flaot -double comparison

This is a discussion on flaot -double comparison within the C Programming forums, part of the General Programming Boards category; I m getting equal as output... My doubt is float compared with double in if statement, then it should b ...

  1. #1
    C is Sea. I know a drop! ganesh bala's Avatar
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    Question flaot -double comparison

    I m getting equal as output...

    My doubt is float compared with double in if statement,
    then it should b unequal right??

    Is it something like type conversion?? I want just to clarify this point..




    Code:
    int main()
    {
        float a=7.0; //6.9999999
        a=a+0.0000001;// 7.0f
        if(a==7.0)
             printf("equal");
        else
             printf("unequal");
             
             getchar();
             
             }

  2. #2
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    Floating point values (with rare exceptions) can not be compared for equality with constants (or values derived from constants other than those making up the original number). In general, comparing floating point for "is this equal to that" should really be done as "delta" comparisons, e.g.
    Code:
    if (fabs(a-b) < 0.000001) 
       printf("equal");
    else
       printf("not equal");

    --
    Mats
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  4. #4
    Technical Lead QuantumPete's Avatar
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    Quote Originally Posted by matsp View Post
    should really be done as "delta" comparisons,
    I think the constant you compare to is called epsilon.

    QuantumPete
    Last edited by QuantumPete; 02-24-2009 at 03:37 PM.
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    Algorithm Dissector iMalc's Avatar
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    A float cannot distinguish 7.0000001 from 7 because it does not have enough significant bits to do so. The range of magnitudes of those numbers is too great.
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