Паттерн стратегия и ошибки при компиляции

#include <iostream>
using namespace std;
 
// ================================= Интерфейсы =========================================
class IFlyBehavior
{
public:
    virtual void fly() = 0;
};
// ================================ ~Интерфейсы =========================================
 
class Animal
{
public:
    Animal();
    ~Animal();
    
    IFlyBehavior *fly_behavior;
    
    void put_fly ();
    void put_sound();
    virtual void display();
};
 
Animal::Animal()
{
    cout << "Animal object was created";
}
 
Animal::~Animal(){}
 
void Animal::put_fly()
{
    fly_behavior->fly();
}
 
class duck_fly : public IFlyBehavior
{
    virtual void fly();
};
 
void duck_fly::fly()
{
    cout << "Norm fly, that i`m a duck, am i?" << endl;
}
 
class dog_fly : public IFlyBehavior
{
    virtual void fly();
};
 
void dog_fly::fly()
{
    cout << "I am not flying, that i am a dog, am i?" << endl;
}
 
class Duck : public Animal
{
public:
    Duck();
    ~Duck();
 
    virtual void display();
};
Duck::Duck()
{
    this->fly_behavior = new duck_fly ();
}
Duck::~Duck() {}
void Duck::display()
{
    cout << "I am a duck, biches" << endl;
}
 
class Dog : public Animal
{
public:
    Dog();
    ~Dog();
 
    virtual void display();
};
Dog::Dog()
{
    this->fly_behavior = new dog_fly();
}
Dog::~Dog(){}
void Dog::display()
{
        cout << "I am a dog and i can`t fly =(((" << endl;
}
 
int main()
{
    cout << "Hello World!" << endl;
 
    Duck *duck_o = new Duck();
    Dog *dog_o = new Dog();
    dog_o->display();
    dog_o->put_fly();
 
    duck_o->display();
    duck_o->put_fly();
 
    return 0;
}