CMD set /a, modulus, and negative numbers
Solution 1
The %
in CMD much like in other microsoft environments is a remainder function - not a true modulo operation. The remainder is accurate here to return -6 for your examples. Using mod
in Excel is a true modulo which does return your expected 1.
Although it's written for C#, the article below has a great breakdown of the difference: http://blogs.msdn.com/b/ericlippert/archive/2011/12/05/what-s-the-difference-remainder-vs-modulus.aspx
Solution 2
If you want true modulo, than you can use this:
set a=-90
set b=7
set /a (a%b+b)%b
Solution 3
As Jason W said, %
isn't a modulo operator. But if you want -b mod N, maybe this can help:
@echo off
set /a num1=7
set /a num2=-90
:add
if %num2% LSS 0 set /a num2+=num1&goto add
echo/%num2%
pause
unclemeat
IT apprentice; currently working in networking, previously working in virtualization.
Updated on June 25, 2022Comments
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unclemeat over 1 year
Is CMD unable to evaluate the modulus of negative numbers using
set /a
?90 % 7
correctly equates to 6 in batch, however-90 % 7
gives -6 instead of 1.I thought that it might have been evaluating
-(90 % 7)
, but this doesn't seem to be the case as(-90) % 7
also gives -6.h:\uprof>set /a -90%7 -6 h:\uprof>set /a (-90)%7 -6
So - is this a limitation of CMDs set /a Modulus operator?
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unclemeat almost 9 yearsThanks, I have found another expression which does not require calculating the modulus of negative numbers - at the expense of a few bytes (for CodeGolf).