Hi!,

I'm trying to write a short code for my own curiosity that will "sieve out" prime numbers from a range of positive integers (with an upper bound defined by the user) by dividing each integer within the set by all the previous integers before it (i.e. 5 by 1, 2, 3, and 4) and evaluating the remainders for 0 values (except when dividing by 1 and the number itself), and then adding the prime numbers to an array list which will display itself at the end.

For example:

User inputs the value 10 as an upper bound.

We assume 1 is a prime number and add it to our array list to start.

The program will then divide 2 by 1 and 2, then 3 by 1, 2 and 3, then 4 by 1, 2, 3 and 4; and so on and so forth.

If the remainder of any of these operations (except in the case of division by 1 and the number we are currently evaluating) is equal to zero, the program moves on to the next number in the list until it has evaluated every integer up to/including 10.

If none of the operations result in a remainder equal to 0 (except, again, in those special cases noted above), the number will be added to the array list before moving on to the next number in the sequence.

The array list will display [1, 2, 3, 5, 7] at the end.

So far the code I have written is as follows (it was a relatively short code, so I'm including the entire thing here so you can follow the operations if you'd like):

Code Java:

import java.util.Scanner; import java.util.*; public class EratosthenesSieve { public static void main(String args[]) { Scanner keyboard = new Scanner(System.in); ArrayList list = new ArrayList(); list.add(1); int boundary = 0; System.out.println("Please enter the positive integer you would like evaluated to:"); boundary = keyboard.nextInt(); while (boundary < 1) { System.out.println("I'm sorry, but that's not a valid number. Please enter a positive integer " + "to be evaluated to:"); boundary = keyboard.nextInt(); } int counter = 2; int currentNumber = 2; int remainder = 0; do { while(counter <= currentNumber) { remainder = currentNumber % counter; System.out.println("Your remainder for this operation is: " + remainder); if (remainder == 0 && counter != currentNumber) { currentNumber++; counter = 2; } else if (remainder == 0 && counter == currentNumber) { list.add(currentNumber); currentNumber++; counter = 2; } else if (remainder > 0) { counter++; } } } while (currentNumber < boundary); System.out.println("Your prime numbers are: " + list); } }

Currently when it runs, it gets stuck in an infinite loop inside of the first do-while, and I'm not sure why... I'm hoping it's something blindingly obvious that I'm just not seeing (I haven't programmed in well over a year, so I'm rusty at best) but I'm not too sure about the logic of those loops, either. Anyway, I've been staring at this for hours now and I can't figure out what's going on, so I would very much appreciate any advice/insight about this that anyone has to offer! :) (Thanks either way!)

~dp