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I started learning java yesterday. Since I know other programming languages, it's easier for me to learn Java. It's pretty cool, actually. I still prefer Python :) Anyhoo, I wrote this program to calculate pi based on the algorithm (pi = 4/1 - 4/3 + 4/5 - 4/7....) and I know there are more efficient ways of calculating pi. How would I go about doing this?

import java.util.Scanner;

public class PiCalculator
{
  public static void main(String[] args)
  {
    int calc;
    Scanner in = new Scanner(System.in);
    System.out.println("Welcome to Ori's Pi Calculator Program!");
    System.out.println("Enter the number of calculations you would like to perform:");
    calc = in.nextInt();
    while (calc <= 0){
      System.out.println("Your number cannot be 0 or below. Try another number.");
      calc = in.nextInt();
    }
    float a = 1;
    float pi = 0;
    while (calc >= 0) {
      pi = pi + (4/a);
      a = a + 2;
      calc = calc - 1;
      pi = pi - (4/a);
      a = a + 2;
      calc = calc - 1;
    }
    System.out.println("Awesome! Pi is " + pi);
  }
}

The result of this code, after 1,000,000 calculations is still 3.1415954. There HAS to be a more efficient way of doing this.

Thanks!

JAL
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Ori Yonay
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    possible duplicate of [How to determine whether my calculation of pi is accurate?](http://stackoverflow.com/questions/14283270/how-to-determine-whether-my-calculation-of-pi-is-accurate) – sinclair Aug 20 '15 at 14:58
  • have you tried the Nilakantha series? – jhamon Aug 20 '15 at 14:59
  • [yes](https://cs.uwaterloo.ca/~alopez-o/math-faq/mathtext/node12.html)... yes there is. – Tawcharowsky Aug 20 '15 at 15:01
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    @BrianAgnew this question is a poor fit for Programmers - it would be quickly voted down and closed over there, see http://meta.programmers.stackexchange.com/questions/6483/why-was-my-question-closed-or-down-voted/6490#6490 Recommended reading: **[What goes on Programmers.SE? A guide for Stack Overflow](http://meta.programmers.stackexchange.com/q/7182/31260)** – gnat Aug 20 '15 at 15:24
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    I am missing the Java component in this question. Yes its written in Java, but its entirely about calculating PI. You can translate this code to Python and the question would remain unchanged. – Gimby Aug 20 '15 at 15:30
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    You use `float` for each term, thus accumulating rounding errors. This won't give you accurate result. – Alex Salauyou Aug 20 '15 at 15:33

2 Answers2

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The most efficient way to calculate Pi in Java is to not calculate it at all:

System.out.println("Awesome! Pi is " + Math.PI);

Though your question isn't clear about this, my guess is that you are actually trying an exercise. In this case, you could try the Nilakantha series:

float pi = 3;
for(int i = 0; i < 1000000; i += 2) {
    pi += 4 / (float) (i * (i + 1) * (i + 2));
}

Even more efficient and accurate is Machin's formula:

float pi = 4f * (4f * Math.atan(5) - Math.atan(239)) / 5f;
L3R5
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Why not use Python’s generator expression to implement Leibniz formula for π (one liner :)) :

4*sum(pow(-1, k)/(2*k + 1) for k in range (10000))
Giri
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