Probably, I'm guessing at the problem but I assume "it doesn't work".
Try this
@echo off
echo Testing Set /P and Set /A
set /p NUM1=Enter a number :
set /p NUM2=Enter another number :
set /a RESULT=NUM1+NUM2
echo %NUM1% + %NUM2% = %RESULT%
REM your stuff corrected
set var=5
echo %var%
set /a var=var+1
echo %var%
pause