/*constant values are important when you want to make value remain unchanged all over the script..
Constant properties can contain only primitive values. You cannot assign an object to a constant.
Like global constants, class constants
cannot be changed once they are set. A constant property is declared with the const keyword. Constants are not prefixed with a dollar sign like regular properties.
constant values are prefixed with const keyword ..
const FLAG = 0;
public function change()
$this->FLAG = 2;
public function show()
$object = new ap();