C FUNCTION
WHAT IS C FUNCTION?
• A large C program is divided into basic building
blocks called C function. C function contains
set of instructions enclosed by “{ }” which
performs specific operation in a C program.
Actually, Collection of these functions creates
a C program.
USES OF C FUNCTIONS:
• C functions are used to avoid rewriting same
logic/code again and again in a program.
• There is no limit in calling C functions to make use of
same functionality wherever required.
• We can call functions any number of times in a
program and from any place in a program.
• A large C program can easily be tracked when it is
divided into functions.
• The core concept of C functions are, re-usability,
dividing a big task into small pieces to achieve the
functionality and to improve understandability of very
large C programs.
C FUNCTION DECLARATION, FUNCTION CALL
AND FUNCTION DEFINITION:
• There are 3 aspects in each C function. They
are,
• Function declaration or prototype –
This informs compiler about the function
name, function parameters and return value’s
data type.
• Function call – This calls the actual function
• Function definition – This contains all the
statements to be executed.
Syntax of Functions
The syntax of function can be divided into 3
aspects:
Function Declaration
Function Definition
Function Calls
Function Declarations
Syntax:
return_type name_of_the_function (parameter_1, parameter_2);
Example
int sum(int a, int b); // Function declaration with parameter names
int sum(int , int); // Function declaration without parameter names
Note: A function in C must always be declared globally before calling it.
Function Definition
return_type function_name (para1_type para1_name, para2_type para2_name)
{
// body of the function
}
Example
int sum(int a, int b); // Function declaration with parameter names
int sum(int , int); // Function declaration without parameter names
C functions aspects syntax
Re t urn _t yp e
function_name
(arguments list)
function definition { Body of function; }
function_name
function call (arguments list);
re t urn _typ e
function_name
function declaration (argument list);
SIMPLE EXAMPLE PROGRAM FOR C
FUNCTION
• As you know, functions should be declared
and defined before calling in a C program.
• In the below program, function “square” is
called from main function.
• The value of “m” is passed as argument to the
function “square”. This value is multiplied by
itself in this function and multiplied value “p”
is returned to main function from function
“square”.
Conti..
#include<stdio.h>
// function prototype, also called function declaration
float square ( float x );
// main function, program starts from here
int main( )
{
float m, n ;
printf ( "\nEnter some number for finding square \n");
scanf ( "%f", &m ) ;
// function call
n = square ( m ) ;
printf ( "\nSquare of the given number %f is %f",m,n );
}
float square ( float x ) // function definition
{
float p ;
p=x*x;
return ( p ) ;
}
Output
Enter some number for finding square
2
Square of the given number 2.000000 is
4.000000
HOW TO CALL C FUNCTIONS IN A
PROGRAM
• There are two ways that a C function can be
called from a program.
• Call by value
• Call by reference
CALL BY VALUE
• In call by value method, the value of the variable is
passed to the function as parameter.
• The value of the actual parameter can not be modified
by formal parameter.
• Different Memory is allocated for both actual and
formal parameters. Because, value of actual parameter
is copied to formal parameter.
• Note:
• Actual parameter – This is the argument which is used
in function call.
• Formal parameter – This is the argument which is used
in function definition
EXAMPLE PROGRAM FOR C FUNCTION
(USING CALL BY VALUE):
• In this program, the values of the variables
“m” and “n” are passed to the function
“swap”.
• These values are copied to formal parameters
“a” and “b” in swap function and used.
Conti..
#include<stdio.h>
// function prototype, also called function declaration
void swap(int a, int b);
int main()
{
int m = 22, n = 44;
// calling swap function by value
printf(" values before swap m = %d \nand n = %d", m, n);
swap(m, n);
}
void swap(int a, int b)
{
int tmp;
tmp = a;
a = b;
b = tmp;
printf(" \nvalues after swap m = %d\n and n = %d", a, b);
}
Output
• values before swap m = 22
and n = 44
values after swap m = 44
and n = 22
CALL BY REFERENCE:
• In call by reference method, the address of the
variable is passed to the function as
parameter.
• The value of the actual parameter can be
modified by formal parameter.
• Same memory is used for both actual and
formal parameters since only address is used
by both parameters.
EXAMPLE PROGRAM FOR C FUNCTION
(USING CALL BY REFERENCE)
• In this program, the address of the variables “m”
and “n” are passed to the function “swap”.
• These values are not copied to formal parameters
“a” and “b” in swap function.
• Because, they are just holding the address of
those variables.
• This address is used to access and change the
values of the variables.
•
Conti..
#include<stdio.h>
// function prototype, also called function declaration
void swap(int *a, int *b);
int main()
{
int m = 22, n = 44;
// calling swap function by reference
printf("values before swap m = %d \n and n = %d",m,n);
swap(&m, &n);
}
void swap(int *a, int *b)
{
int tmp;
tmp = *a;
*a = *b;
*b = tmp;
printf("\n values after swap a = %d \nand b = %d", *a, *b);
}
Output
• values before swap m = 22
• and n = 44
values after swap a = 44
