Polymorphism

#include "grade.h"
#include <iostream>
#include <vector>
#include <iostream>
using namespace std;


class Animal
{
public:
    virtual void sound() { cout << "i'm an animal" << endl;}
};

class People : public Animal
{
public:
    void sound() { cout << "I'm a people" << endl;}
    void loving() { cout << "I can love" << endl;}
};

int main()
{
    vector<Animal*> world;
    Animal* animal = new Animal();
    Animal* people = new People();

    animal->sound();    // i'm an animal
    people->sound();    // i'm a people

    /*CANNOT*/
    // people->loving(); // because i'm an animal, i cannot love :(

    /* no error: because both animal and people are "animal" */
    world.push_back(animal);
    world.push_back(people);

    People* realPeople = new People();
    realPeople->sound();
    realPeople->loving();       // Ah, now i can love :x
    world.push_back(realPeople);
    //world[2]->loving(); // NOOOO, I cannot love :( because everyone now sees me as an real animal :((

}