More digits in output, particular digits output, output in *.txt

This is a discussion on More digits in output, particular digits output, output in *.txt within the C++ Programming forums, part of the General Programming Boards category; I've started programming 1 week ago and I use win32 console for an output. In program which calculates pi: Code: ...

  1. #1
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    More digits in output, particular digits output, output in *.txt

    I've started programming 1 week ago and I use win32 console for an output.

    In program which calculates pi:
    Code:
    Code:
    #include <iostream>
    #include <math.h>
    using namespace std;
    
    int main()
    {
      double b=-1;
      double pi=acos(b);
      cout << pi << endl;
      
      system("PAUSE");	
      return 0;
    }
    The output is:
    Output:
    Code:
    3.14159
    I know that computer calculated pi with much higher precision, so how do I get, I don't know... 15 digits on the output screen?

    One more related question. I'm trying to write a random number generator program, since I've noticed that the rand() function doesn't have the uniform distribution of random number values, and for that I need a function that would "cut" double variable started from some decimal value to some other decimal value. For example, if I have a double variable number pi=3.141592654... I want a new integer variable with value from 3rd to 6th digit, int a=592. How do I do that?

    The final question. If I want to test relationship between many output variables it would be very usefull if program could put these values in a txt file. How do I do that? Remember (I don't know if that maters) I'm programming (or trying to ), that is, the output is in win32 console.

    Thank you!
    Last edited by Ene Dene; 11-30-2005 at 05:19 AM.

  2. #2
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    Canada
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    Do you mean PI as in PIE? Well so far it's been 100% impossible to get the exact digits for pie since the Math Professers and other researchers are still getting 3.################################### ect...

    Now I'm new as well but I might be able to just give my thought. The number PI= what your trying to get may be more bytes then a double can hold. Well thats just my guess.
    (Expert Visual Basic Programmer)
    (Newbie C/C++ Programmer)

  3. #3
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    Quote Originally Posted by dimirpaw
    Do you mean PI as in PIE? Well so far it's been 100% impossible to get the exact digits for pie since the Math Professers and other researchers are still getting 3.################################### ect...

    Now I'm new as well but I might be able to just give my thought. The number PI= what your trying to get may be more bytes then a double can hold. Well thats just my guess.
    Of course that I didn't mean PI with infinite number of digits (as I stated by "I know that computer calculated pi with much higher PRECISION, so how do I get, I don't know... 15 digits on the output screen?"), it is transcedental, by definition it is imposible, but that was not the question.

  4. #4
    ^ Read Backwards^
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    Code:
    #include <cmath>
    #include <iomanip>
    
    ....
    ....
    	cout << setprecision (15) << pi; //or any #
    .....

  5. #5
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    Thanks!

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