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I'm writing this .bat that calculates the past day.

title Past Day

set /a dayNum=%date:~0,2% - 1
set monthNum=%date:~3,2%
set yearNum=%date:~6,4%

rem Checks if it's first day of the month
if %dayNum%==0 (
    set /a monthNum-=1
    rem Checks the last day of past month
    rem For 0, 1, 3, 5, 7, 8, 10    => 31, where 0 is December[12]
    rem For 4, 6, 9, 11             => 30
    rem For 2                       => 28 or 29[leap]
    for %%a in (0, 1, 3, 5, 7, 8, 10) do (
        if %monthNum%==%%a (
            rem If, December, yearNum-1 and monthNum = 12
            if %monthNum%==0 (
                set /a monthNum=12 * 1
                set /a yearNum-= 1
            )
            set /a dayNum=31 * 1
        )
    )
    for %%a in (4, 6, 9, 11) do (
        if %monthNum%==%%a (
            set /a dayNum=30 * 1
        )
    )
    if %monthNum%==2 (
        rem Leap year check
        set /a  leap=!(%yearNum% %% 4) - !(%yearNum% %% 100) + !(%yearNum% %% 400)
        if %leap%==1 (
            set /a dayNum=29 * 1
        ) else (
            set /a dayNum=28 * 1
        )
    )
)
rem Adds leading zero 
if 0%dayNum:~1,1%==0 (
    set dayNum=0%dayNum%
)

If it's not first day, it works well, but if I force dayNum to be 0 (indicating it is first day), the output is:

>title Past Day
>set /a dayNum=0
>set monthNum=03
>set yearNum=2020
>rem Checks if it's first day of the month
- was unexpected at this moment.
>            set /a  leap=!(2020 % 4) - !(2020 % 100) + !(2020 % 400)

Using echo, the variables contents are the same as they started and, I think, the code didn't entered the if statement. The expected output is to get like dayNum=31 or dayNum=29(if leap year) and so on.

Luis Fernando
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    You are reinventing the wheel, i.e. there are lots of solutions posted on Stack Overflow how to determine date of yesterday using just pure Windows command processor commands or using (from within a batch file) other script interpreters like Windows Script Host or PowerShell to get yesterday's date. See for example my pure batch solution posted at [How to export yesterday's date keeping format \[mm/dd/yyyy\]?](https://stackoverflow.com/a/59189794/3074564) It is described very detailed. – Mofi Mar 31 '20 at 06:25
  • @Mofi thanks for the answer. I'll check your code! And about the octal, I didn't know this, thank you again. – Luis Fernando Mar 31 '20 at 13:47

0 Answers0