C++ error C2227: left of '->looseHealth' must point to class/struct/union/generic type

Question

So the problem here is that a Player requires a Card, therefore, the Card needs to be declared on top of the Player class. Further on my Card class uses a function that needs a Player pointer parameter. To remove other errors I used a forward declaration above the Card class to make the Player class visible. I'm also using a pointer to a Player in the attackEnemy function parameters as the size of the object cannot be known at that point with only a forward declaration. When i try to invoke a function from the passed Player pointer in the attackEnemy function inside the Card I get a compile error. The error is error C2227: left of '->looseHealth' must point to class/struct/union/generic type.

This is the program:

#include "stdafx.h"
#include <iostream>
using namespace std;
class Player;
class Card {
private:
    int attack;
public:
    Card() {
        this->attack = 2;
    }

    void attackEnemy(Player* i) {
        i->looseHealth(this->attack); //error is here
    }
};

class Player {
private:
    string name;
    int health;
    Card* playersCard;
public:
    Player(string name) {
        playersCard = new Card();
        this->name = name;
    }

    void looseHealth(int x) {
        cout << "lost health -" << x << " points" << endl;
        health -= x;
    }
};

int main()
{
    Card* opponedsCard = new Card();
    Player* player1 = new Player("player 1");
    opponedsCard->attackEnemy(player1);
    return 0;
}

Answer 1

The attackEnemy uses a incomplete type Player, which is forward declared.

Just declare void attackEnemy(Player* i); in Card class and move

void attackEnemy(Player* i) {
        i->looseHealth(this->attack); //error is here
    }

After definition of Player class

void Card::attackEnemy(Player* i) {
        i->looseHealth(this->attack); //error is here
    }