A user has posted a question on Stack Overflow (but it could have been any Stack Exchange site) and I have added some comments. The user has got the answer through my comments. What next – the question is still open?
If you have answered their question, compile your comments into a full-fledged answer (and delete the comments to reduce the noise). Comments are meant to improve the question; if you accidentally happen to answer the question, no problem at all, but turn those temporary notes into a permanent post. Remember that we're not only here to help the author of the question, but also future visitors with the same problem.