Question

I have no idea why my second for loop won’t execute.. It compiles but when I run this it does not work ~_~

import java.util.Scanner;

public class ranges
{


 public static void main (String[] args)

  {

 Scanner scan = new Scanner (System.in);

       int size;
       int input;
       int count = 0;
       int occurence = 0;
       System.out.print ("Please enter the size of your array: ");
       size = scan.nextInt();
       int[] list = new int[size];



       for (int index = 0 ; index < list.length ; index++)
       {
           System.out.print ("Please enter an integer between 0 to 50: ");
           input = scan.nextInt();

           if ( input >= 0 && input <= 50 )
           {
               list[index] = input;
            }
           else
           {
               System.out.println ("Invalid output, please try again");
               index--;
           }
        }




       int right = (list.length)-1;
       int left = 0;

        for (int counter = left ; counter < list.length ; counter++)
        {
            while ( right >= left )
            {
                if ( list[left] == list[right] )
                {
                    occurence++;
                    right--;
                }
            }
           right = (list.length)-1;
           System.out.println ("The number " + list[left] + " was added " + occurence + "4 times");
        }

         for (int value : list)
        {
            System.out.print (value + " ");
        }
       ;








    }
}

My updated for loop to evaulate occurences

for (int left = 0 ; left < list.length ; left++)

{

        while ( right >= left )
        {
            if ( list[left] == list[right] )
            {
                occurence++;

            }
            right--;
        }


       System.out.println ("The number " + list[left] + " was added " + occurence + " times");
       right = (list.length)-1;
       occurence = 0;
    }

I have cleaned it up a bit, and now occurences are same as the inputs

Answer 1

You second for is also working. The problem is in while loop condition i.e. while ( right >= left ). If list[left] == list[right] is not equal, it goes in infinite loop as neigther right nor left changing in that case.

I think, you need to change your while as below(move right-- outside the if condition):

  while ( right >= left )
   {
     if ( list[left] == list[right] )
      {
        occurence++;
      }
      right--;
    }

Two more issues:

Please re-initialize occurence =0; before the while loop so that it counts occurence of each number and remove 4 from your System.out.println() e.g. below:

for (int counter = left ; counter < list.length ; counter++)
{ 
  occurence = 0; //< initialize to 0
  while ( right >= left )
  {
      if ( list[left] == list[right] )
      {
         occurence++;
       }
           right--;
   }
   right = (list.length)-1;
       //remove 4 after "occurance +"
   System.out.println ("The number " + list[left] + 
                                            " was added " + occurence + " times");
 }

EDIT: working sample with HashMap:

       Map<Integer, Integer> scannedNums = new HashMap<Integer, Integer>();
        for (int counter = left ; counter < list.length ; counter++)
        {
            if(scannedNums.get(list[counter]) == null){
                scannedNums.put(list[counter], 1);
            }else{
                int currentCount = scannedNums.get(list[counter]);
                scannedNums.put(list[counter], currentCount+1);
            }
        }

        Set<Integer> nums = scannedNums.keySet();
        Iterator<Integer> numIter = nums.iterator();
        while(numIter.hasNext()){
            int number = numIter.next();
            System.out.println ("The number " + number + 
                    " was added " + scannedNums.get(number) + " times");
        }