Why does modulus division only work with integers

Question

I recently ran into an issue that could easily be solved using modulus division  but the input was a float      Given a periodic function  e g  sin  and a computer function that can only compute it within the period range  e g   -p  p    make a function that can handle any input    The  obvious  solution is something like    include  lt cmath gt   float sin float x       return limited sin  x   M PI     2  M PI  - M PI       Why doesn t this work  I get this error    error  invalid operands of types double and double to binary operator     Interestingly  it does work in Python    def sin x       return limited sin  x   math pi     2   math pi  - math pi

User · Accepted Answer

Because the normal mathematical notion of "remainder" is only applicable to integer division. i.e. division that is required to generate integer quotient.

In order to extend the concept of "remainder" to real numbers you have to introduce a new kind of "hybrid" operation that would generate integer quotient for real operands. Core C language does not support such operation, but it is provided as a standard library fmod function, as well as remainder function in C99. (Note that these functions are not the same and have some peculiarities. In particular, they do not follow the rounding rules of integer division.)

User · Answer

try fmod

User · Answer

I can t really say for sure  but I d guess it s mostly historical  Quite a few early C compilers didn t support floating point at all  It was added on later  and even then not as completely -- mostly the data type was added  and the most primitive operations supported in the language  but everything else left to the standard library

User · Answer

The mathematical notion of modulo arithmetic works for floating point values as well  and this is one of the first issues that Donald Knuth discusses in his classic The Art of Computer Programming  volume I   I e  it was once basic knowledge    The floating point modulus operator is defined as follows   m   num - iquot den   where iquot   int  num den     As indicated  the no-op of the   operator on floating point numbers appears to be standards related  The CRTL provides  fmod   and usually  remainder  as well  to perform   on fp numbers  The difference between these two lies in how they handle the intermediate  iquot  rounding    remainder  uses round-to-nearest  and  fmod  uses simple truncate   If you write your own C   numerical classes  nothing prevents you from amending the no-op legacy  by including an overloaded operator     Best Regards

User · Answer

The modulo operator   in C and C   is defined for two integers  however  there is an fmod   function available for usage with doubles

User · Answer

The   operator does not work in C    when you are trying to find the remainder of two numbers which are both of the type Float or Double   Hence you could try using the fmod function from math h   cmath h or you could use these lines of code to avoid using that header file   float sin float x     float temp   temp    x   M PI      2  M PI  - M PI    return limited sin  x   M PI  -   2  M PI  - M PI    temp

User · Answer

The   operator gives you a REMAINDER another name for modulus  of a number   For C C    this is only defined for integer operations   Python is a little broader and allows you to get the remainder of a floating point number for the remainder of how many times number can be divided into it    gt  gt  gt  4   math pi 0 85840734641020688  gt  gt  gt  4 - math pi 0 85840734641020688  gt  gt  gt

User · Answer

The constraints are in the standards   C11 ISO IEC 9899 201x    6 5 5 Multiplicative operators     Each of the operands shall have arithmetic type  The operands of the   operator shall   have integer type    C  11 ISO IEC 14882 2011    5 6 Multiplicative operators     The operands of   and   shall have arithmetic or enumeration type  the operands of   shall have integral or enumeration   type  The usual arithmetic conversions are performed on the operands and determine the type of the result    The solution is to use fmod  which is exactly why the operands of   are limited to integer type in the first place  according to C99 Rationale   6 5 5 Multiplicative operators      The C89 Committee rejected extending the   operator to work on floating types as such usage would duplicate the facility provided by fmod

User · Answer

You re looking for fmod     I guess to more specifically answer your question  in older languages the   operator was just defined as integer modular division and in newer languages they decided to expand the definition of the operator   EDIT   If I were to wager a guess why  I would say it s because the idea of modular arithmetic originates in number theory and deals specifically with integers

[c++] Why does modulus division (%) only work with integers?

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