How do you know if a confident boy likes you?

If he smiles at you consistently, goes out of his way to talk to you, asks for your number, asks to spend time with you with his friends or by yourselves. Those are all sure-fire signs that he may be interested. If he's done all of the above, I'd be confident enough to ask him, and that'll show him that you can match his confidence with your own, and it may spark more interest. :-)