Call by reference :

 #include<iostream>

#include<conio.h>

using namespace std;

void swap(int &,int &);            //function declaration

int main()                         //main function

{

int a,b;

cout<<"\nenter the two numberw:\n"<<endl;

cin>>a>>b;

cout<<"\n\nbefore swaping :";

cout<<"\nA="<<a;

cout<<"\nB="<<b;

swap(a,b);                        //functiom call

  cout<<"\n\nAfter the swapping:";

cout<<"\nA="<<a;

cout<<"\nB="<<b;

getch();

return 0;

}

void swap(int &x,int &y)

{

int temp;

temp=x;

x=y;                       //function body...

y=temp;

}