value of pi

This is a discussion on value of pi within the C++ Programming forums, part of the General Programming Boards category; is there not something in C++ that has the preset value of pi? like in the math.h file? Also does ...

  1. #1
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    value of pi

    is there not something in C++ that has the preset value of pi? like in the math.h file?

    Also does anyone remeber the formula for finding the value of a shpere and the area of a circle?

  2. #2
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    Sphere V = (4/3)*R^3*PI
    Circle S = R^2*PI

  3. #3
    Confused Magos's Avatar
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    Magos

    While speaking of PI...

    How do you calculate the actual value of PI? What algoritm do you use? It would be fun to make a program that calculates it (well, not with as many decimals as the super-computers do, but still...)
    MagosX.com

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    Teach a man to fish and you feed him for a lifetime.

  4. #4
    Registered User alex's Avatar
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    The preset value of pi should be in math.h, and is called M_PI. For some reason I don't know, the microsoft version of math.h does not include this constant. You can use pi=4*atan(1).

    alex

  5. #5
    SOAK
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    #include <iostream.h>
    #include <stdio.h>
    #include <math.h>

    typedef unsigned char byte;

    int Drop();

    int iDigits,*piChain;
    byte *csDigits;

    void main()
    {
    cout<<"Number of Decimals to Calculate:\n";
    cin>>iDigits;
    cout<<"\n";
    ++iDigits;
    piChain=new int[iDigits*10/3+2];
    csDigits=new byte[iDigits+1];
    for(register int n=0;n<=iDigits*10/3+1;n++)
    piChain[n]=2;

    int lg=1;
    int m;
    for(n=0;n<iDigits;n++)
    {
    csDigits[n]=(byte)Drop();
    if(csDigits[n]==9)
    continue;
    if(csDigits[n]==10)
    {
    for(m=lg;m<n;m++)
    {
    if(csDigits[m]!=9)
    {
    csDigits[m]=1+csDigits[m];
    }
    else
    {
    csDigits[m]=0;
    }
    }
    csDigits[n]=0;
    lg=n-1;
    continue;
    }
    lg=n;
    }
    cout<<(int)csDigits[0]<<",\n";
    for(n=1;n<iDigits;n++)
    {
    cout<<(int)csDigits[n];
    }
    cout<<"\n";
    delete[] piChain;
    delete[] csDigits;
    }

    int Drop()
    {
    int r,q,iDrop;
    for(int m=0;m<=iDigits*10/3+1;m++)
    piChain[m]=piChain[m]*10;
    for(m=(iDigits*10/3+1);m>1;m--)
    {
    q=(int)floor(piChain[m]/(2*m-1));
    r=piChain[m]%(2*m-1);
    piChain[m]=r;
    piChain[m-1]+=(q*(m-1));
    }
    iDrop=(int)floor(piChain[m]/10);
    piChain[m]=piChain[m]%10;

    return iDrop;
    }

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