Forward declaring structs in C.c

//
//  main.c
//

#include <stdio.h>
#include "Game.h"

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



//
//  Game.h
//

#ifndef Forward_Game_h
#define Forward_Game_h



typedef struct Game Game;


Game * NewGame();
void RunGame(Game * game);


#endif





//
//  Game.c
//

#include <string.h>
#include <stdlib.h>
#include <stdio.h>

#include "Game.h"
#include "Manager.h"


struct Game {
    int score;
    Manager * manager;
};



Game * NewGame()
{
    Game * game = (Game *)calloc(sizeof(Game), 1);
    game->manager = NewManager();
    return game;
}


void RunGame(Game * game)
{
    UseManager(game->manager);
    printf("Game over.\n");
}





//
//  Manager.h
//

#ifndef Forward_Manager_h
#define Forward_Manager_h


typedef struct Manager Manager;


Manager * NewManager();
void UseManager(Manager * manager);

#endif





//
//  Manager.c
//

#include <string.h>
#include <stdlib.h>
#include <stdio.h>

#include "Manager.h"
#include "Game.h"


struct Manager {
    int stuff;
};


Manager * NewManager()
{
    return (Manager *)calloc(sizeof(Manager), 1);
}


void UseManager(Manager * manager)
{
    printf("Used manager.\n");
}