Declaration:

Data-type *variable_name; Data-type in the above syntax represents what

type of data the pointer points to.

Example:double i=10;

double *p=&i;28RAGHUDATHESH GP ASST PROF

Getting the address and valueC BASICS


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Getting the address and value

*variable-namereturns the value storedin the address that variable-name points to.

variable-namereturns the address value.

Example:double i=10;

double *p=&i;

printf(%lf,*p);

printf(%d,p);

Prints 10

Prints the address

point.c29RAGHUDATHESH GP ASST PROF

Question ?C BASICS


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Question ?

It is important to specify the appropriate data-type

in the syntax if you want to use pointer arithmetic.

You can use ++ andoperators on the pointer

which allows pointer to jump to next location.

Whether the jump has to be 1 byte , 2 bytes , 4bytes, 8 bytes or 10 bytes is determined by the

data-type of the pointer.

?

The data-type of a pointer variable is always

integer. Then what is the significance of

specifying data-type in the declaration

syntax?

More details on it in the pointers part

of the C story.


Call by referenceC BASICS


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Call by reference/* program : call by value demo */void main(){void f(int *i,int *j);

int i=0, j=0;

printf("Before calling f(): value ofi=%d and value of j=%d\n", i,j);

f(&i,&j);printf("After calling f(): value ofi=%d and value of j=%d\n", i,j);

}


void f(int *i int *j)

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void f(int i,int j){

printf("In f() before changing : valueof i=%d and value of j=%d\n", *i,*j);

(*i)++;

(*j)++;

printf("In f() after changing: value of

i=%d and value of j=%d\n", *i,*j);}


Challenge question?C BASICS


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g q

In the function f() of the previous slide, weused brackets to increment the values of i

and j.

(*i)++;(*j)++;

What will happen if the brackets are

removed? Will the effect be the same?*i++;

*j++;33RAGHUDATHESH GP ASST PROF

RecursionC BASICS


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A function that calls itself is a recursive

function. It is very important that a recursive function

has an exit point. Otherwise it will get intoinfinite loop.

int i;main(){f();}

int f(){i++;if(i>5) return ;f();}

int i;main(){f();}

int f(){f();}

Without termination

condition : infinite loop

Termination

condition

specified.

Executes

successfully.


Prime number using recursionC BASICS


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g

/* prime number using recursion */int num,k;main(){printf("enter an integer ");

scanf("%d",&num);k=prime(2);if(k==0)printf("not prime");elseprintf("prime");}



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Flow

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Assume num=9prime(2) {if(num%i==0) return 0; 9%2!=0i++;2++ 3if(i>num/2) return 1;3>(9/2) No!else

prime(i); prime(3) }

{if(num%i==0) return 0; 9%3i++;

if(i>num/2) return 1;else

prime(i);}

Return value: 0

1

2 3

Return value: 0

4


Attempt another exampleC BASICS


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p p

Write a non-recursive code to generate 10

Fibonacci numbers.


Fibonacci numbersNon-recursive Recursive

C BASICS


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main(){

int f1=0,f2=1,f3,i;printf("%d, %d,",f1,f2);for(i=0;i8) return;

f3=f1+f2;f1=f2; f2=f3;

printf("%d,", f2);count++;fibo(f1,f2);}fib.c

fibr.c

Non recursive Recursive

Termination condition


Use of recursionC BASICS


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Recursive programs sometime seem ratherdifficult in comparison to non-recursive ones.

But in some cases it is actually easier to use

recursion.

For example in cases where you have a

mathematical formula based on iterative value of

n.

For example- factorial value of n. Mathematical formula:

fact(n)= n*fact(n-1) for all n


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main(){int num, res;printf("enter a number");scanf("%d",&num);res=fact(num);

printf("%d",res);}int fact(int n){int f;

if(n==0) return 1;f=n*fact(n-1);return f;} 41RAGHUDATHESH GP ASST PROF

Flownum=3

C BASICS


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num 3

fact(3)

{int f;if(n==1) return 1; n=3f=n*fact(n-1); 3*fact(2)return f;}

{int f;if(n==1) return 1; n=2f=n*fact(n-1); 2*fact(1)return f;}

{int f;if(n==1) return 1; n=1f=n*fact(n-1);return f;}

Return 1

Return 2

Return 6


Challenge!C BASICS


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g

Write recursive code to find the sum ofdigits

First attempt to write the recursive

formula. Then write the code.


