Java Display the Prime Factorization of a number

RikYC picture RikYC · Sep 24, 2012 · Viewed 43.2k times · Source

So for my assignment, I have to write a program that asks the user for an integer input and then print out that number's prime factorization. This is what I have:

import java.util.Scanner;

public class PrimeFactor {
    public static void main(String[] args) {
        System.out.print("Enter a positive number: ");
        Scanner scanner = new Scanner (System.in);
        int number = scanner.nextInt();
        int count;
        for (int i = 2; i<=(number); i++) {
            count = 0;
            while (number % i == 0) {
                number /= i;
                count++;
                if (count == 0) {
                    continue;
                }
            }
            System.out.println(i+ "**" + count);
        }
    }
}

The problem I have right now is that whenever I run it with, like, the number 15453, I get a list of every factor from 1 to 100 and its exponent when I only want the prime factors, and I'm stuck as to how to proceed.

Answer

Sergey Kalinichenko picture Sergey Kalinichenko · Sep 24, 2012

You are almost there! Move the if-continue block outside the for loop. Otherwise, it "continues" the inner-most loop, rather than the one you intended.

while (number % i == 0) {
    number /= i;
    count++;
}
if (count == 0) {
    continue;
}
System.out.println(i+ "**" + count);

Alternatively, you could enclose the System.out.println call in if (count != 0), because it's the only statement following the continue:

while (number % i == 0) {
    number /= i;
    count++;
}
if (count != 0) {
    System.out.println(i+ "**" + count);
}

Your program on ideone: link.