cpp-program-design-template.cpp

#include <iostream>

class Exhibit;
class Season;

class Zoo {
public:
    Zoo();
    virtual ~Zoo();

    Exhibit* habitat;
};

enum class ANIMAL { ELEPHANT, POLAR_BEAR };

class Exhibit {
public:
    Exhibit();
    virtual ~Exhibit();

    void update_display();

    Season* calendar;
    ANIMAL animal;
};

class Season {
public:
    Season() {}
    virtual ~Season() {}
    virtual Season* end_season (Exhibit*) = 0;
    virtual ANIMAL get_animal () = 0;
};

class Summer : public Season {
public:
    Summer() {}
    Season* end_season (Exhibit*);
    ANIMAL get_animal () { return ANIMAL::ELEPHANT; }
};

class Winter : public Season {
public:
    Winter() {}
    Season* end_season (Exhibit*);
    ANIMAL get_animal () { return ANIMAL::POLAR_BEAR; }
};


Zoo::Zoo() { habitat = new Exhibit(); }
Zoo::~Zoo() { delete habitat; }

Exhibit::Exhibit() { calendar = new Summer(); }
Exhibit::~Exhibit() { delete calendar; }

Season* Summer::end_season(Exhibit* display) {
    return new Winter();
}

Season* Winter::end_season(Exhibit* display) {
    return new Summer();
}

void Exhibit::update_display() {
    Season* date = nullptr;
    if (date = calendar->end_season(this)) {
        animal = date->get_animal();

        delete calendar;
        calendar = date;
    }
}


int main(int argc, char *argv[])
{
    Zoo zoo;
    zoo.habitat->update_display();
    if (zoo.habitat->animal == ANIMAL::ELEPHANT)
        std::cout << "Elephant";
    if (zoo.habitat->animal == ANIMAL::POLAR_BEAR)
        std::cout << "Polar Bear";
    std::cout << std::endl;

    (zoo.habitat)->update_display();
    if (zoo.habitat->animal == ANIMAL::ELEPHANT)
        std::cout << "Elephant";
    if (zoo.habitat->animal == ANIMAL::POLAR_BEAR)
        std::cout << "Polar Bear";
    std::cout << std::endl;

    return 0;
}

// will print:
//
// Polar Bear
// Elephant