Counting number of digits in integer

Question

My code is supposed to prompt the user for an integer and count the occurrences of each digit in the integer. But it outputs nothing. Please help and here's my code.

import java.util.Scanner;

    public class NumberCounts {

    public static void main(String [] args) {
         Scanner scan = new Scanner(System.in);

         int arr [] = new int [10];
         int num;
         int outcome;

         System.out.println(" Enter a number: "); 
         num = scan.nextInt();

         while ( num != 0){
             outcome = num % 10;
             arr[num % 10]+=1;
             num /= num;
         }

         for ( int i = 0; i <= arr.length; i++){
             System.out.println(i + " : " + arr[i]);
         }

     }
}

`num /= num`?? Anything divided by itself is 1. And 1 is never equal to 0, so your loop isn't going to exit. — azurefrog, May 22 '18 at 21:27
A debugger would find this sort of thing very quickly, if the OP would just use one. — markspace, May 22 '18 at 21:28
See also [What causes a java.lang.ArrayIndexOutOfBoundsException and how do I prevent it?](https://stackoverflow.com/q/5554734/1553851) — shmosel, May 22 '18 at 21:30
Enter a number: 45544 0 : 0 1 : 0 Exception in thread "main" 2 : 0 3 : 0 4 : 3 5 : 2 6 : 0 7 : 0 8 : 0 9 : 0 java.lang.ArrayIndexOutOfBoundsException: 10 at NumberCounts.main(NumberCounts.java:41) — calvin jackson, May 22 '18 at 21:30
Converting the int to String and processing that one could be easier I guess — Marged, May 22 '18 at 21:32

score 3 · Accepted Answer · answered May 22 '18 at 21:31

Inside your while loop, you are dividing num by itself, then assigning the result back to num. This will make num equal to 1 forever. Change it to

num /= 10;

which will remove the last digit.

Also, you already calculated the last digit and stored the result in outcome. You might as well use it:

arr[outcome]+=1;

Then, when you get to the loop to print the array, in the condition, always use < an array length to stop after processing the last index length - 1. This will prevent the ArrayIndexOutOfBoundsException that is waiting to show up.

for (int i = 0; i < arr.length; i++){

Counting number of digits in integer

1 Answers1