Java PI program issue

[Darin]

Hi all, im new here and new to java.

I have wrote this program for my hw assignment but it seems to only be accurate to the nth place after the decimal.
My instructor has given me this answer

Please enter n value: 10000
Appoximate value of pi is: 3.1415826535897198

and i get:

Please enter n value: 10000
Appoximate value of pi is: 3.1415726535897814



Here is my program. Hope this is how i am suppose to post here:

//this program finds the aprox. value of pi from a user number

import java.util.Scanner;

public class Pi
{
    public static void main (String[] args)
    {
        //create a scanner
        Scanner keyboard = new Scanner(System.in);
    
        int user; //user number
        double sum = 0;      //sum of fractions
        double fraction; //decimal value
        int i;     //loop variable
        double sign = 1;   // alt. signs  
         
   
       System.out.print("Please enter n value: ");   //ask user for integer
       user = keyboard.nextInt();   //asign userNum a value 
    
        for (i = 1; i <= user; i+=2)     //loop parameters
       {
            fraction = 1.0/i;      //gets fractions by using i as denominator
            sum = sum + sign * fraction;  //adds fractions to sum
            sign = sign * (-1);    //changes sign of fraction
       }
       
        System.out.print("Appoximate value of pi is: " + sum * 4);   //display answer
    
    }

}

Anyone have an idea on how to fix this issue?

Thanks in advance.

[Norm]

Can you post the algorithm or show the series that you are using to do the computation?

Why are you using a double to control the number of loop iterations?

Change the coloring of the post. The off yellow is unreadable.

[JosAH]

That series has a very, very slow convergence; see what happens if you add 1,000,000 terms or so. Do you get a better approximation? b.t.w. your code seems to look correct to me (I didn't give it a very close look, but note that the value of 'user' isn't the number of terms added).

kind regards,

Jos

[Darin]

Sorry JoshAH, this is the best i know how to do.

Norm,

I fixed the issues you have addressed with no avail. It still show different numbers at the end.

Can you post the algorithm or show the series that you are using to do the computation?

Im not sure what you mean by this. I have not yet learned about algorithms? But ill try to explain, I used the for loop to count all demonimators, then used the sum; fraction; and sign to perform the calculations.

pi = 4(1-1/3+1/5-1/7+1/9-1/11 ... ) and do on.

[Norm]

What value do you get if you loop 200M times

[Norm]

You must have a very slow computer to have taken so long.

[Darin]

Sorry, ill be more prompt next time.