A function can be called or
accessed by specifying its name, followed by a list of arguments enclosed in
parentheses and separated by commas. For example, add(a,b) to call a function
to add two numbers. If function call doesn’t require any arguments, any empty
pair of parentheses must follow the name of function. The arguments appearing
in the function call are referred as actual arguments. In function call, there
will be one argument for each formal argument. The value of each argument is
transferred into the function and assigned to the corresponding formal
argument.
An example
/* to find the greatest number among three
numbers.*/
#include <stdio.h>
#include<conio.h>
int greater(int x, int y) /* function definition*/
{
if(x>y)
return (x);
else
return (y);
}
void main()
{
int a, b,c,d,e;
clrscr();
printf(“Enter three
numbers”);
scanf(“%d%d%d”,&a,&b,&c);
d=greater(a,b); /* function call*/
e=greater(d,c); /* same function call again*/
printf(“The greatest number
is%d”,e);
getch();
}
Function call by value:
When actual value of variable is passed to the
function as argument, it is known as function call by value. In this call, the
value of the actual argument is copied into the function’s formal argument.
Therefore, the value of the corresponding formal argument can be altered within
the function. But, this will not change the value of the actual argument within
the calling function.
Example:
#include<stdio.h>
#include<conio.h>
void swap(int , int);
void main()
{
int a, b;
a=99; b=89;
printf(“Before function
calling, a and b are: %d\t%d”,a,b);
swap(a,b);
printf(“After function
calling, a and b are: %d\t%d”,a,b);
getch();
}
void swap(int x, int y)
{
int temp;
temp=x;
x=y;
y=temp;
printf(“The values within
functions are:%d\t%d”,x,y);
}
Output:
Before function calling, a and b
are: 99 89
The values within functions are: 89 99
After function calling, a and b are:
99 89
The above output
shows that the actual argument’s value are not changed even the value of formal
arguments are changed.
/* Program to
illustrate the function with argument and return values */
int add(int, int) ;
main()
{
int a, b, sum ;
printf (“Enter two numbers : \t”) ;
scanf (“%d%d”, &a, &b) ;
sum = add(a, b) ;
printf (“ln the sum is \t%d|, sum) ;
}
int add(int a, int b)
{
int sum ;
sum = a+b ;
return sum ;
}
Output:
Enter two numbers : 4 3 ↵
The sum is 7
Function call by Reference:
In this type of
function call, the address of variable is passed to the function as argument
instead of actual value of variable. For clear understanding of this, concept
of pointer is necessary which we will study in next chapter.
Example:
/*a program to swap the two variable’s
values*/
#include<stdio.h>
#include<conio.h>
void swap(int * , int *);
void main()
{
int a, b;
a=99; b=89;
printf(“Before swap, a and
b are: %d\t%d”,a,b);
swap(&a,&b); /*
function call by reference*/
printf(“After swap, a and
b are: %d\t%d”,a,b);
getch();
}
void swap(int *x, int *y)
{
int temp;
temp=*x; /*
here *x represent the value at address contained in variable x */
*x=*y;
*y=temp;
}
Output:
Before swap, a and b
are: 99 89
After swap, a and b are: 89 99
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