Rounding function

This is a discussion on Rounding function within the C Programming forums, part of the General Programming Boards category; An assignment I'm currently doing required me to round of a float. I didn't know if there was a standard ...

  1. #1
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    Rounding function

    An assignment I'm currently doing required me to round of a float. I didn't know if there was a standard function for it or not, (if there is I couldn't find it) so I wrote my own.

    Code:
    int round(float x){
      int y = (int)x;
      if((x - y) > 0.5f){
        x = (float)++y;
      }
      else{
        x = (float)y;
      }
      return (int)x;
    }
    It works fine but I'm just seeing what people have to say about it. Maybe some tips on improvment.

  2. #2
    Registered User major_small's Avatar
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    why are you casting y to a float before assigning it to x? and why are you returning x?

    why not just increment or decrement y and return it?

    and the answer to your standard function question: kinda. ther's ceil(x) and floor(x). you can probably tell what they do from their names...

    edit:
    Code:
    int round(float x)
    {
            int y = (int)x;
            if((x - y) > 0.5f)
            {
                    ++y;
            }
            return y;
    }
    Last edited by major_small; 07-12-2005 at 07:07 PM.
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  3. #3
    Just Lurking Dave_Sinkula's Avatar
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    Test with some negative values too.
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  4. #4
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    Quote Originally Posted by major_small
    why are you casting y to a float before assigning it to x? and why are you returning x?

    why not just increment or decrement y and return it?
    heh, I don't know. I whipped it up pretty quickly. Thanks for the input.

  5. #5
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    it's work fine

  6. #6
    ATH0 quzah's Avatar
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    No it doesn't. Read Dave's post.


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  7. #7
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    Well I could test for a negative value and handle it accordingly but my program wont ever use the function with a negative value. If I intended to reuse this function then I would but in this situation it is useless to my program.

  8. #8
    aoeuhtns
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    Code:
    #include <math.h>
    Code:
    int round(float x) {
        return (int) floor(x + 0.5);
    }
    This should round -1.5 to -1, which is okay depending on what your definition of "up" is. (-1.51 rounds to -2)

    Code:
    int round(float x) {
        return (int) (x - 0.5 + (x > 0.0));
    }
    This should round -1.5 to -2, and 1.5 to 2, which is good if you have this definition of "up".

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