Lecture 5 examples, including inheritance, public, private, protected, and new

L5-examples-BIT2400.cpp

//Lecture 5 - BIT2400 
//Example 3 - Inheritance & protected
//Exercise: Watch https://www.youtube.com/watch?v=jsNE1yGItx0 and
//make bullets have a different hit value depending on speed 

#include <iostream>
#include <string>

using namespace std; //this is OK for our class only

class Player; //forward declaration (because I need it inside of Enemy and it doesn't exist yet)

class Enemy {
private:
	int hp;
	string name;
protected:			//note that now attackPoints are protected instead of private (so they are inherited)
	int attackPoints;
public:
	void hit(Player& p);
	Enemy() {
		hp = 0;
		name = "Dr No";
		attackPoints = 10;
	}
};

class Player {
private:
	int hp;

public:
	string name;
	int getHp();	//this is similar to the prototype declaration of a function
	void gotAttacked(int points);

	friend void resetHp(Player& p);
	friend void Enemy::hit(Player& p); //I could make the whole class friend
	friend class Bullet;	//  Friendship is a non-transitive relationship, meaning that it does not pass from one class to another through inheritance.
	Player() {
		name = "Gene Ric Name";
		hp = 100; //don't leave uninitialized variables!
	}

};

class Bullet : public Enemy { //not to be confused with other public enemies
private:
	float speed;
	static int qtyBulletsShot;

public:
	float getSpeed() {
		return speed;
	}
	void shoot();

	void hit(Player& p);

	Bullet(float s) {
		speed = s;
		qtyBulletsShot++;
	}
	~Bullet() {
		cout << "-bullet destroyed-" << endl;
	}
	static int howManyBullets() {		//this function doesn't belong technically to the object but to the class
		return qtyBulletsShot;
	}
};


int Player::getHp() {	//this "getter" reads the private health points and shares it, but doesn't allow others to write it
	return hp;
}

void Player::gotAttacked(int points) {	//this attack function is an indirect way of modifying hp
	if ((*this).getHp() > 0) {			//note the parenthesis around the *
		this->hp = this->hp - points;	//a way to avoid the (* ) is to use ->
	}
	return;
}

void Enemy::hit(Player& p) {
	p.hp -= attackPoints;

}

void resetHp(Player& p) {
	p.hp = 100;
}

void Bullet::shoot() {
	this->speed = 3.14;		//a great place to decide how fast bullets will go
}

void Bullet::hit(Player& p) {

	//you need to fill in code here
	return;
}


int Bullet::qtyBulletsShot = 0; //I need to initialize static variables before using them


int main() {
	Player p1;
	Enemy e1;

	cout << "The name of the Player 1 assigned by the constructor was: " << p1.name;
	p1.name = "PlayerOgre12345";
	cout << ", but it changed to" << p1.name << endl << endl;
	cout << "Health Points cannot be accessed directly, only through the getter. Now getHp() gives: " << p1.getHp() << endl << endl;
	p1.gotAttacked(5);
	cout << "After the attack, health is: " << p1.getHp() << endl  << endl;
	resetHp(p1);
	cout << "After resetting HP: " << p1.getHp() << endl << endl;
	e1.hit(p1);
	cout << "Enemy hits p1, so now HP is: " << p1.getHp()  << endl << endl;

	for (int i = 0; i < 5; i++) {
		Bullet* b = new Bullet(2.39);
		b->hit(p1);
		cout << "Shooting bullet number " << i << ", leaving p1 with health: " << p1.getHp() << endl;
		delete b;
	}
	cout << "Total of bullets shot is: " << Bullet::howManyBullets() << endl << endl;
	return 0;
}