I dont think Sorensen meant to literally put a '?' after isdigit() in your code. He meant it as a response to your question as to what is the purpose of isdigit(). Think about it a little. Or even better, use one of those bizarre things called 'search engines.' I've heard that the one called 'www.google.com' is pretty good. Kinda high-tech though. Alternatively, it is included in the functions section of this site.