Word of caution!C BASICS


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Recursive code may be difficult tounderstand and debug. Hence it should be

used only in places where it makes the

overall program simpler.Recursive code adds to overhead of

multiple function calls.


Learning OutcomesC BASICS


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Arrays

Single dimensional

Multidimensional

Console IO

Unformatted IO

Formatting


ArraysC BASICS


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Suppose you have to work with 100numbers. Imagine the difficulty and time

taken to type in names of 100 variable

names. Arrays are here for our rescue!

Array is a collection of elements of same

data type.


Declaration and Initialization of

Single dimensional array

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Single dimensional array

An array that is a list of elements is a singledimensional array.

data-type variable-name[size]

Example: double prices[10];

A single dimensional array can be initialized withthe declaration statement as shown in theexample given below.

int emp_nums[]={123,111,175,4}

Int emp_nums[4]={123,111,175,4}

An array that is not initialized (and which is notdeclared as static) contains garbage values.


Accessing arraysA l t d i th i d

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Array elements are accessed using the indexposition. Index position begins from 0.

main(){float price[]={120.50,100,175,50};int i;

for(i=0;i


142/260

When the array declaration statement isencountered, memory required for the

array is calculated and contiguous

memory space is allocated. For example, for int size[4]; 4*2=8 bytes contiguous memory space is

allocated.

1000 1002 1004 10085RAGHUDATHESH GP ASST PROF

Strings An array of char is a string

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An array of char is a string.

charc[]={R,i,t,c,h,i,e,\0};

is same as

char c[]=Ritchie;

Note \0 (null) at the end of the first declaration. This

is to indicate the end of the string. Note that the 2nd

declaration does not require this.

To read and print strings simply use:scanf(%s,c);

printf(%s,c);

Note the absence of & sign.Why? Because the value of

is the value of the starting

address of the array !


Two dimensional arrayC BASICS


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Two dimensional array is like a table containing

elements in the intersection of a row and a column. The best example of two dimensional array is a

matrix.

data-type var-name [size][size]

Examples:

int emp_sal[3][2]; can be viewed as:

int k[2][2]={ {12,34},

{13,35}};

int k[][2]={ {12,34},{13,35}} ;

int k[][2]={ {12,34,13,35};

3 rows and

2 columns


/* getting the employee numbers andsalaries of three employees into a 2-dimensional array and displaying them */

C BASICS


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y p y g /main(){

int emp_sal[3][2],i,j;for(i=0;i


146/260

What will happen if array is accessedbeyond its last index?

What is the initial value of array elements

that are not initialized? What will happen index isve?


Functions and arraysC BASICS


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main(){

int a[]={1,2,3,4};int i;f(a);for(i=0;i


148/260

main(){af(a1000)}

1

2

3

4f(a){

a[i]++;}

1000

1002

1004

1008

2

3

4

5

&a[0]

&a[1]

&a[2]

&a[3]


Array and pointerC BASICS


149/260

A pointer variable can be assigned toarrays base address and using the pointer

increment operator all the array elements

can be accessed. Next slide shows the same code that we

wrote in the previous slide using pointers.

Like ++ operator, - - operator can also beused to jump one position before.


main(){int a[]={1,2,3,4};int i;

C BASICS


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int i;

f(a);for(i=0;i


151/260

int

a[3][2]={{1,2},{3,4},{5,6}}; int *p=&a[0];can be viewed as array of arrays where a[0] is

base address of row 1, a[1] is the baseaddress of row 2 etc.

a1

2

3

4

5


Other wonders!C BASICS


152/260

int a[]={1,2,3,4};1.*(a+1) a[1]22.*(2+a)2[a] a[2]3

inta[3][2]={{1,2},{3,4},{5,6}};

a[1][1]*(a[1]+1)*(*(a+1)+1)


String and PointerC BASICS


153/260

main(){chars[]="Shankara";

char *p="Shankara";

printf("%s",s);

printf("%s",p);

}

Both the print statements

print Shankara.

s is an array of characters

p is a pointer to the first

character where Shankara isstored.

Note that the printf()

statement with %s prints the

string char by char withouthaving to increment the array

index or pointer position.


Strings and pointerC BASICS


154/260

Array of strings can be represented in twoways:

char str[][3]

char *str[];(array ofpointers to string)

First way is preferred to read the stringfrom the console.

