> You do realize it returns 1 for an empty string right? I mean it doesn't have any digits in it... Yes, and that was deliberate on my part, as it meets my exp

> You do realize it returns 1 for an empty string right? I mean it doesn't have any digits in it... Yes, and that was deliberate on my part, as it meets my expectation of what such a function should do in this edge case. The problem statement was "Set boolean b to true if string s contains only characters in range '0'..'9', false otherwise." To my mind, the question "is every character in the string a digit" should be equivalent to "are there any non-digits in the string" (with the answer inverted, of course). Returning 0 (false) for the empty string makes those questions not equivalent. It makes the empty string a special case. Of course the real problem is that the problem is under-specified. It should call out specifically what should happen for an empty string, because as illustrated here, this is something where reasonable people may disagree. > Also giving char str[] will make it char* str. Which can be null. This may cause reading a random memory location (possibly segfault or use-after-free) Well yes, of course. The point of my comment wasn't to write bullet-proof library-ready code, it was only to illustrate two things: code like this should always go in a function, and the entire task can be accomplished in a single pass through the string. Thanks for keeping me on my toes!