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C++ pi

  1. Jul 1, 2004 #1
    How would I go about defining pi (and using) as 3.1415926535897932384626433832795?

    I've tried using double, long double and #define pi 3.1415926535897932384626433832795 but it, instead, takes 3.14159.
    Is there any way to get it more accurate?
     
  2. jcsd
  3. Jul 1, 2004 #2

    Hurkyl

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    I believe the default precision for printf and cout is to only display 6 digits; try changing the precision in your display routines.

    (Oh, and I see M_PI in my math.h include file; that might be standard)
     
  4. Jul 1, 2004 #3

    dduardo

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    If you want to hold such a precise number your going to have to write your own function. A long double will hold about 18 digits with an error of +- 2e-15 depending on the system your using. cout will be less precise with a define macro.
     
  5. Jul 1, 2004 #4
    Many thanks. I didn't even know the precision thing exist(fairly new to all this) but a quick google search sorted all that out. Thanks again Hurkyl.

    edit:dduardo, I figured I don't really need it to be so accurate, so I settled with just 15 digits. Thanks for your reply.
     
    Last edited: Jul 1, 2004
  6. Jul 1, 2004 #5

    robphy

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    4.0*atan(1.0)
     
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