How would I use aggregation with this class (beginner code)? - c++

Question

I would like to understand aggregation so I tried making a simple test code, but it doesn't work in my compiler, sometimes it works online.
code for main:
#include <iostream>
#include <string>
#include "player.h"
#include "game.h"
using namespace std;
int main(){
game game;
game.playGame();
return 0;
}
code for game.cpp:
#include "game.h"
#include "player.h"
game::game(){
player.setBalance(0);
}
void game::playGame(){
cout << "playing game." ; //just for debugging
}
code for game.h:
#ifndef GAME
#define GAME
#include <iostream>
using namespace std;
class game{
private:
player player;
public:
game();
void playGame();
};
#endif
code for player.cpp:
#include "player.h"
player::player(){
balance = 0;
}
player::player(int theBalance){
balance = theBalance;
}
int player::getBalance(){
return balance;
}
void player::setBalance(int theBalance){
balance = theBalance;
}
code for player.h:
#ifndef PLAYER // used on headers
#define PLAYER
class player{
private:
int balance;
public:
player();
player(int);
int getBalance();
void setBalance(int);
};
#endif
I think the problem is probably on the headers.
the error I get is:
In file included from main.cpp:5:0:
game.h:10:12: error: declaration of 'player game::player' [-fpermissive]
player player;
In file included from main.cpp:4:0:
player.h:5:7: error: changes meaning of 'player' from 'class player' [-fpermissive]
class player{
^~~~~~

Answer 1

I think that the problem is in class game, because it doesn't know a class player, use forward declaration or just write #include "player.h" in game.h