Calculating pi with BigDecimal - problem

Hello,

I have a problem with my program that I've written:
I try to calculate pi as exact as possible with Leibniz' algorithm:

(pi/4)=(1/1)-(1/3)+(1/5)-(1/7)+(1/9).... etc.
Quickly I discovered I would need exacter numbers so I decided to use BigDecimal.
However when calculating the next term (e.g. -1/3 or 1/5) it does not calculate it correctly.

This is my code:



import java.util.Scanner;
import java.math.*;

public class Leibniz{

public static void main(String[] args)

{
Scanner in = new Scanner(System.in);
System.out.println();
System.out.println();
System.out.print("Give the number of steps to calculate pi: ");
int approx = in.nextInt();
BigDecimal approximate = new BigDecimal(0);

for (int i = 1; i<=approx; i++)
{
if(i%2==1){
BigDecimal accuracy = new BigDecimal(1/((2*i)-1));
System.out.println(accuracy);
approximate = approximate.add(accuracy);
}
else {
BigDecimal accuracy = new BigDecimal(-1/((2*i)-1));
System.out.println(accuracy);
approximate = approximate.add(accuracy);
}

}
BigDecimal final = approximate.multiply(new BigDecimal(4));
System.out.println();
System.out.print("Your approximation for pi is: ");
System.out.print(final);

}}


I put some system.out.println's to check where it goes wrong and I think it must be in the bold part....

Could anyone help me out?

Thnx in advance!

What is the reason for using BigDecimal?
What was the problem using int or long?

I dont use BigInteger but BigDecimal because calculating pi requires many ciphers after the comma.

Do you know what integer division does? e.g. 5/3 == 1 and 1/2 == 0

kind regards,

Jos

Code:

---

import java.util.Scanner; 
import java.math.*;

public class Leibniz{

    public static void main(String[] args)

    {
        Scanner in = new Scanner(System.in);
        System.out.println();
        System.out.println();
        System.out.print("geef aan hoeveel stappen je wilt zetten om pi te benaderen: ");
        int benader = in.nextInt();
        BigDecimal benadering = new BigDecimal(0);
       
        for (int i = 1; i<=benader; i++)
        {
            BigDecimal b = new BigDecimal(i);
            BigDecimal c = b.add(b);
            BigDecimal d = c.add(new BigDecimal(-1));
            BigDecimal x = new BigDecimal(1);
            BigDecimal y = new BigDecimal(-1);
            if(i%2==1){
            BigDecimal accuracy = x.divide(d);
            System.out.println(accuracy);
            benadering = benadering.add(accuracy);
            }
            else {
            BigDecimal accuracy = y.divide(d);
            System.out.println(accuracy);
            benadering = benadering.add(accuracy);
            }
           
        }
        BigDecimal eindbenadering = benadering.multiply(new BigDecimal(4));
        System.out.println();
        System.out.print("Je benadering voor pi is:");
        System.out.print(eindbenadering);
     
    }}

---

This is my new code but it gives the following error:
" at Leibniz.main(Leibniz.java:25)
java.lang.ArithmeticException: Non-terminating decimal expansion; no exact representable decimal result.
at java.math.BigDecimal.divide(BigDecimal.java:1603)
at Leibniz.main(Leibniz.java:30)
"

I replaced all the int's with BigDecimals so I could divide, multiply etc....

Thank you all for your help!
I use doubles now, a friend pointed out that computing more than 15 decimals takes too long anyway :p