Second way is the more preferred way tomanipulate and print!


main(){char

names1.c

C BASICS


155/260

n1[][4]={"John","Mary","Sita","Rama"};

int i;char*n2[]={"John","Mary","Sita","Rama"};for(i=0;i


156/260

pointers to string

main(){char *names[4];int i;

for(i=0;i


157/260

main(){char names[6][4];char *nm[4];int i;

for(i=0;i


158/260

Command line arguments are the datathat we can pass through command-line.

The command line arguments arereceived through a special kind of main()function:

main(int argc, char*argv[])

argc holds the number of arguments and

argv contains the address of the stringspassed from the command line.


Example command-line arguments

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main(int argc, char *argv[]){int i;

for(i=0;i


160/260

IO is Input-Output. IO operations deal withreading from various input devices like

keyboard, disk, network and writing to various

output devices like VDU, disk, network etc.

C programming language by itself does notsupport IO. But C compiler writers have written

several libraries which can be included in our C

program to do IO. printf() and scanf() are thus library functions.


Console IOC BASICS


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Reading from the keyboard and writing on to thescreen.

Two types of functions

Unformatted

Formatted Formatted functions allows us to display the data

in the way that we want. For example, if we wantto display price with only 2 decimal places, thenit is possible only with the formatted IOfunctions.


Unformatted functions to read char

getchar(), getche(), getch()

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getchar(), getche(), getch()

getche(), getch()return the input fromthe console. Unlike scanf(), they doesnt wait

for the enter button to be clicked before they

can consume the value typed in. getche() echoes( or displays ) the character

typed in.

getchar() also echoes( or displays ) thecharacter typed in but requires enter button to

be clicked like scanf().25RAGHUDATHESH GP ASST PROF

Back to calculator codemain(){int a b;

C BASICS


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int a,b;

char i;printf("enter 2 integer numbers

separated by a blank space: ");scanf("%d%d",&a,&b);getchar();printf("please enter \n a to add\n

s to subtract\n d to divide\n m to

multiply\n o formodulo\n any other char to exit\n");

i=getchar(); } 26RAGHUDATHESH GP ASST PROF

Unformatted functions to print char

C BASICS


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putch(char c), putchar(char c) Both are same and both print character on

the screen.\

Example:

putch(A);

char ch=B;putchar(ch);


Unformatted functions for strings

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gets() and puts() gets() is used to read string from the

console and puts() is used to print.

scanf() does not work properly in caseswhere a string is composed of multiple

words. scanf() function assumes space

between the words as end of the string. This is where the gets() becomes useful.


Difference scanf() and gets()

main(){

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main(){

char clr[10];

printf("enter a color\n");scanf("%s",clr);

printf(" \n %s",clr);}

main(){char clr[10];

puts("enter a color\n");gets(clr);puts(clr);}

enter a color

light green

light

You enter this

enter a color

light blue

light blue

You enter this


Formattingprintf()can be used to format the output

C BASICS


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p () p

in the way we want to see in the screen. For instance, when we print a double value

we can restrict it to 2 digits after decimal.

printf(formatstring,variables) Formatting characters interpreted moment %

is encountered.

Any character that does not involve a % or\(escape char) passes through straight

without any interpretation and gets printed

as it is


Formatting charactersD C i h

C BASICS


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Data type Conversion char

short signed %d or %i

short unsigned %u

long signed %ld

long unsigned %lu

float %f

double %lf

signed and unsigned char %cstring %s


Format StringC BASICS


169/260

%[special_char][width] ][.precision]conversion char

special_char :

- : Left justify this argument

+: Include a sign (+ or -) with this argument

0: Pad this argument with zeroes

Width: minimum number of characters to print.

Precision: the number of digits to print after the

decimal point


ExampleC BASICS


170/260

main(){int i=10;double d=1245.678;signed short j=-10;

printf("=%5d\n", i);printf("=%+5d\n", i);printf("=%-5d\n", i);printf("=%05d\n", i);

printf("=%+5d\n", j);printf("=%5.2lf\n", d);}

Result:

= 10= +10

=10

=00010

= -10=1245.68


Learning Outcomes

P i t f h t h

C BASICS


171/260

Pointers- summary of what we have seen

so far

Pointer operators

Dynamic memory allocation

Pointer to pointer

Pointer to function


C BASICS


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Pointers- summary of what we

have seen so far


Basics

C BASICS


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int i=10;i: gives the value10&i: gives the address002*(&i): gives the value10

