i want vba code to insert serial number based on cell value

[Prasad K]

i want vba code to insert serial number based on cell value like this below

Column A | Serial No Column B | Data if i enter data in column B then insert serial number in column A Automatically & if i delete any data row then the serial number should be update has serial

 

[Joe4]

Is your Serial Number really just a row counter, like you have shown, or have you "simplified" the data for the sake of posting it here?
If you have simplified it, can you post a more realistic data sample, so we can see what kind of "pattern" you are using to determine the next value?

Note that if it really is just a row counter, you could use a formula like this (put in cell A2), and copy down column A further than you would ever need and it would show what you want (no VBA required):

=IF(B2<>"",ROW()-1,"")