Hi Arran, I wanted to check whether a string from user input is null terminated before passing it to strlen or other operation which could cause undefined behaviour, but I couldn't find a way to check this. Based on my understanding, checking for null terminator, I would need to know the length of the string then check whether the last character of the string is null terminator. I have read that sizeof operator operates at compile time, so this could not work a string that a user passes. If I tried to find the string length using a loop that will also rely on the null terminator at the end. I don't know any other operators/functions that could find out the length of a string. In this case, how could I make sure a user entered string is null terminated?