Mod with negatives
Hi,
Why does C return to me -9 when i calculate, -9 % 26 ?
Python gives me what i wanted -9 % 26 = 17. .....
I'm wondering if C has an implementation of mod like Python, or how to go about getting a results like Python's.
If there has been a previous discussion on this topic, plz help me to it.....
Thank you!!!
I believe the C modulus operator is undefined for negative numbers.
If you want to have a positive number, you could use integer math to solve the problem:
--Code:int mod(int x, int y) { int t = x - ((x / y) * y); if (t < 0) t += y; return t; }
Mats
Compilers can produce warnings - make the compiler programmers happy: Use them!
Please don't PM me for help - and no, I don't do help over instant messengers.
-9 / 26 = 0 with a remainder of -9. I don't know why Python gives 17 (26 + -9?) as the answer.
Why should it give you 17?
See above.
http://groups.google.com/group/comp....764926a6e6e5b6Originally Posted by Chris Torek
7. It is easier to write an incorrect program than understand a correct one.
40. There are two ways to write error-free programs; only the third one works.*
It's not undefined anymore in C99. They finally decided that the mod operator always obeys the following:
Regardless of what sign any of the quantities are.Code:a * (a / b) + (a % b) == a
Probably because Python doesn't specify the behavior either. Notice that 26 - (9 % 26) == 17, which is a typical result on many CPUs.
I thought 'modulus' is the remainder of a division? What else would it be?
7. It is easier to write an incorrect program than understand a correct one.
40. There are two ways to write error-free programs; only the third one works.*
Thanks guys for the help...
I got my program fixed already...
