Function call By Value And Call By Reference

call by reference 

The call by reference method of passing arguments to a function copies the reference of an argument into the formal parameter. Inside the function, the reference is used to access the actual argument used in the call. This means that changes made to the parameter affect the passed argument.

#include <iostream>

using namespace std;

 // function declaration

void swap(int &x, int &y);

 int main () {

   // local variable declaration:

   int a = 100;

   int b = 200;

     cout << "Before swap, value of a :" << a << endl;

   cout << "Before swap, value of b :" << b << endl;

   /* calling a function to swap the values using variable reference.*/

   swap(a, b);

   cout << "After swap, value of a :" << a << endl;

   cout << "After swap, value of b :" << b << endl;

   return 0;

}

call by value

The call by value method of passing arguments to a function 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 have no effect on the argument. By default, C++ uses call by value to pass arguments.

#include <iostream>

using namespace std;

// function declaration

void swap(int x, int y);

 int main () {

   // local variable declaration:

   int a = 100;

   int b = 200;

      cout << "Before swap, value of a :" << a << endl;

   cout << "Before swap, value of b :" << b << endl;

   // calling a function to swap the values.

   swap(a, b);

   cout << "After swap, value of a :" << a << endl;

   cout << "After swap, value of b :" << b << endl;

   return 0;

}