Unfortunately, yes, int can vary in size depending on compiler, but if you're using a comiler on at LEAST a 32bit platform that was made in the last 10 years or so, you can assume int is 4bytes. I know for a fact you can in VS/Borlandbuilder 6+.

What the heck do they tell you to use besides an int? long?

It's not crashing on sprint_f, I believe it's wigging out on the accessing of sscanf_s.