fact.bat

@echo off

rem http://e-arrows.sakura.ne.jp/2010/08/is-lisp-really-has-too-many-parenthesis.html
rem 引数が13くらいからおかしくなるので注意

setlocal

set ret=1
set num=%1%
:while
if %num% equ 0 goto endwhile
SET /a ret=%ret% * %num%
SET /a num=%num% - 1
goto while
:endwhile
echo %ret%

endlocal