101002

i name

Memory

address

int *j; :pointer to an int

j=&i; :pointer assignment.

j: gives the address of i1002&j: gives the address of j2002*j: give the value of i10

1002

2002

j name

Memory

address

value

value

pointer


1-D array and pointersint a[]={1,2,3,4};

11000 a

*a

C BASICS


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a[0],0[a],*a, *a+0 1

a: base array address

1000

a+2: base array address+22 * sizeof(int)

1000+2*2 bytes

1000+4=1004

1

2

3

4

10021004

1006

a +1a +2

a +3

a

*(a +1)

*(a +2)

*(a +3)

int *b;

b=a;

b: base array address o

array a1000*b: value at 1000 1

*(b+1): value at 10022

1000 b2002


2-D array and pointersint a[2][2]={{5,6},{7,8}};

C BASICS


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a: base array address of array 1000

*a,*a+0, a[0]: value at a2001**a,**(a+0),*(a[0]),*(a[0]+0),a[0][0]:

value at *a5

2001

2004

1001

1002

5

6

2001

2002

7

8

2004

2006

a

a+1

a[0]*aa[1]*(a+1)

**a

**(a+1)

a[0][1],*(a[0]+1),*(*(a+0)+1) 6 5RAGHUDATHESH GP ASST PROF

Pointer Operators *: value at the address specified by the variable

C BASICS


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: value at the address specified by the variable

&: address of the variable ++: increments the pointer by size of the variable

--:decrements the pointer by size of the variable

+: addition of a pointer variable and a constantvalue

-: subtraction of pointer and a constant value and

subtraction of two pointers. ==: comparison of pointers



177/260

Array of pointers Array of pointers to int:

C BASICS


178/260

Array of pointers to int:

int *ptrs[2];int i=10,j=11;

ptrs[0]=&i;

ptrs[1]=&j;

*(ptrs[1]), ptrs[1][0]11

2001

2002

10

11

Array of pointers to int

2001

2002

ptrarr c


Pointer to PointerC BASICS


179/260

A pointer variable that points to anotherpointer variable is a pointer to a pointerrepresented by **.

int i=10int *j;

int **k;

j=&i;

k=&j;

**k10

k

2004 1003

j

10

i

k is a pointer to a pointer to an int


Pointers to function Like variables, functions also have

C BASICS


180/260

,

addresses. A pointer variable can point to anything in

the memory.

Therefore a pointer variable can point to anaddress of a function too.

The next example maintains a function

pointer which points to a particular functionbased on users input and then later

executes that function through the function

pointer.10RAGHUDATHESH GP ASST PROF

main(){int i;

int f();

i ()Prototype declaration

C BASICS


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int g();

int (*fptr)();printf("type 0 for f() or 1 for g() ");

scanf("%d", &i);

if(i)

fptr=g;

else

fptr=f;

(*fptr)();return 0;

}

Prototype declaration

Function pointer

Assigning function addressto function pointer

Calling function through

function pointer


int f(){

printf("f() called");

return 0;

C BASICS


182/260

return 0;

}int g(){

printf("g() called");

return 0;

}

Output:

type 0 for f() or 1 for g() 1

g() called

You type this


Dynamic memory allocation Using arrays we can reserve a fixed memory

location

C BASICS


183/260

location.

Suppose that there can be a maximum of 100

employees in a department and minimum of 2.

In such cases, allocation of 100 locations for a

dept having 2 employee would be utter waste ofspace.

In such cases, we can use dynamic memory

allocation that allows us to allocate memorydynamically as and when required instead of

allocating and reserving it straight away.13RAGHUDATHESH GP ASST PROF


184/260

main(){int *empno, n,i;

printf("enter the number of employees: ");

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scanf("%d",&n);

empno=(int *) malloc(n*2);

if(empno=='\0'){printf("memory not available");

exit(0);}

else

for(i=0;i


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printf("\nemployee number %d : %d\n", i,

*(empno+i));

}Output:

enter the number of employees: 3

enter the employee number: 5432



printing all the employee numbersemployee number 0 : 5432

employee number 1 : 6453

employee number 2 : 7654

You enter this


Learning Outcomes

Structure and its need

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Structure and its need

Syntax

Memory allocation

Passing structure in function

Pointers and structure

Nesting structure

Union

Difference between struct and union

Syntax

Union of structs 1RAGHUDATHESH GP ASST PROF


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Syntax Defining structure:

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struct struct-name{data-type variable-name1;

data-type variable-name2;

data-type variable-namen;

};

Declaring variable of struct-type:

struct struct-name variable-name;

members


ExampleC BASICS


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struct employee{int emp_num;

char name[30];

double salary;};

struct employee emp1,emp2;

defining

declaring


Accessing membersC BASICS


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Structure members can be accessed using. operator on the structure variable.

