"Sure do!" (3)
'sure do' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for yep that I've seen before include "Affirmative (US colloq.)" , "informal approval" , "Positive reaction" , "Correct" .)
(Other definitions for yes that I've seen before include "Affirmative answer" , "Yea" , "Affirmative reply" , "Aye" , "Absolutely" .)