循环运行时错误

我用c++做了一个非常简单的游戏。大部分工作正常，但每当我尝试重玩游戏时，该值都不会重置，而是从我上次离开的地方继续，这不是我希望它发生的情况。比如说，在我第一次尝试时，我击败了敌人，它的生命值为零，当我重试时，该值不是从 100 开始，而是从零开始。我真的想要解决这个问题。无论如何，这是我的代码("它很长)：

#include <iostream> 
#include <string>
using namespace std;
class Health{
private:
int health;
Health(const Health& cpy){
health = cpy.health;
}
public:
Health(){
health = 100;
}
void display_health(){
cout << "Health: " << health << endl;
}
Health& operator -=(int atk){
health -= atk;
return *this;
}
bool operator <(int compare){
return (health < compare);
}
bool operator >(int compare){
return !(this->operator<(compare));
}
bool operator &&(const int compare){
return (health && compare);
}
};
class Hero : public Health{
public:
void kick(){
cout << "Your kick damaged 45 health points" << endl;
}
void Punch(){
cout << "Your punch damaged 25 health points" << endl;
}
void Knife(){
cout << "Your kinfe damaged 60 health points" << endl;
}
void Tackle(){
cout << "Your tackle damaged 10 health points" << endl;
}
};
class Enemy : public Health{
public:
void Basic_hit(){
cout << "Enemy damaged you by 25 point" << endl;
}
};
int main(){
//local vaiables 
string name;
int choice;
string ply_agn = "y";
//instance
Hero hero;
Enemy enmy;
//user interface
do{ //entire game repeats
cout << "Enter you character name: ";
getline(cin, name);
cout << "Your default health is : ";
hero.display_health();
cout << endl;
do{
//user interface
cout << "0.Kick - 45" << endl;
cout << "1.Punch - 25 " << endl;
cout << "2.Kinfe -  60" << endl;
cout << "3.Tackle - 10 " << endl;
//players choice
cout << "Which move you like to chose: ";
cin >> choice;
cout << endl;
//switch function
switch (choice)
{
case 0:
hero.kick();
cout << "Enemy ";
enmy -= 45;
enmy.display_health();
break;
case 1:
hero.Punch();
cout << "Enemy ";
enmy -= 25;
enmy.display_health();
break;
case 2:
hero.Knife();
cout << "Enemy ";
enmy -= 60;
enmy.display_health();
break;
case 3:
hero.Tackle();
cout << "Enemy ";
enmy -= 10;
enmy.display_health();
break;
default:
cout << "Invalid move! Try again" << endl;
break;
}
cout << endl;
//Enemy move 
enmy.Basic_hit();
hero -= 25;
cout << "The enemy hit you with a basic hit. You recieved 25 damage" << endl;
cout << "Your ";
hero.display_health();
cout << endl;
} while (enmy > 0);
//winning condition
if (enmy < 0 && hero > 0) {
cout << "You won" << endl;
}
else if (hero < 0 && enmy > 0){
cout << "You lose" << endl;
}
else if (hero < 0 && enmy < 0){
cout << "This game is a draw" << endl;
}
} while (ply_agn == "y"); //This is where I think is messing up the game
//repeating condition
cout << "Would you like to play again: ";
cin >> ply_agn;
system("pause");
return 0;
}

谢谢你的时间