• A function call is very important in programming.
• When we need to call a function, it is called inside a program.
• A function which is being called by the parent functions is known as called functions
• Function which is being called is known as calling function.
• A function is called by the program whenever it is needed.
• Functions are called by its name in the main program.
• We can pass parameters to the functions that are being called in the main function.

Syntax

Add(a, b) // a and b are the parameters 

Calling a function in C program

Add.c

#include <stdio.h>  
int add(int a, int b);   
void main()  
{  
  
int sum;  
int a, b;  
printf(" Enter the first and second number \n");  
scanf("%d %d", &a, &b);  
sum = add(a, b); // call add() function  
printf( "The sum of the two number is %d", sum);  
}  
int add(int n1, int n2) // pass n1 and n2 parameter  
{  
int c;  
c = n1 + n2;  
return c;  
}  

Output

Call by value

• When an single or multiple values of an argument are copied into formal parameters of a function, this type of functions is known as Call By Value.
• It does not change the value of the function`s actual parameter.

Call by Value in C programming

Call_Value.c

#include <stdio.h>  
int main()  
{  
int x = 10, y = 20;  
printf (" x = %d, y = %d from main before calling the function", x, y);  
CallValue(x, y);  
printf( "\n x = %d, y = %d from main after calling the function", x, y);  
}  
int CallValue( int x, int y)  
{  
x = x + 5;  
y = y + 5;  
printf (" \nx = %d, y = %d from modular function", x, y);  
}   

Output

Call By Reference

• As name suggests call by reference is a method, where the address of the actual argument is copied into the function call’s formal parameter.
• This type of method is known as Call by Reference.
• If we make some changes in the formal parameters, it shows the effect in the value of the actual parameter.

Call by Reference in C programming

Call_Ref.c

#include <stdio.h>  
int main()  
{  
int x = 10, y = 20;  
printf (" x = %d, y = %d from main before calling the function", x, y);  
CallValue (&x, &y);  
printf( "\n x = %d, y = %d from main after calling the function", x, y);  
}  
int CallRef( int *a, int *b)  
{  
*a = *a + 5;  
*b = *b + 5;  
printf (" \nx = %d, y = %d from modular function", *a, *b);  
}  

Output