Benim class = $ MyNumber dışında global bir değişken var;

How do I declare this as a property in myClass?
For every method in my class, this is what I do:

class myClass() {

    private function foo() {
         $privateNumber = $GLOBALS['MyNumber'];
    }

}

I want this

class myClass() {

    //What goes here?
    var $classNumber = ???//the global $MyNumber;

    private function foo() {
         $privateNumber = $this->classNumber;
    }

}

EDIT: I want to create a variable based on the global $MyNumber but
modified before using it in the methods

; var $ classNumber = global $ MyNumber + 100: gibi bir şey