Example:

emp1.emp_num, emp2.name Structure members can be initialized

during the declaration as:

struct employeeemp={123,Bobby,345.50};


Example- simplestruct emp{int num;

emp1.c

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char name[30];double sal;};struct emp emps;

main(){read();display(); }read(){

printf("enter emp number:");scanf("%d",&emps.num);printf("enter name:");scanf("%s",emps.name); 6RAGHUDATHESH GP ASST PROF

printf("enter salary:");scanf("%lf", &emps.sal); }display(){printf("Displaying data \n");

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printf( Displaying data \n );

printf(" emp number: %d\n", emps.num);printf(" emp name: %s\n",emps.name);printf(" emp salary: %5.2lf\n",emps.sal);}Output:enter emp number:123enter name:Kanakaenter salary:12340

Displaying dataemp number: 123emp name: Kanakaemp salary: 12340.00

You enter this


Examplearray of structuremain(){struct ball{

ball.c

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int size;char color[30];};struct ball b[3];

int i;for(i=0;i


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Output:

enter size of the ball:12enter the color:greenenter size of the ball:13enter the color:red

enter size of the ball:10enter the color:yellowDisplaying databall size: 12ball color: greenball size: 13ball color: redball size: 10ball color: yellow

You enter this


Structure Pointers A pointer variable can be declared that points to a

structure like it points to an ordinary variable

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structure like it points to an ordinary variable.

Example:

struct emp emps={123,"Ganga", 12000};

struct emp *e=&emps;

To access members through structure pointer, aspecial kind of symbol is used.

Example:

enum, ename Structure pointers are required when we pass a

structure variable to a function and we want thechanges made in the variable visible in the callingfunction. 10RAGHUDATHESH GP ASST PROF

struct emp{int num;char name[30];double sal;

emp2.cC BASICS


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double sal;

};main(){struct emp emps={123,"Ganga", 12000};

increment(&emps);display(&emps);}

increment(struct emp *e){e->sal=e->sal*0.10+e->sal;}

123 Ganga 12000

emps.num

emps.name

emps.sal

2001 e

2001 13200


display(struct emp *e){printf("Displaying data \n");printf(" emp number: %d\n",e->num);printf(" emp name: %s\n" e >name);

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printf(" emp name: %s\n",e->name);printf(" emp salary: %5.2lf\n",e->sal);}

Output:Displaying dataemp number: 123emp name: Ganga

emp salary: 13200.00


Nested structure A structure can have as its member a structure

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variable. Example:struct name{char fname[10];

char lname[10];};struct student{struct name nm;

int rollno;} stud; Note: another way of

declaring structure variable13RAGHUDATHESH GP ASST PROF

main(){printf("enter first and last name: ");scanf("%s%s",stud nm fname stud nm lname);

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stud.nm.fname,stud.nm.lname);

printf("\nenter roll number:");scanf("%d", &stud.rollno);printf("displaying data\n");printf("Name:%s %s\n",stud.nm.fname,stud.nm.lname);printf("roll no %d\n", stud.rollno);}

Output:

enter first and last name: John Ray

enter roll number:12345

displaying data

Name:John Ray

roll no 12345 14RAGHUDATHESH GP ASST PROF

unions Union allows variables of different data

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types to share the same memory space.For example, a variable of int type and a

variable of type char share same memory

space. That means this memory space

can be treated either as int or as char.

Union allows us to choose between types

of data based on the requirement of

application.



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Difference between struct andunion

a c[0] c[1]

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struct X{int a;

char c[2];

};

union X{

int a;char c[2];

};

a

1000 1002 1003

c[0] c[1]

1004

a

1000 1002c[0] c[1]1001



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enum gender{male,female};

enum constants

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main(){enum gender g1,g2;g1=male;g2=female;

print(g1);print(g2);}print(enum gender g){if(g==male)printf("Male \n");else

i f(" l ") }

Output:

Male

Female

Assigning any other value would be an error.


