How to count and list odd numbers in an array

Question

public class OddsAndEvens {

    // counts all the odd numbers in the array
    private static int countOdds(int[] array) {
        int count = 0;

        for(int i = 0; i < array.length; i++) {
            if(array[i] % 2 == 1 && array[i] % 2 != 0) {
                count++;

            }
        }
        return count;

    }

    // returns an array with all the odd numbers
    public static int[] getAllOdds(int[] array) {
        int[] yaArray = new int[countOdds(array)];
        int j = 0;

        for(int i = 0; i < array.length; i++) {
            if(array[i] % 2 == 1 && array[i] % 2 != 0) {
                yaArray[j] = array[i];

            }
            j++;

        }
        return yaArray;

    }
}

///////////////////////////////////////////////////////////
runner code

public class OddsAndEvensRunner {

    public static void main(String args[]) {
        System.out.println("Odds - " + Arrays.toString(OddsAndEvens.getAllOdds(new int[]{2,4,6,8,10,12,14})));
        System.out.println("Evens - " + Arrays.toString(OddsAndEvens.getAllEvens(new int[]{2,4,6,8,10,12,14})));
        System.out.println("\nOdds - " + Arrays.toString(OddsAndEvens.getAllOdds(new int[]{1,2,3,4,5,6,7,8,9})));
        System.out.println("Evens - " + Arrays.toString(OddsAndEvens.getAllEvens(new int[]{1,2,3,4,5,6,7,8,9})));
        System.out.println("\nOdds - " + Arrays.toString(OddsAndEvens.getAllOdds(new int[]{2,10,20,21,23,24,40,55,60,61})));
        System.out.println("Evens - " + Arrays.toString(OddsAndEvens.getAllEvens(new int[]{2,10,20,21,23,24,40,55,60,61})));

    }
}

Ignore code relating to evens. When run the odd array only lists out one odd number instead of the others inside of the first array along with a couple of zeros. I tried a lot of things but simply won't count all of the odd numbers.

The second part of this `if(array[i]%2==1 && array[i]%2!=0)` is redundant isn't it? — Scary Wombat, Oct 17 '17 at 02:00
Step through the execution of your program using your debugger. (And I suspect that you will find that `j++` is outside your `for` loop in `getAllOdds()`, despite what it looks like.) — dave, Oct 17 '17 at 02:01
`return IntStream.of(array).filter(i -> i % 2 != 0).toArray();` — Elliott Frisch, Oct 17 '17 at 02:09

score 3 · Answer 1 · answered Oct 17 '17 at 02:03

Take a look at this part:

public static int[] getAllOdds(int[] array) // when 
{
    int[] yaArray = new int[countOdds(array)];
    int j = 0;
    for(int i = 0; i<array.length;i++)
        if(array[i]%2==1 && array[i]%2!=0)
            yaArray[j]=array[i];
            j++;
    return yaArray;
}

The variable j is incremented only once, which is after the loop ends. If you have multiple statements to be executed in looping or conditional branch, use brackets.

Also array[i]%2==1 means the same thing as array[i]%2!=0, so can eliminate one of them.

public static int[] getAllOdds(int[] array) // when 
{
    int[] yaArray = new int[countOdds(array)];
    int j = 0;
    for(int i = 0; i<array.length;i++)
    {
        if(array[i]%2==1)
        {
            yaArray[j]=array[i];
            j++;
        }
    }
    return yaArray;
}

Might be good to advice OP to always use braces https://stackoverflow.com/questions/8020228/is-it-ok-if-i-omit-curly-braces-in-java — Oleg, Oct 17 '17 at 02:14
According to [Google Java Style Guide](https://google.github.io/styleguide/javaguide.html#s4.1.1-braces-always-used), braces are used with if, else, for, do and while statements, even when the body is empty or contains only a single statement. — LHCHIN, Oct 17 '17 at 02:41

score 0 · Answer 2 · answered Oct 17 '17 at 12:25

Use List instead of Arrays. List is better to use.

Try like this,

public static void main(String[] args) {
    System.out.println("Odds - " + Arrays.toString(getAllEvens(new int[] { 1, 2, 3, 4, 5, 6, 7, 8, 9 })));
    System.out.println("Evens - " + Arrays.toString(getAllOdds(new int[] { 1, 2, 3, 4, 5, 6, 7, 8, 9 })));
}

public static Object[] getAllOdds(int[] array) {
    List<Integer> list = new ArrayList<>();
    for (int no : array) {
        if (no % 2 != 0)
            list.add(no);
    }
    return list.toArray();
}

public static Object[] getAllEvens(int[] array) {
    List<Integer> list = new ArrayList<>();
    for (int no : array) {
        if (no % 2 == 0)
            list.add(no);
    }
    return list.toArray();
}

You can also return list instead of list.toArray() for better list.

How to count and list odd numbers in an array

2 Answers2