Call by value and call by reference in C Program

There are two ways to pass value or data to function in C language: call by value and call by reference. Original value is not modified in call by value but it is modified in call by reference.

Let's understand call by value and call by reference in c language one by one.

Call by value in C

In call by value, original value is not modified.

In call by value, value being passed to the function is locally stored by the function parameter in stack memory location. If you change the value of function parameter, it is changed for the current function only. It will not change the value of variable inside the caller method such as main().

Let's try to read the concept of call by value in c language by the example given below:

#include <stdio.h>  

#include <conio.h>  

void change(int num) {  

    printf("Before adding value inside function num=%d \n",num);  

    num=num+100;  

    printf("After adding value inside function num=%d \n", num);  

}  

  

int main() {  

    int x=100;  

    clrscr();  

  

    printf("Before function call x=%d \n", x);  

    change(x);//passing value in function  

    printf("After function call x=%d \n", x);  

  

    getch();  

    return 0;  

}  

Output

Before function call x=100

Before adding value inside function num=100

After adding value inside function num=200

After function call x=100

Call by reference in C

In call by reference, original value is modified because we pass reference (address).

Here, address of the value is passed in the function, so actual and formal arguments shares the same address space. Hence, value changed inside the function, is reflected inside as well as outside the function.

Note: To understand the call by reference, you must have the basic knowledge of pointers.

Let's try to understand the concept of call by reference in c language by the example given below:

 

#include <stdio.h>  

#include <conio.h>  

void change(int *num) {  

    printf("Before adding value inside function num=%d \n",*num);  

    (*num) += 100;  

    printf("After adding value inside function num=%d \n", *num);  

}  

  

int main() {  

    int x=100;  

    clrscr();  

  

    printf("Before function call x=%d \n", x);  

    change(&x);//passing reference in function  

    printf("After function call x=%d \n", x);  

  

    getch();  

    return 0;  

}  

Output

Before function call x=100

Before adding value inside function num=100

After adding value inside function num=200

After function call x=200