French language Q&A Forum

I feel like sometimes I've seen these used in an interchangeable manner (devoir and avoir à). What I told my students was that "devoir" also means "must", so "avoir à" needs to be used in situations where "must" doesn't fit (i.e. "You don't have to go yet." "Tu n'às pas encore à partir."). Is this correct? In what other situations do you need to use one over the other?