That's doesn't really mean much, what are you trying to do ?
If you ever delete whatsapp your phone will remember and download it. Whatsapp might send you another activate code bits that's it
I don't use WhatsApp. But from what it says in the description in the App Store, I don't think you can use a passcode or password to lock it. There is no more log in. You will just have to lock your phone.