In current directory, All C header files (*.h) don't include the preprocessor macro
I'm going to second @kaylum's advice and also not give you the whole thing, but here is some pseudocode that might set you on the right path
for each file in the directory if filename doesn't end with .h continue open the file store its contents in a variable create the header guard by taking the filename, removing the '.', and replacing it with a '_' create new contents = headerGuard + contents + "\n#endif" write file back out to the same name
Each of these things should be answerable with a quick google/stack overflow search, and if you can't figure out any of those parts, a specific stack overflow question about that bit would be better suited for this site. And here is one link to a relevant question to get you started.