This file defines is_even twice, with two different (and disagreeing) implementations – one is correct, one
has its condition backwards. C’s one-definition rule means a function may be defined exactly once per program;
having two, even if one were correct, is a compile error regardless of which one you’d actually want to call.
Submit as-is, read the “redefinition of is_even” error, then fix the file so it contains exactly one definition
of is_even – the correct one. This is the single-file version of the bug real header-based projects avoid by
keeping function bodies out of headers entirely (as covered in the lesson): if a body lived in a header and two
.c files included it, you’d get this exact error the moment both were compiled together.