What is the correct way to affirm a question that contains a negative?

Here’s an example:

“You don’t think x?”

If you don’t think x, does “no” mean you don’t think x, or are you negating the “don’t” and actually agreeing with x? For clarity I always respond “I don’t think x.” I’m curious though what the correct response is if you were only allowed to respond “yes” or “no.”