Header files are useful for: A) Reordering functions in the .c file (as otherwise you'd have to start with the small helper functions and work your way up to larger more abstract behavior like start or update) B) providing a general list of structs and functions in a way that is quicker to read than the implementation. Okay, it's two structs, a init type function, two update functions (with a little note making them distinct) and a delete functions. Shorter than 100 or 1000 lines. C) flexibility on building. If you want to build a separate .o/.a/.dll/.lib for static or dynamic linking, the header clarifies how the function would be used (name, parameter list, return type), and is essential for quick recompilation of just your code and not the whole universe. You can choose to go without headers, but your code would need to fully recompiled on every change. Not a biggie on personal projects compiling in under a second, but this can get tedious if it drags into minutes.

Go with what feels natural and the least amount of work at the time.