ООП Дружественные Функции, Операторы.

#include <iostream.h> 
#include <string.h> 
class chisla 
{ 
      
public: 
   double x,y,z;
   void pplus(void)
   { 
      z=x-y;
      cout<<"x-y = "<<z<<endl;
      getchar();
    };   
}; 
int main(void) 
{ 
   chisla plus; 
   cout<<"vvedite x = "<<endl;
   cin>>plus.x;
   cout<<endl;
   cout<<"vvedite y = "<<endl;
   cin>>plus.y;
   cout<<endl; 
   plus.pplus();
   getchar();
}

#include <iostream>
using namespace std;
 
class my_int{
public:
    my_int(int _i = 0):i(_i){}
    my_int(const my_int & rhs){
        *this = rhs;
    }
    my_int &operator = (const my_int &rhs){
        if(this != &rhs){
            i = rhs.i;
        }
        return *this;
    }
 
    my_int &operator = (int value){
        i = value;
        return *this;
    }
    my_int operator + (const my_int &rhs) const {
        my_int buff(*this);
        buff.i += rhs.i;
        return buff;
 
    }
 
    my_int &operator +=(const my_int &rhs){
        i += rhs.i;
        return *this;
    }
 
    friend ostream &operator << (ostream &lhs, const my_int &rhs);
    friend istream &operator >> (istream &lhs, my_int &rhs);
private:
    int i;
};
 
ostream &operator << (ostream &lhs, const my_int &rhs){
    return lhs << rhs.i;
}
istream &operator >> (istream &lhs, my_int &rhs){
    return lhs >> rhs.i;
}
int main ( )
{
    my_int i = 10;
    my_int j = 15;
    my_int c = 5;
 
    cout << i + j << endl;
    c += i;
    cout << c << endl;
 
    c = i + j;
    cout << c << endl;
 
    cout << i << endl;
    i = c;
    cout << i << endl;
    return 0;
}

#include <vcl>
#pragma hdrstop
#include <iostream>
 
using namespace std;
 
class building {
    int rooms, floors, area;
    public: void set_rooms (int num);
            int get_rooms ();
            friend int mult_two (building b1);
 
};
 
//Производный класс.
class house: public building {
    int bedrooms, baths;
    public: void set_bedrooms (int num);
            int get_bedrooms ();
};
 
void building::set_rooms(int num) {
    rooms=num;
}
 
void house::set_bedrooms(int num) {
    bedrooms=num;
}
 
int house::get_bedrooms() {
    return bedrooms;
}
 
int building::get_rooms() {
    return rooms;
}
 
int mult_two (building b1) {
    return 2*b1.rooms;
}
//---------------------------------------------------------------------------
 
#pragma argsused
int _tmain(int argc, _TCHAR* argv[])
{
    system ("title Temp");
    building b;
    b.set_rooms(25);
    cout <<mult_two (b)<<'\n';
    house h2;
    h2.set_rooms(15);
    cout <<mult_two (h2)<<'\n';
    system ("pause");
    return 0;
}
//---------------------------------------------------------------------------