复制这个代码，执行一下，可以解决你的问题，在我这里测试是通过的。
@echo off&setlocal EnableDelayedExpansion
set num1=0
set num2=0
for /f "delims= " %%i in (a.txt) do (
set var=%%i
if defined var goto begin
)
:begin
for /f "skip=1 delims= " %%i in (a.txt) do (
set bar=!var!
set var=%%i
set /a car=!var!-!bar!
echo !car!>>b.txt
)
set /a car=!bar!-!bar!
echo !car!>>b.txt
goto insert
:insert
for /f "tokens=1,2 delims= " %%a in (a.txt) do (
set /a num1+=1
for /f "delims=" %%i in (b.txt) do (
set /a num2+=1
if !num1!==!num2! echo %%a %%i %%b>>c.txt
)
set num2=0
)
del b.txt
endlocal
goto :eof
