$$

[seanpaulcail]

what is the "$$" for?

foreach ($cart as $isbn => $qty)
    {
      if($$isbn=="0")
        unset($cart[$isbn]);
      else 
        $cart[$isbn] = $$isbn;
    }

Thanks

[Jedi_Legend]

It's a variable variable.

[yelvington]

Read the section in the front of the manual that explains variables. The double-dollar-sign is used for referencing variable variables -- which are variables whose operative name is not know until runtime.