Bat script - subtracting a month, what am I doing wrong?

Question

cmd/bat

set dd=%DATE:~0,2%
set mm=%DATE:~3,2%
set yyyy=%DATE:~6,4%
echo %mm%
IF %mm:~0,1% EQU 0(SET mm=%mm:~1,1% )
set /a mm=%mm%-1
 echo %mm%
pause

Conclusion
As you can see in the output - set puts the value 9 instead of 09, but then 09 comes again in the mm variable, what should I change to solve the problem?

Answer 1

The code is working, the problem was in the script file itself.