Thread: help factor

public class Factor {
 
	public static void main(String[] args){
            Scanner input=new Scanner (System.in);
 
	   String yn;
	   int number;
	   int current;
	   String output = "";
	   int x;
	   int i = 2;
 
	  System.out.print("Enter a number to factor : ");
          number = input.nextInt();
 
 
 
 
	   while (number % 2 == 0)
           {
	      output += 2 +" ";
	      number /= 2;
            }
 
	   x = number;
 
	   while (i <= x)
	   {
	      if (number % i == 0)
	      {
	         output += i + " ";
	         x /= i;
 
 
	      }
	      i++;
           }
 
 
 
          System.out.println("Factors are : " + output);
          System.out.println();
          System.out.print("Do you wish to do another (Y/N)? : ");
          //havent finished this part yet
 
	}
}

i have this code which asks the user to enter a number and outputs the factors.....

but say the user enters 120... it should displey 2 2 2 3 5 but it only displays 2 2 2... help

public class Factor {
 
	public static void main(String[] args){
            Scanner input=new Scanner (System.in);
 
	   String yn;
	   int number;
	   int current;
	   String output = "";
	   int x;
	   int i = 2;
          char c = 'c';
	  System.out.print("Enter a number to factor : ");
          number = input.nextInt();
 
boolean repeat = true;
boolean isValid = false;
 
while (repeat == true)
{
 
 
 
	   while (number % 2 == 0)
           {
	      output += 2 +" ";
// output = output.concat(2 + " "); works too I think
 
	      number /= 2;
            }
 
	   x = number;
 
	   while (i <= x)
	   {
	      if (number % i == 0)
	      {
	         output += i + " ";
	         x /= i;
 
 
	      }
	      i++;
           }
 
 
 
          System.out.println("Factors are : " + output);
          System.out.println();
while (isValid ==false)
{
          System.out.print("Do you wish to do another (Y/N)? : ");
c = input.next().charAt(0);
         if (c == 'y' || c== 'Y')
{
repeat = true;
isValid = true;
}
 
else if (c == 'n' || c == 'N')
{
repeat = false;
isValid = true;
 
}
 
else
{
System.out.println("Enter a y or n");
isValid = false;
}
}
}
 
 
	}
}

It appears that my while loops, while letting you repeat, don't clear the value in output.

Also, your code may not work for 121.

It appears to work for 120.

If I knew what would work, I'd save it to add to my own code to check to see if a number if a prime number and if it is odd or even. I'd have to change it since I was using longs in that one, but still.

I found a way to figure out the, unsimplified, factors of a number:

import java.util.*;
 
 
public class Factor2 {
 
 
	public static void main(String[] args)
	{
		Scanner console = new Scanner(System.in);
		int number = 0;
	ArrayList<Integer> aList = new ArrayList<Integer>();
 
	System.out.println("Enter a number to factor");
	number = console.nextInt();
 
	for (int num = 1; num <= number; num++)
	{
		if (number%num ==0)
			aList.add(num);
	}
 
	String output = aList.toString();
	System.out.println("The factors are: " + output);
	}
}

As for the glitch in my other code where it kept adding on, just add
output = "";
under

if (c== 'Y' || 'y')

However, for 121

Your code still says

output is 11.

It should say

ouput is 11 11

Originally Posted by gonfreecks

oh yeah my bad it runs 2 2 2 3 5 but if i run 150 it only runs 2 3 5 while it needs to output 2 3 5 5..

thanks for the help

Shot in the dark, since I'm just sort of walking through, but if you are not getting the last number each time, check to see if you exit the loop too early. It is a fairly common issue that you probably will never get over doing (I still do that sort of thing often enough).

*continues walking*

Originally Posted by gonfreecks

oh yeah my bad it runs 2 2 2 3 5 but if i run 150 it only runs 2 3 5 while it needs to output 2 3 5 5..

thanks for the help

The reason that is happening is because after you find out 5 is a factor of x, you are dividing x by 5, and then incrementing i to 6. This is where it is broken, because the new value of x is also divisible by 5.

You can solve this very easily, by checking if it is still divisible by i, and if so, decrementing i, before it gets incremented, so it will check that value of i again.

Here is the code you originally posted, with a slight modification:

import java.util.Scanner;
 
public class Factor {
 
	public static void main(String[] args){
		Scanner input=new Scanner (System.in);
 
		String yn;
		int number;
		int current;
		String output = "";
		int x;
		int i = 2;
 
		System.out.print("Enter a number to factor : ");
		number = input.nextInt();
 
 
 
 
		while (number % 2 == 0)
		{
			output += 2 +" ";
			number /= 2;
		}
 
		x = number;
 
		while (i <= x)
		{
			[B]if (number % i == 0)[/B]
			{
				output += i + " ";
				x /= i;
				//I added from here
				if(x % i == 0){
					i--;
				}
				//to here
			}
			i++;
		}
 
 
 
		System.out.println("Factors are : " + output);
 
	}
}

There are still problems with this code by the way. I bolded the problem area.... I'll leave it up to you to fix it (should be a very obvious and quick fix.)