Used to + Infinitive

Affirmative	Negative		Interrogative
	Long Form	Contracted Form
I used to smoke	I did not use to smoke	I didn't use to smoke	Did you use to smoke?

The structure used to + infinitive is used to refer to a past habit or situation
which no longer exists at the present time.

• It refers to past habits and states that do not exist today, something that
  you did regularly or repeatedly in the past but no longer do today.
• It exists only in the past.
  
  Here are some examples :
  
  
  • Tom used to drink coffee.  Now he prefers tea.
  • Julie used to fly from London to Paris.  Now she takes the Eurostar.
  • I used to drive to work.  Now I take the underground.
  • Bill used to live in Wales.  Now he lives in Scotland.
  • Wendy used to eat meat.  Now she's a vegetarian.
• This structure cannot be used to say how often something happened,
      or how long it took.
  • Julie used to visit Paris seven times. Julie visited Paris seven times.
  • Bill used to live in Wales for three years. Bill lived in Wales for three years.