How do I temporary change variables and revert it back

Good day, C2 community!

Say, I have a RPG Hero with stats: Atk, Def, and so on. And a Hero have an item that can be activated and deactivated at any time by pressing the button.

I need to do the following: when an item is Active, the Hero have temporal stats changes: +2Atk/+1Def and so on, and when item is Inactive, the Hero have its initial stats.

I've tried to use "while" loop:

While [item is Active] Atk = initial Atk + bonus[/code:2xgic75x]
and System-Compare Values event:
   [code:2xgic75x]itemIsActive = 1
   Atk = initial Atk + bonus[/code:2xgic75x]
but I get the same result: in every tick Atk increases at "bonus" value. I understand why it happens, but this is not what I need 
So, please help me. Thank you.

your second approach is fine. Just add a condition system > trigger once while true

fm4fanAT, thank you very much! It works fine now. As I understand, I have to do the same thing to remove temporary effect:

itemIsActive = 0
Trigger once
   Atk = initial Atk - bonus[/code:2ug5v6st]
Correct?

correct

but in this case

itemIsActive = 0

Trigger once

Atk = initial Atk

You can also use only 2 variables and get rid of the "initial Atk". Then you would do Atk = Atk - bonus to get back to normal