Do I need to explicitly handle negative numbers or zero when summing squared digits?

Question

I recently had a test in my class. One of the problems was the following:

Given a number n, write a function in C/C++ that returns the su

Answer 1

I wouldn't argue about whether the original or the modern definition of '%' is better but anyone who writes two return statement into such a short function shouldn't teach C programming at all. Extra return is a goto statement and we don't use goto in C. Furthermore the code without the zero check would have the same result, extra return made it harder to read.