I think you and I are arguing semantics then. The very question "what do you mean by a string?" already indicates that you might be familiar with some of the differences between unicode and ascii, for example. In that case, I'll clarify what I mean depending on the language the candidate is most comfortable with. For example, if they plan to use C++, I might clarify that they can assume that the string is an array of chars containing letters a-z. I really just intend it as a filtering question, but someone can definitely get bonus points if they ask intelligent questions to clarify the problem.