Question

I have written a rather small batch file that does some date calculations for me.

However, I have stumbled upon a minor problem:

Whenever I try to increment my month var, it simply sets the var to the desired incrementation. Code:

: How much time should we add? Default is 1 month
SET timeadd=1

: Set the date variables to build needed format
SET YYYY=%date:~-4%
SET MM=%date:~3,2%
SET DD=%date:~0,2%

if not %MM%==12 (
    SET /A MM=MM+timeadd
    SET changed=1
)

After the declaration, the month var would today (August 17th) be “08”.

After the if block however, this var would change to “1”.

I could guess that this is a conversion problem (date beeing a string, timeadd beeing an integer), however I really have no clue how to solve this.

Answer 1

As said in the comments, this is happening because a leading 0 indicates octal notation (just like a leading 0x indicates Hex notation), but the octal numbering system runs from 01 to 07, so there is no octal 08 or 09, rather it would be 010 and 011.

Decimal Value 8 == Octal Value 010

Decimal Value 9 == Octal Value 011

To verify this for yourself, type this at the command-prompt

c:\>set /a 010
c:\>set /a 011

Your output will be:

8
9

=======================================

My solution to this is simply to check for any leading 0‘s and delete them.

if "%MM:~0,1%"=="0" set MM=%MM:~-1%

Do any mathmatical magic I need done…

set /a MM=%MM% + 1

…and then add the leading 0‘s back on if necessary.

set MM=0%MM%
set MM=%MM:~-2%

Just remember to make sure that it doesn’t exceed 12 (in this instance) or get lower than 1.