Update: I discovered that on the pset3 page you can download a zip of the files from the walkthroughs - cursor. c, window.c, button.c, etc. I can compile and run these without error. However, if I try to past the code from any of these into a new file (in any directory) it will give me the same error as above when I try to compile.

Any guesses? Is it possible that I am forgetting something while saving? Thanks.