Internal working

Internally compiler treats enums as

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Internally compiler treats enums as

integers. Hence the values that enum constants take

start from 0.

In the previous example male is internallystored as 0 and female is 1.

These values can be changed by explicitly :

enum gender{

male=10,female=20};


typedef typedef is used to give a different name to a data type.

Let us understand this with an example:

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struct fullname{char fname[10];

char lname[10];

}; To declare variable of the above type

struct fullname n1,n2;If we have many such declarations throughout thecode then typing this could be tedious.

Using typedef, we could just type

name n1,n2; 22RAGHUDATHESH GP ASST PROF

enum gender{male,female };typedef enum gender GEN;

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struct emp{int num;char name[30];double sal;

GENgen;};typedef struct emp EMP;main(){EMP emps={123,"Ganga", 12000, female};increment(&emps);display(&emps);

}


increment(EMP *e){e->sal=e->sal*0.10+e->sal;}

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display(EMP*e){printf("Displaying data \n");printf(" emp number: %d\n",e->num);printf(" emp name: %s\n",e->name);printf(" emp salary: %5.2lf\n",e->sal);if(e->gen==male)printf(" Gender: Male");

elseprintf(" Gender: Female");}




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Preprocessor directives

#define directives

#include directives

Conditional compilation directives




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Standard Library functions

Standard I/O functions

String functions

Math functions


Preprocessor directivesC BASICS


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Preprocessor directivesare special type of

commands that we

include in C source code.

These directives are

processed before

compilation by a special

kind of program called

preprocessor.3RAGHUDATHESH GP ASST PROF

Structure of a C program

Preprocessor commands (directives)

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Preprocessor commands (directives)

Global declarations

Functions

Statements

Variable declaration statements

Constants in statements

IO statements

Comments (any where in the code)

Must be among the f i rst statements of the prog ram. Only

statement before a direct iv e can be ano ther direct ive! 4RAGHUDATHESH GP ASST PROF

Preprocessor directives types

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#definedirective

#includedirective

#undef directive

Conditional compilation directives


#define #define directive (or a macro) has two

parts:

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string-part

value-part

#define string-part value-part

Whenpreprocessor encounters #define it

replaces the string-part specified in code with

the value-part.

This is useful when the value-part is large and

requires lot of typing or when the value-part is

likely to change. 6RAGHUDATHESH GP ASST PROF

#define PI 3.14

main(){float area(float radius);

string-part

value-part No semicolon!

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float cir(float radius);

float radius;printf("enter radius of the circle: ");scanf("%f",&radius);printf("area is %5.2f\n", area(radius));printf("circumference is %5.2f",

cir(radius));return 0;}

cir.c 7RAGHUDATHESH GP ASST PROF

float area(float radius){return (radius * radius *PI);}float cir(float radius){

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return (2* radius *PI);} Preprocessor replaces all

PI with 3.14. Then

compilation takes place.

Output:

enter the radius of the circle: 13

area is 530.66

circumference is 81.64

You enter this


#define PI 3.14#define PROD radius * PI

main(){

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float area(float radius);float cir(float radius);

float radius;printf("enter radius of the circle: ");scanf("%f",&radius);printf("area is %5.2f\n", area(radius));

printf("circumference is %5.2f",cir(radius));return 0;} 9RAGHUDATHESH GP ASST PROF

float area(float radius){return (radius * PROD);

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}float cir(float radius){return (2* PROD);}


Macro functions

A macro can also be defined with arguments

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just like functions. When an ordinary function is encountered in

the code, the compiler transfers the control to

the function ( a separate memory area). But macros (functions) are expanded in their

places by the preprocessor. So there is no

separate memory area. In fact compilerdoesn't even know the existence of macro

functions.11RAGHUDATHESH GP ASST PROF

#define PI 3.14#define PROD radius *PI#define area(r) (r * PROD)#define cir(r) (2 * PROD)

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( ) ( )

main(){float radius;

printf("enter radius of the circle: ");scanf("%f",&radius);

printf("area is %5.2f\n", area(radius));

printf("circumference is %5.2f",cir(radius));return 0;}

Macro functions. Though not

necessary it is advisable to put the

macro function in parenthesis.

cir2.c

Expanded as: radius * radius *PI12RAGHUDATHESH GP ASST PROF

Word of caution while using macrofunctions

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A macro function can only have onestatement.

