@echo off
echo 设: a+b=c
echo 输入a b c 任意两个值，求得另一个未知数 ?=
for %%i in (a b c) do set %%i=?&set/p %%i=%%i=?

if %a%==? set/a a=c-b&call echo a=%%a%%
if %b%==? set/a b=c-a&call echo b=%%b%%
if %c%==? set/a c=a+b&call echo c=%%c%%

pause
::极简单的题要用这么多 if 吗？有人说用goto但也要分三种情况解决吧！
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@echo off&setlocal enabledelayedexpansion
set var=?+3=8
for /f "tokens=1-3 delims=+=" %%a in ("%var%") do (
   if "%%c"=="?" (set ss=%%a+%%b) else (
      set %%a=%%b&set %%b=%%a&set "ss=%%c-!?!"
    )
)
set /a num=%ss%
echo !var:?=%num%!
pause
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@echo off
:start
setlocal enabledelayedexpansion
echo;&echo 请输入算式如：5*?=40
set /p var=&cls
set "var2=%var:?=%"
set .-=a&set ./=a&set +=-&set -=+&set /=*&set "*=/"
for /l %%a in (0 1 9) do set var2=!var2:%%a=!
set "ff=%var2:~0,1%"&set "f=!%var2:~0,1%!"
for /f "tokens=1-3 delims=+-/*=" %%a in ("%var%") do (
   if "%%c"=="?" (set ss=%%a%ff%%%b) else (
      if "%%a"=="?" (set ss=%%c%f%%%b) else (
         if defined .!ff! (set ss=%%a%ff%%%c) else set "ss=%%c%f%%%a"
)))
set /a num=!ss!
set "str=!var:?=%num%!"
echo 你输入的是：%var%
echo 计算结果是：!str!
endlocal&goto start
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