Hello Harley,
Thank you for your reply, so your program first checks if any of the keys of keypad is held down for at least 20 ms and check it for 10 times. And when it made sure that a key is really held down and it is not going to bounce, it identifies the pressed key with peace of mind (without debouncing). Ok but soon I am going to implement a keypad scanning routine without debouncing as I said earlier and see the results (it will be for a user interface).

thank you