#include <iostream>
using namespace std;

class A
{
public:
    virtual void show()
    {
        cout << "Class A" << endl;
    }
};

class B : public A
{
public:
    void show()
    {
        cout << "Class B" << endl;
    }
};

int main()
{
    A *p;
    A a;
    B b;
    p = &a;
    p->show();
    p = &b;
    p->show();
    return 0;
}