Arrays and output

Question

I'm new to programming with java, so please be lenient with my silly errors. My problem is that my code isn't giving the output that I desire, which is to display all the even values of an array underneath each other and then all the uneven values of the array under each other. This is my code:

//main class
public class Even_number_array
{

  public static void main(String[] args)
  {

    array_class obj = new array_class();
    obj.set_numbers();
  }
}

//another class
public class array_class
{

  private int arr[] =
  {
    10, 20, 7, 8, 3, 6, 11, 9, 7, 45
  };

  public void set_numbers()
  {

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

      if (arr[i] % 2 == 0)
      {
        System.out.println("These even numbers were found in the array:");
        do
        {
          System.out.println(arr[i]);
          i++;
        }
        while (arr[i] % 2 == 0);
      }
      else if (arr[i] % 2 != 0)
      {
        System.out.println("uneven numbers found in array:");
        do
        {
          System.out.println(arr[i]);
          i++;
        }
        while (arr[i] % 2 != 0);
      }

    }

  }
}

And this is my output (using Netbeans IDE which shows the errors I have, which I have included because I don't quite understand what it means.):

These even numbers were found in the array:

10

20

These even numbers were found in the array:

Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: 10

8

These even numbers were found in the array:

6

uneven numbers found in array:

9

7

45

at even_number_array.array_class.set_numbers(array_class.java:35)

at even_number_array.Even_number_array.main(Even_number_array.java:12)

Java Result: 1

I have a few questions, why is the number 8 in my array not printing with 10 and 20, and 6 printing separately like 8? And also, is there a way that I can get user input using the Scanner class for the array and how would I go about doing this?

Any help would be welcomed! Thanks in advance :)

Answer 1

For loop should be < not <=.

System.out.println("Even Numbers");
for (int i=0; i < arr.length;i++){
   if((arr[i] % 2) == 0)
   {
      System.out.println(arr[i]);
   }
}
System.out.println("Odd Numbers");
for (int i=0; i < arr.length;i++){
   if((arr[i] % 2) != 0)
   {
      System.out.println(arr[i]);
   }
}

---

ArrayList<Integer> array = new ArrayList<Integer>();
        int[] intArray;
        Scanner scanner = new Scanner(System.in);
        int a = 0;
        while(a != -1)
        {
            System.out.println("Please enter an integer -1 to quit: ");
            a = scanner.nextInt();
            if(a != -1)
            {
                array.add(a);
            }
        }
        intArray = new int[array.size()];
        for(int i = 0; i < array.size(); i++)
        {
            intArray[i] = array.get(i);
        }
        for(int b = 0; b < intArray.length; b++)
        {
            System.out.println("Integer" + b + ": " + intArray[b]);
        }

Put this code in your main method and execute. I hope this helps you with your problem.

Answer 2

If I understand your question - and what you want. The easiest solution (I see) is to loop twice,

// Print the even numbers first.
for (int i=0; i < arr.length;i++){
  if (arr[i] % 2 == 0) { // % 2 == 0 is even
    System.out.printf("arr[%d] = %d%n (even)", i, arr[i]);
  }
}
// Then the odd numbers.
for (int i=0; i < arr.length;i++){
  if (arr[i] % 2 != 0) { // % 2 != 0 is odd (or "uneven")
    System.out.printf("arr[%d] = %d%n (odd)", i, arr[i]);
  }
}

Answer 3

To answer your question : "why is the number 8 in my array not printing with 10 and 20, and 6 printing separately like 8?"

It's because of your 2 loops system (for + do while). For example, at the time you print "20" with i = 1, then you do a i++ giving you i = 2 and arr[i] = 7. At this moment, you have a test in your while arr[i]%2==0 and of course 7%2 != 0 so you exit your do while loop, go back to the for, DO ANOTHER i++ giving you i = 3 and then go to your if again : in this example you have never printed the value arr[2] = 7 and you print again "These even numbers were found in the array:" with the value arr[3] = 8.

I hope the explanation is clear enough. It's quite tough to explain algorithm without a white board ;)

PS : +1 for the "For loop should be < not <=" in this case.