Call by Value and Call by Reference in C

Call by Value

Call by Value is a method of passing arguments that are used to a function and copies the actual value of an argument into the formal parameter of the function. In this case, changes made to the parameter inside the function do not affect the argument.

Example:

#include<stdio.h>
#include<conio.h>
void main()
{
int x=25, y=10;
void add(int p, int q);
clrscr();
printf("Before function call x=%d y=%d",x,y);
add(x,y);
printf("After function call x=%d y=%d",x,y);
getch();
}
void add(int p, int q)
{
p=p+10;
q=q+10;
printf("Inside the function call x=%d y=%d",x,y);
}

Call by Reference:

It permits us to pass parameters to the function by reference. When we pass the arguments by reference, the formal arguments in the called function become aliases to the actual arguments in the calling function which means when the function is working with its arguments.

Example:

#include<stdio.h>
#include<conio.h>
void main()
{
int x=25, y=10;
void add(int p, int y);
clrscr();
printf("Before function call x=%d y=%d",x,y);
add(&x,&y);
printf("After function call x=%d y=%d",x,y);
getch();
}
void add(int *x,int *y)
{
*x=*x+10;
*y=*y+10;
printf("Inside the function call x=%d y=%d",*x,*y);
}

Actual Arguments:

The arguments listed in the function calling statement that is called Actual Arguments.
Example:

Formal Arguments:

The arguments used in the function declaration that is called Formal Arguments.
Example:

We can Difference between Call by Value and Call by Reference given below:

Call by Value vs Call by Reference: