Math Issues

This is a discussion on Math Issues within the C Programming forums, part of the General Programming Boards category; Umm... Hi. Whenever... 33.3 + 33.3 + 33.3 = 99.89999 or 33.3 * 3 = 99.8999 Why doesn't it equal ...

  1. #1
    Registered User Berserker's Avatar
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    Math Issues

    Umm... Hi.

    Whenever...

    33.3 + 33.3 + 33.3 = 99.89999

    or

    33.3 * 3 = 99.8999

    Why doesn't it equal 99.9?



    -Berserker

  2. #2
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    umm..

    whenever question bad....

    answer = ?

    and

    cannot help

    Why not post code?
    i seem to have GCC 3.3.4
    But how do i start it?
    I dont have a menu for it or anything.

  3. #3
    & the hat of GPL slaying Thantos's Avatar
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    Because floating point numbers can not respresent every number accurately. However 99.9 does = 99.89999999999999999999999999999999999999999999999 9999999999(to infinity)

  4. #4
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    Sorry Calculating a triangle's perimeter.

    void perimeter(void)
    {

    float perimeter, a, b, c;

    printf("Please input side A > ");
    scanf("%f", &a);
    printf("Please input side B > ");
    scanf("%f", &b);
    printf("Please input side C > ");
    scanf("%f", &c);
    perimeter = a + b + c;
    printf("\nThe final solution is... > %.5f\n\n", perimeter);
    }

  5. #5
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    Quote Originally Posted by Thantos
    Because floating point numbers can not respresent every number accurately. However 99.9 does = 99.89999999999999999999999999999999999999999999999 9999999999(to infinity)
    Is there any way I can accurately depcit all numbers?

  6. #6
    & the hat of GPL slaying Thantos's Avatar
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    Nope. Due to memory limitations and per fact that some numbers just never end it's impossible to accurately store all numbers. What you have to do is decide how close is close enough.

    Edit: you can also try using double instead of float but I don't know how much difference it'll make in this case.

  7. #7
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    Quote Originally Posted by Thantos
    Nope. Due to memory limitations and per fact that some numbers just never end it's impossible to accurately store all numbers. What you have to do is decide how close is close enough.

    Edit: you can also try using double instead of float but I don't know how much difference it'll make in this case.
    Perhaps that is what I don't understand.
    To me, 3.33 + 3.33 + 3.33 should equal 99.9. Not 99.8999...
    I know it can't store all numbers, but it should accurately depict the numbers displayed.
    It screws up Pi too, but that is more understandable.
    Oh well, I guess I'll never understand it.
    Thanks anyway.

    PS: Double did the same as float.

  8. #8
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    Here is an explanation of fixed-point math, which may also help explain what flaoting point numbers are doing to confuse you.

    http://www.wwnet.net/~stevelim/fixed.html

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    You could also have a look at arbitrary-precision math libraries, like http://www.tc.umn.edu/~ringx004/mapm-main.html

  10. #10
    Registered User Codeplug's Avatar
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