Holy cow, I wrote a book!
The command processor CMD.EXE comes with a mini-calculator
that can perform simple arithmetic on 32-bit signed integers:
C:\>set /a 2+2
C:\>set /a 2*(9/2)
C:\>set /a (2*9)/2
C:\>set /a "31>>2"
Note that we had to quote the shift operator since it would
otherwise be misinterpreted as a "redirect stdout and append" operator.
For more information, type
set /? at the command prompt.