Global Variable?

Hello, 
i'm new here and i find it is hard to find an answer at google due to my lacks of grammar or i don't even know what i'm gonna search. I've been thinking this over and over and also with practices but i got nothing. so, i want to ask everybody in this forum about this "global variable or not" thing.

i have a controller, i called it A_Controller and it is look like this:

PHP Code:

class A_Controller extends CI_Controller {

  var $global = 0;

  public function __construct(){
    parent::__construct();
  }

  public function setGlobal($value){
    $this->global = $value;
  }

  public function index(){
    echo $this->global;
  }

} 


what i want to approach is, when i access /A_Controller/setGlobal/1000 the global variable is set. and i want to see its value at /A_Controller/index. but, i always got the global is 0.