Error   LNK1120 2 unresolved externals

Error   LNK2019 unresolved external symbol "public: __cdecl GameWindow::GameWindow(void)" (??0GameWindow@@QEAA@XZ) referenced in function "public: __cdecl Game::Game(void)" (??0Game@@QEAA@XZ)

Error   LNK2019 unresolved external symbol "public: __cdecl GameWindow::~GameWindow(void)" (??1GameWindow@@QEAA@XZ) referenced in function "public: __cdecl Game::~Game(void)" (??1Game@@QEAA@XZ)

#pragma once

class GameWindow
{
public:

    GameWindow();
    ~GameWindow();
};

#include "GameWindow.h"

GameWindow::GameWindow()
{
}

GameWindow::~GameWindow()
{
}

#pragma once

#include "GameWindow.h"

class Game
{
public:

    Game();
    ~Game();

private:

    GameWindow window;
};

#include "Game.h"

Game::Game()
{
}

Game::~Game()
{
}

#include "Game.h"

int main(int argc, char* argv[])
{
    Game game;
    return 0;
}