Protip: Don’t write 600 lines of code without ever testing it at all. And by testing I mean anything, manual testing included or even just compiling it or running a linter over it. Do things incrementally and verify things at each step to make sure you are not drifting off course by some faulty assumption you made near the start.
Once had a missing semi colon at the end of a c header file. The compiler kept complaining about the c file and never mentioned the header. Not all errors lead you to the right place.
Though most of the time people just don’t read them. The number of problems I have solve for people by just copy pasting the error they gave me back to them…