This question came up on Stack Exchange ; Using C, how can you write filenames dynamically using an iterative variable loop? Or in English, you want to write some stuff to a bunch of different files, and have those files named in a logical manner like file1.file, file2.file, file3.file, ... etc. The answer is pretty simple, but a bit of a mind-bender when you are first getting started. I was also pretty astonished that all of the accepted "solutions" to the problem failed to compile. This is a pretty big issue on these programming solution websites. I think the reason for the problem is there are two groups of people: There are the people who want other people to think they can fix stuff. Then there are the people who can fix stuff. The two groups, obviously, have some overlap: people who can fix stuff and who want others to know about it. But there is also a statistically significant portion of both groups that do not overlap - people who can fix stuff who don't care