#include <iostream>
using namespace std;

class B;
class A {
    private:
      int x;
    public:
      A()
        {
            x=10;
        }
      friend int sub(A, B);
};

class B {
    private:
       int y;
    public:
       B()
        {
            y=2;
        }
       friend int sub(A , B);
};

int sub(A objectA, B objectB)
{
   return (objectA.x - objectB.y);
}

int main()
{
    A objectA;
    B objectB;
    cout<<"Substraction: "<< sub(objectA, objectB);
    return 0;
}


================================output============================
Substraction: 8