DIDN'T USE TO - NEGATIVES

We use "Didn't use to" + Verb in base form to express that an action wasn't part of a routine.

For example:

I didn't use to wake up early when I was a kid.

Sam didn't use to ride a bike to work.

DID .... USE TO...? - QUESTIONS

We use DID + subject + USE TO + VERB in Base Form to ask if an action is a past habit.

For example:

Did you use to play video games as a kid?

Did Chris use to take the bus to school?