public function initGame()
    {
        $this->board = array();
        $this->last_player = null;

        for ($x=0; $x<$this->size; $x++) {
            $row = array();

            for ($y=0; $y<$this->size; $y++) {
                $row[] = null;
            }

            $this->board[] = $row;
        }

        $this->display();
    }