@ECHO OFF
 
SETLOCAL
 
SET X=10
 
CALL :Fib %X% Y
ECHO Fib^(%X%^)=%Y%
GOTO :EOF
 
:Fib [In]X [Out]Result
SETLOCAL
SET A=%1
SET D=1
SET E=0
 
IF %A% LEQ 1 (
  GOTO FibRet
)
 
SET /A B=%A%-1
SET /A C=%A%-2
CALL :Fib %B% D
CALL :Fib %C% E
 
:FibRet
ENDLOCAL & SET /A %2=%D%+%E% & GOTO :EOF