Swaping value of variable A and B Through Friend Function in Classes

#include <iostream>

using namespace std;

class B;

class A

{int a;

public:

void set_val (int x ){

a=x;}

friend void swap1(A,B);};

class B{

int b;

public:

friend void swap1 (A,B);

void set_val (int y ){

b=y;}};

void  swap1 (A obj1, B obj2){

int temp;

temp =obj1.a  ;

obj1.a=obj2.b;

obj2.b = temp;

cout << "The value of a :"<<  obj1.a  << endl;

cout <<  "The value of b :"<< obj2.b  << endl;}

int main(){

A obj;

B o;

obj.set_val (5);

o.set_val(2);

swap1 (obj,o);

return 0;} 

Output: