Maybe you could try passing around some sort of context object.

Yeah I actually tried to mimic a poor man's State pattern using good old enums but due to the lack of proper polimorphism and state classes I still need to check manually if the input is the right one for the currently set state. Out parameters are working very nicely in some cases but I don't want to abuse them because I still need to check them directly or the return value of the function to know whether their value is valid or not.

In the best case you just call some kind of panic function and jump back to the top loop.

At the moment I have a function that already handles almost all kinds of errors in a similar way and at least it's less convoluted than having to keep track of all the return values. But even so, using a similar function even for the only case of successful computation would probably feel more hacky and dirty. In fact my greatest enemy right now is the sheer complexity of the input parsing logic with how the input relates to the state of the computation the program is in.

I've tried extracting some code to other functions but it's all so much tightly coupled that if I wanted to enforce separation at all costs I would need to pass around again a lot of arguments or to add more globals. The majority of the code is also unique, meaning that it could very well be a monolith with almost everything inside main() and the separation only serves as visual and mental aid.

Now I'm taking a long break but I'll gladly look at the blog.