#include <iostream>
using namespace std;

class Animal
{
public:
    virtual void sound() = 0;
};

class Dog : public Animal
{
public:
    void sound()
    {
        cout << "Bark" << endl;
    }
};

class Cat : public Animal
{
public:
    void sound()
    {
        cout << "Meow" << endl;
    }
};

int main()
{
    Animal *a;
    Dog d;
    Cat c;
    a = &d;
    a->sound();
    a = &c;
    a->sound();
    return 0;
}