Below are some frequently asked interview questions with answers:

1. Difference between BADI and user exit: BADI can have multiple implementations so several developers can work simultaneously on different implementations and different logics.For badi use SE18 and SE19 tcode and for user exit use CMOD and SMOD tcode
2. Advantage of using Field symbols : When you read from an internal table, there are no overheads for copying the table line to the work area. When you change an internal table with the MODIFY statement, you must first fill a work area with values, and then assign them to the internal table. If you work with field symbols instead, you do not have this overhead. This can improve performance if you have large or complex internal tables. It also makes it easier to process nested internal tables.You can use field symbols to make the program more dynamic. 

Also note : When we read table entries using READ or in a LOOP, we can assign them to a field symbol using the addition... ASSIGNING .it is worth using field symbols in a LOOP when the internal table has as few as 10 lines. However, it is not possible to reassign the field symbol to another field or unassign it altogether within the loop. If you include the statements ASSIGN, UNASSIGN, or the ASSIGNING addition for the same field symbol within the loop block, a runtime error occurs.