public $for_sale = true; public function __construct($color = null) { if ($color) { $this->color = $color; } } public function add_room() { $this->rooms++; } public function sell() { $this->for_sale = false; } } $house = new House('red'); $house->add_room(); $house->add_room(); echo "This {$house->color} house has {$house->rooms} rooms. "; echo $house->for_sale ? "It is for sale." : "It is not for sale."; echo "<br>"; $house2 = new House(); $house2->add_room(); $house2->add_room(); $house2->add_room(); $house2->add_room(); $house2->add_room(); $house2->sell(); echo "This {$house2->color} house2 has {$house2->rooms} rooms. "; echo $house2->for_sale ? "It is for sale." : "It is not for sale.";