Modulus Division?

This is a discussion on Modulus Division? within the C Programming forums, part of the General Programming Boards category; Good evening! I am doing some homework. As part of the solution, I want to implement an algorithm that implements ...

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    Modulus Division?

    Good evening!

    I am doing some homework. As part of the solution, I want to implement an algorithm that implements modulus division. I was wondering if C had an operator which does just that?
    I know of the % operator, which gives you the remainder of two numbers ( 27 % 7 = 6) and that works fine 99% of the time. The only part where it fails is when I get into negative numbers. If I do - 3 % 9 in C, the answer returns -3, which makes sense as the remainder in -2. However in modulus division the answer would be 6 (modulus division considers - 3 mod 9 as -1 + (6/9), hence the answer is 6). Is there an operator that would do this sort of operation?

    I know in either VB or C# you had the "mod" reserved word which would do that nicely. A similar one exist in C?

    Thanks!

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    and the hat of wrongness Salem's Avatar
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    You could probably write your own wrapper function to detect negative parameters, and then do "the right thing".

    One more thing, % on negative numbers has implementation-specific behaviour in C.
    If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
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    ATH0 quzah's Avatar
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    Quote Originally Posted by Shamshir View Post
    If I do - 3 % 9 in C, the answer returns -3, which makes sense as the remainder in -2. However in modulus division the answer would be 6 (modulus division considers - 3 mod 9 as -1 + (6/9), hence the answer is 6).
    What? Why on earth would you expect to get -2 for the remainder?
    Quote Originally Posted by Shamshir View Post
    Is there an operator that would do this sort of operation?
    You mean an operator that would give you the completely wrong answer? Why would you want that?


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    Quote Originally Posted by quzah View Post
    What? Why on earth would you expect to get -2 for the remainder?You mean an operator that would give you the completely wrong answer? Why would you want that?


    Quzah.
    Woah relax, it was just a typo. So -3 is the remainder.

    Quote Originally Posted by Salem View Post
    You could probably write your own wrapper function to detect negative parameters, and then do "the right thing".

    One more thing, % on negative numbers has implementation-specific behaviour in C.
    Yeah, I was thinking along those lines, just was wondering if a reserved word/operator existed which would save me the trouble. But alas, here's to more lines of code!

    Thanks for your help.

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    Programming Wraith GReaper's Avatar
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    I don't agree with this "implementation-specific" approach to modulus.
    divident = divisor*quotent + remainer
    That formula implies that if divident or divisor ( or both ) are negative, the remainer will surely be negative and quotent will be negative if the divident XOR divisor are negative, otherwise it'll be positive.
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    and the hat of wrongness Salem's Avatar
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    Modulo operation - Wikipedia, the free encyclopedia
    According to this, C89/C90 is implementation-defined and C99 is defined to use the Dividend for the sign of the result.
    If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
    If at first you don't succeed, try writing your phone number on the exam paper.
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