Passing argument to a function by value is also know as call by value. This method of passing arguments to a function copies the original value of argument into the formal parameter of a function. In other words if we change parameter which are given inside a function posses no effect on the argument .

C language support by default call by value for passing arguments.

Below is the example of how to pass argument by value.

 // function definition for swapping two  integer type values a and b
void swap(int a, int b) 
{      

   int t;

   t = a;                                    //  t variable save the value of  a
   a = b;                                    // we put value of b into a 
   b = t;                                     // put t into b 

   return;
}

Now, we call the function swap() by passing original values . 

#include <stdio.h>


void swap(int a, int b);    

int main () {


   int x = 5;   //    local variable definition 
   int y = 6;

   printf("Before swap, value of x : %d\n", x );
   printf("Before swap, value of y : %d\n", y );

   //  Now we are calling a function to swap two values 

    swap(x, y);

   printf("After swap value of x : %d\n", x );
   printf("After swap value of y : %d\n", y );

   return 0;
}


Before swap value of x :5
Before swap value of y :6
After swap value of x :5
After swap value of y :6

This shows that if we change parameter which are given inside a function posses no effect on the argument .