There should be no space between macro

function name and argument. area( r ) not ok

If the macro function has involves * and /

then it is advisable to enclose it in bracketsfor it to have desired effect.


#define PI 3#define VOL(radius,height)(PI*radius*radius*height)

den.cC BASICS


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main(){float r=10, h=5, mass=1500;printf("density =%5.2f" ,

mass/VOL(r,h));}

density=mass/volume

According to code : density=1500/ 3*10*10*1500

This is incorrect.This can be corrected by including brackets


#includedirective

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This directive causes a file to be includedas a part of your c code.

The file could contain any valid c code,either a set of functions or preprocessor

directives. In fact the library functions like scanf() and

printf() are provided in a file stdio.h that

some compilers automatically include inthe c code.


int square(int n){return n*n;}

util.h

.h is commonly used

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int cube(int n){return n*n*n;}

int pow(int n, int p){int i,res;res=n;

for(i=1;i


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printf("pow =%d\n", pow(2,3)); }

Output:

square =100

pow =8

#include "util.h: preprocessor searches for

the file in current directory as well as predefined

directories where standard library files are set up.#include : preprocessor searches for the file

only in the predefined directories where standardlibrary

files are set up.17RAGHUDATHESH GP ASST PROF

Conditional compilation directives Conditional compilation directives allow us to

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specify when the compiler should compile a setof statements based on some condition.

Syntax:

#ifdef macro_name

statement1;

statement2;

statementn;

#endif

The compiler will execute

the statements in the

block only if If

macro_name is defined.


Uses Conditional compilation directive statements are

used in cases where we need to comment out

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some code for the time being. It is also used when we want to make C

programs more portable-#ifdef LINUX

statement1;#elsestatement2;

#endif


Contains standard library functions.

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Functions available:printf()scanf()

getc()getchar()gets()putc()

putchar()puts()malloc()calloc()

fclose()fopen()fwrite()fputc()fprintf()

fseek()

fopen()fread()fscanf()fopen()ftell()

fputchar()

File handling functions20RAGHUDATHESH GP ASST PROF

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Useful functions to manipulate the strings.

unsigned int strlen(char *s)char * strcat(char *d, char *s)

int strcmpi(char *s1,char *s2)char * strrev(char *s1)char * strlwr(char *s)

char * strupr(char *s)


#includemain(){char *n1="Bangalore";char *n2="bangalore";

sman.cC BASICS


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int i,j;

printf("length of n1 :%d\n",strlen(n1));

i=strcmpi(n2,n1);if(i==0)printf("Case insensitive : Same %d\n",i);

elseprintf("Case insensitive: Different%d\n"+i);



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This library has all mathematical formulas. int abs(int x)

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double acos(double x) double asin(double x) double atan(double x) double exp(double x)

double fabs(double x) double floor(double x) double ceil(double x) double log(double x)

double pow(double x,double y) double atof(char *s) int atoi(char *s)

Similarly cos, sin

and tan functions


mat.c#includemain(int n,char* args[]){double d=13.4,f,c;int i,j,k;

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f=floor(d);c=ceil(d);printf("floor: %lf, ceil:%lf\n",f,c);

if(n>1){i=atoi(args[1]);printf("arg conversion %d\n",i); }if(n>2){

j=atoi(args[2]);k=pow(i,j);printf("%d pow %d=%d",i,j,k);}} 25RAGHUDATHESH GP ASST PROF



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Types of files I/O functions

Reading and writing unformatted text

files

Reading and writing formatted text

files

Reading and writing records


Types of File I/O

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File I/O

Text Binary

unformatted unformattedformatted


Fundamental Steps

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Open a file

Read or write

Close a file


Opening a file First step before reading or writing on to a

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file, is opening a file. The library has all the

necessary functions that allow us to work

with files. The fopen()is used to open a file.

FILE* fopen(char * filename,

char *mode) FILE is a structure defined in 4RAGHUDATHESH GP ASST PROF

Modes

Mode File exist File does not exist operations

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r Opens NULL read

w Opens Creates new overwrites

a Opens Creates new appends

r+ Opens NULL Read, writeand change

w+ Opens Creates new read,

overwritesa+ Opens Creates new Read, write

and change5RAGHUDATHESH GP ASST PROF

Unformatted reading and writingfunctions

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int getc(FILE *stream) int fgetc(FILE *stream)

int fgetc(FILE *stream)

char * fgets(char *s, int maxle

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