set /a sd-=input
if %sd% leq 0 call :count
cls
echo.&echo.
echo 指定的日期是：%day%
echo.
set sm=0%sm%
set sd=0%sd%
echo %input% 天前的日期是：%sy%-%sm:~-2%-%sd:~-2%
pause>nul
goto Main
:count
set /a sm-=1
if !sm! equ 0 set /a sm=12, sy-=1
call :days
set /a sd+=days
if %sd% leq 0 goto count
goto :eof
:days
:: 获取指定月份的总天数
set /a leap="^!(sy %% 4) & ^!(^!(sy %% 100)) | ^!(sy %% 400)"
set /a max=28+leap
set num=0
set str=31 %max% 31 30 31 30 31 31 30 31 30 31
for %%i in (%str%) do (
set /a num+=1
if %sm% equ !num! set days=%%i&goto :eof
)
goto :eof
