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!

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.

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.

Code:

#include <cmath>
#include <iomanip>

....
....
	cout << setprecision (15) << pi; //or any #
.....

Thanks!