Call by value vs. Call by reference in C programming

Published on : 3rd Oct 2021

Call by value :
When a function is called by value of variables, the process is known as call by value.
Source Code :
#include <stdio.h>

int add(int num1, int num2)
{
	return num1 + num2; 	
}

int main(int argc, char** argv)
{
	int num1 = 10, num2 = 20; 
	int res = add(num1, num2); // call by value
	printf("Addition = %d", res);
	return 0;
}
Output :
Addition = 30
Call by reference or call by address :
When a function is called by addresses of variables, the process is known as call by address or call by reference. 
Source Code :
#include <stdio.h>

void swap(int *x, int *y)
{
	int temp = *x;
	*x = *y;
	*y = temp;
}

int main(int argc, char** argv)
{
	int num1 = 10, num2 = 20; 
	printf("Before call, num1  = %d and num2 = %d\n", num1, num2);
	swap(&num1, &num2); // call by reference
	printf("After call, num1  = %d and num2 = %d\n", num1, num2);
	return 0;
}
Output :
Before call, num1  = 10 and num2 = 20
After call, num1  = 20 and num2 = 10