class A {
public:
    virtual void Foo (int n = 10) {
        cout << "A::Foo, n = " << n << endl;
    }
};

class B : public A {
public:
    virtual void Foo (int n = 20) {
        cout << "B::Foo, n = " << n << endl;
    }
};

int main() {
    A * pa = new B ();
    pa->Foo ();

    return 0;
}
//(c) habrahabr//h1ppo