Program To Use of Friend Functions in C++

#include <iostream>

using namespace std;class Square;class Rectangle {int width, height;public:int area () {return (width * height);}void convert (Square a);};class Square {friend class Rectangle;private:int side;public: Square (int a) : side(a) {}};void Rectangle::convert (Square a) { width = a.side; height = a.side;}int main () { Rectangle rect; Square sqr (4); rect.convert(sqr); cout << rect.area();return 0;}