You've corrected a few things in the program, but the logic and some other things, are still not OK.
Try the example input from your first post (or any example input you know the answer to), and SHOW the value you get when it's done. NOT just the "no number" answer, but the ACTUAL value of the ISBN numbers that the program is trying.
Add some printf()'s followed by getchar()'s, to help you see what your program is actually doing.
Or run the program in your debugger, step by step, and watch the values, to see where they are going off the rails.
First goal imo, is to get an example of a good ISBN number, to be marked as valid, by the program. Save the ? logic, until you have the easy stuff working OK.
