::原理：展转相除法
::code by youxi01@bbs.bathome.net 2007-10-24
@echo off & setlocal enabledelayedexpansion
if "%1"=="" goto :help
call :loop %1 %2
echo.
echo %1和%2之间的最大公约数为：!deno! 最小公倍数为：!multi!
pause>nul
:loop %1 %2
set /a var=%1 %% %2,deno=%2
if !var! neq 0 call :loop %2 !var!
set /a multi=%1*%2/!deno!
goto :eof
:help
echo.&echo ==========================求最大公约数和最小公倍数=================
echo [使用格式]    %~0 %1 %2
echo [使用示例]    %~0 12 42
echo ============================--------=================================
cmd /k
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@echo off&setlocal enabledelayedexpansion
:begin
echo====================
set /p num1=第一个数:
set /p num2=第二个数:
call :gcd %num1% %num2%
:gcd
set a=%1
set b=%2
:start
set /a num=a%%b
if %num% gtr 0 (
     set /a b=!a!%%!b!
     set /a a=%b%
     goto start
)else (
     echo 最大公约数:!b!
     set /a sum=%1*%2/!b!
     echo 最小公倍数:!sum!
     goto begin
)
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echo off&cls
set /p num1=输入第一个数：
set /p num2=输入第二个数：
if %num1% LSS %num2% ^
set num1=%num2% & set num2=%num1%
:LOOP
set TMP=
set /a tmp=%num1%%%num2%
if %tmp% neq 0 (
	set /a num1=num2
	set /a num2=tmp
) else (
	call :end %num2%
	exit
)
goto loop

:end
echo 它们的最大公约数是%1。
pause
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@echo off

set /a a=%random%,b=%random%

rem swap a & b to makes a >= b if nessary
set /a "c=((a-b)>>31)+1"
set /a "d=c*a+(1-c)*b"
set /a "e=(1-c)*a+c*b"
rem echo %a% %b% %c% %d% %e%
set /a "a=d,b=e"

rem get greatest common divisor of a & b into a
:g0
set /a "c=a%%b,a=b,b=c,gend=!c"
rem echo %a% %b%
goto g%gend%

:g1
echo %d% %e% -^> %a%
pause
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