Access IIF to SQL statement convert

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VB

("select IIF(MAX(bill_bno) IS NULL,1,MAX(bill_bno)+1) from rec_all where rw=0 and iif(month(bill_date)>=1 AND month(bill_date)= 1 And Month(Date) <= 3, Year(Date) - 1, Year(Date)))

What I have tried:

I have access query and I am converting it to SQL Server 2012. I'm looking for the equivalent to the Access IIF statement in SQL Server.

Below is the statement I am trying to convert;