After a few disappointing responses to better questions, interviewer decides to give a "freebie" and asks for a function that determines whether an integer is odd or even.
Candidate produces something that loops from 0 to the provided integer, incrementing two separate counters, then comparing them at the end.
Interviewer manages to stammer out something like "are you sure there isn't a more efficient way to solve this?"
Guy furrows his brow for a few minutes more, then a light bulb of sorts goes on, and he declares "Of course! ..."
"... I only need one counter!"
Though perhaps, if they were more competent as a programmer, they would skip decimal math altogether and use the ol' bitwise operator trick.
char s[32];
sprintf(s, "%d", n);
char c = s[strlen(s) - 1];
return c == '0' || c == '2' || c == '4' || c == '6' || c == '8';