Yeah, I'd probably google that in any language I've written, including ones I've worked in in the last couple weeks. Even if I thought I knew what to do, and even if I tried it and it seemed to do the right thing, I'd google it (or use in-IDE docs, or similar) because I wouldn't trust that I was entirely correct.
... however, narrow the question and give me some resources ("the input will be a positive, unsigned 32-bit integer; the string should be ascii and use digits, not words, to represent the number; do insert commas every third digit [and we're working exclusively in English, so commas are all we need and you can ignore system locale preferences—one of many subtle ways one might screw this up]; here's a printout of an ascii table for reference") and I can probably do something like what's requested, without the aid of Google. As long as you don't expect the syntax to be completely perfect.