Question

why we use AC and BC after every year like 663BC give me the reason which is correct

Answer 1

Both are different things..
AC means After Christ
whereas
BC means Before Christ.
The terms after Christ(AC) and before Christ (BC) are used to label or number years in the Julian and Gregorian calendars.
This calendar era is based on the traditionally reckoned year of the conception or birth of Jesus of Nazareth, with AC counting years from the start of this epoch, and BC denoting years before the start of the era.