Calculating Pi Java Program

Question

I'm taking my first Java programming class and this is my first class project. I'm so confused about how to approach it. Any help or correction will be appreciated.

You can approximate the value of the constant PI by using the following series:

PI = 4 ( 1 - 1/3 + 1/5 - 1/7 + 1/9 - 1/11 + ... + ( (-1)^(i+1) )/ (2i - 1) )

Prompt the user for the value of i (in other words, how many terms in this series to use) to calculate PI. For example, if the user enters 10000, sum the first 10,000 elements of the series and then display the result.

In addition to displaying the final result (your final approximation of PI), I want you to display along the way your intermediate calculates at every power of 10. So 10, 100, 1000, 10000 and so on, display to the screen the approximation of PI at that number of summed elements.

This is what i did so far ..

import java.util.Scanner;
        public class CalculatePI {

            public static void main(String[] args) {
                // Create a Scanner object
                Scanner input = new Scanner (System.in);

                // Prompt the user to enter input
                System.out.println("Enter number of terms");
                double i = input.nextDouble(); // value of i user entered
                    double sum = 0;
                for(i=0; i<10000; i++){
                           if(i%2 == 0) // if the remainder of `i/2` is 0
                           sum += -1 / ( 2 * i - 1);
                        else
                           sum += 1 / (2 * i - 1);
    }

                        System.out.println(sum);


    }
}

Answer 1

First thing I see is you attempting to return a value from your void main method.

don't return pi; from your main method. Print it.

System.out.println(pi);

---

Secondly, when people write a for loop, they're commonly iterating over i, which is probably the same i that your professor referred to in the formula

for(double i=0; i<SomeNumber; i++)
{
    sum += ((-1)^(i+1)) / (2 * i - 1) );
}

now, that won't work correctly as is, you still have to handle the ^, which java doesn't use natively. luckily for you, -1^(i+1) is an alternating number, so you can just use an if statement

for(double i=0; i<SomeNumber; i++)
{
    if(i%2 == 0) // if the remainder of `i/2` is 0
        sum += -1 / ( 2 * i - 1);
    else
        sum += 1 / (2 * i - 1);
}

Answer 2

sometimes the answer is a simple line of code. Also you are reassigning i to 0 so Im assuming you are using the user input in the wrong way.

for(int counter=1;counter<input;counter++){
    sum += Math.pow(-1,counter + 1)/((2*counter) - 1);
}

for input that should can be any variable, hard coded or set by user input (such as 1000, 10000, 100000). This should work