C++ mutual class dependency

Question

I am writing a card game in C++. I have a player class, which handles the actions (i.e. selecting a card to lay). If the player is a human, it will use a GUI class<

Answer 1

Sometimes it is not necessary to include header for a class in order to use it. For example, if you only use pointer or reference to a class, you can forward-declare it: instead of

#include "player.h"
class AI
{
  std::vector pl;
};

you can write

class player;
class AI
{
  std::vector pl;
};