"You have a cat."
Translation:Vous avez un chat.
Many times in French questions are formed by making a statement and raising the inflection of the voice at the end. So vous avez un chat means "you have a cat" but also means "do you have a cat" when the inflection is raised at the end.
Saying "avez-vous" is called inversion and is another way to ask a question in French though I hear less popular.