How does modulus operation works with float data type?

Question

I m trying to find out a simple modulus operation on float data type.

float a=3.14f;
float b=10f;
result=a%b;

I m getting result= 3.14

Another example using decimal data types:

decimal p=10;
decimal q=40;
result=p%q;

getting answer=20.

I am not understanding how does modulus works?

Answer 1

From the C# language spec on floating point remainder. In the case of x % y if x and y are positive finite values.

z is the result of x % y and is computed as x – n * y, where n is the largest possible integer that is less than or equal to x / y.

The C# language spec also clearly outlines the table of what to do with the cases of all possible combinations of nonzero finite values, zeros, infinities, and NaN’s which can occur with floating point values of x % y.

                          y value

                | +y  –y  +0  –0  +∞  –∞  NaN
           -----+----------------------------  
  x         +x  | +z  +z  NaN NaN x   x   NaN
            –x  | –z  –z  NaN NaN –x  –x  NaN
  v         +0  | +0  +0  NaN NaN +0  +0  NaN
  a         –0  | –0  –0  NaN NaN –0  –0  NaN
  l         +∞  | NaN NaN NaN NaN NaN NaN NaN
  u         –∞  | NaN NaN NaN NaN NaN NaN NaN
  e         NaN | NaN NaN NaN NaN NaN NaN NaN

Answer 2

This article on msdn has sufficient example but I can explain it real quick;

http://msdn.microsoft.com/en-us/library/0w4e0fzs.aspx

If you do int result = x % y; what you'll find is that you are returned the remainder of x % y and the values are treated more like whole numbers. For example, the third line in the link is Console.WriteLine(5.0 % 2.2); which prints .6. This is because it finds that 2.2 can go into 5.0 no more than twice. So it does 5 - 2.2(2) which is .6