CodeIgniter call method from within a method in the same class

I am trying to do this code in my CodeIgniter application :

class Inventory extends Controller
{

    function current_stock()
    {
        //do something
    }

    function add_stock()
    {
        //do something-else
        ****then do function current_stock()*****
    }
}

How do I execute another method from within a second one? The approach outlined here (about extending controllers) is something of an overkill for me.

Am I missing a much easier way?