[ajeet_dhaliwal]

Good point, I've encountered this. Some candidates unfamiliar with the process may not even realize they want you to ask that, I didn't know when I started out and used to think a good interviewer would specify what they want, that may not be true, although it would be a nice thing to remind a candidate they can ask for clarifications not just about the question but about testing and such.

I know some interviewers may be interested in helping but it's important to note assholes exist, especially at larger companies. There can be head games and assumptions made where they needn't have been. Even when I've been hired it can feel like if I'd done it again I may not have been. Try your best but don't be too upset if it goes badly either. Similar questions often come up too, it's actually amazing how many questions there are about linked list and trees.

[bshlgrs]

I also think that it's not obvious that the interviewer is doing the wrong thing here. The claim "good programmers should always think to guard against invalid input" isn't ridiculous on the face of it: maybe checking for valid input is a sign that they're careful and methodical, and of course you want to hire careful and methodical people!

Or the other way around: I can imagine someone thinking "this person spent ages on checking for invalid input; I bet their code is always bloated and ugly".

The problem is that programmers do this one way or the other based on personal preference, not because of actual differences in ability. Once you know that, it makes less sense to care one way or the other.

[jerf]

If you think my code's checking carefully for the validity of the input makes it bloated and ugly, you just failed my interview.

[greenleafjacob]

There's a correct place for every class of input validation. The point is that you don't want multiple levels of input validation for the same thing. Most of what passes for "defensive coding" is superfluous. For example, if you are passing a pointer into a function, you don't need to reflexively null check. However, null checks are important.