#include <iostream> using namespace std; 

class A 
{ public:
    A(int a);
    int whata();
private:
    int mya;
};

A::A(int a) : mya(a) {}

int A::whata() { return mya; }


class B: public A 
{ public:
    B(int a);
    int whatb();
private:
    int myb;
};

B::B(int b) :A(2*b), myb(b) { }

int B::whatb() { return myb; }

void fA(A a) {
    cout << "\nPara A:" << a.whata() << "\n";
}

void fB(B a) {
    cout << "\nPara B:" << a.whata() << "\n";
}


void main() 
{
    A a(1);
    B b(2);
    cout << " a:" << a.whata() << endl;
    cout << " b:" << b.whatb() << " b's a:" << b.whata() << "\n\n";
    fA(a);
    fA(b); // However, if B inherites A in private, this call is not allowed.
//  fB(a); // This is not allowed, even though whatb() is not used.
    fB(b);
    a = b; // B is an A with some extra properties.
//  b = a; // This is not allowed.
}