BehemothPhoenix

Basically, I have to write a program for school, in which I have to determine whether a user inputted value is prime or not. I also have to write another program determining what factors of an inputted value are prime. I've tried everything (and we can't use the math.h library). I'm really not too sure what to do, and any help you could give me would be greatly appreciated!!

Edit: I don't really need a whole program, just an idea of where to start.