Do I need apple care in order to trade in cracked iPhone at apple store?

Do I need to have the apple care in order to trade in my IPhone 4S that is severely damaged for a new one?

You still need to have the one year warranty. If you have had it for more than a year, you need Apple Care

No. But without AP+ they will charge you $199 for a replacement. The 1 year warranty is a manufacturers warranty. Having AP+ lowers it to $79 so it pays for itself within one incident.

They can't sell AP+ to a damaged phone and regular Applecare doesn't cover damage. You can only puchase Applecare+ within the first 30 days of purchase. You can't put it on a replacement phone since it works off the existing warranty.