Creating an array method java

Question

Here I need to write a method called powArray that takes a double array a and returns a new array that contains the elements of a squared. Generalize it to take a second argument and raise the elements of a to given power. I tried to write it, but got 0 result, can someone write this and explain how it work, so I could write it in future.

public class Task {
    public static void main(String[] args) {

    }

    public static double powArray (double a[]){
        for (int i = 1; i < a.length; i++) {
            a[i] = Math.pow(a[i], 2.0);
            System.out.print(a[i]);
            return powArray(a);
        }
        return -1;
    }
}

Also, after compile got nothing, only clear console w/o any numbers, etc.

hey there is a error in your code java method could not return more than once as in your code. — bit-shashank
– bit-shashank, Commented May 7, 2017 at 14:09
you are not returning an Array, rather you are modifying the current array in the first place, and also at first look i would see that this method never returns because of recursion — Hallow
– Hallow, Commented May 7, 2017 at 14:10
You start by changing your return type from double to array of double. Then you read your books again on creating and iterating arrays. And no, I will not do more of your homework for you; and I hope nobody else does. — GhostCat
– GhostCat, Commented May 7, 2017 at 14:11
Some guidelines just to help you. 1 - Create a new array of doubles with the same size of the array received in parameter. 2 - Change return type to array of doubles 3 - for each item in the receiving array insert its powered value in the created array to return 4 - lastly return the created array — Hallow
– Hallow, Commented May 7, 2017 at 14:14

Sourav Sachdeva · Accepted Answer · 2017-05-07 14:27:08Z

1

Adding to the Sandeep Kakote's answer :

 public static void main(String[] args) {
            // TODO Auto-generated method stub
            double[] squareArry = powArray(new double[]{10,20,30},3);

        }

        public static double[] powArray (double a[],int z){
            double[] b = new double[a.length];
            for (int i = 0; i < a.length; i++) {
                b[i] = Math.pow(a[i], z);
                System.out.print(b[i]);
            }
            return b;
        }

answered May 7, 2017 at 14:27

Sourav Sachdeva

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Comments

Youcef LAIDANI · Accepted Answer · 2017-05-07 16:33:11Z

1

It seams you are making a recursive method because you call your method in the return return powArray(a);, so this will call your method again and again until your condition is wrong and return -1.

... i need to write a method called powArray that takes a double array, a, and returns a new array

The first part is correct method called powArray that takes a double array, but the second is not return an array it return a double, instead your method signature should look like :

public static double[] powArray (double a[]){
//------------------^^

Now the return part should be like so ;

public static double[] powArray (double a[]){
    for (int i = 0; i < a.length; i++) {
         a[i] = Math.pow(a[i], 2.0);
    }
    return a;//<<-------------return the result
}

Test

If you try to make this call in your main method :

public static void main(String[] args) {
    double[] a = new double[]{5, 6, 8, 7};
    System.out.println(Arrays.toString(powArray(a)));
}

The output :

[25.0, 36.0, 64.0, 49.0]

edited May 7, 2017 at 16:33

answered May 7, 2017 at 14:17

Youcef LAIDANI

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2 Comments

Jurtchak Over a year ago

Thanks a lot, ill take a close look of it. Also my first version of powArray method was same, but the problem was that i didnt know what to write in main method to show reult. Thanks.

Youcef LAIDANI Over a year ago

@Jurtchak note your method is a recursive method note that

Sandeep Kokate · Accepted Answer · 2017-05-07 14:28:03Z

As you said, " i need to write a method called powArray that takes a double array,a, and returns a new array that contains the elements of a squared. " You are need to improve following things,

You are not returning array.
Remove your return statement from for loop, I think you want to try recursion.
If you want to return a new array that contains the squared elements then create a new array in powArray method and copy the squared value and return that array.

Take a following example:

public static void main(String[] args) {
        // TODO Auto-generated method stub
        double[] squareArry = powArray(new double[]{10,20,30});

    }

    public static double[] powArray (double a[]){
        double[] b = new double[a.length];
        for (int i = 0; i < a.length; i++) {
            b[i] = Math.pow(a[i], 2.0);
            System.out.print(b[i]);
        }
        return b;
    }

If you want to use recursion then returning an array not required, because you will change the value of array passed itself. Take a close look of following example with recursion:

public static void main(String[] args) {
        // TODO Auto-generated method stub
        double a[] = new double[]{2,5,4,6};
         powArray(a,0);
        for(double value:a){
            System.out.println(value);
        }

    }

    public static void powArray(double a[], int index) {
        if (index < a.length) {
            a[index] = Math.pow(a[index], 2.0);
            powArray(a, ++index);
        }
    }

Aritra Chatterjee · Accepted Answer · 2017-05-07 14:19:58Z

You can use the following snippet below, but this does not take into consideration your generic case, that you will pass the power, currently it will do for power of 2.

public class Task {
public static void main(String[] args) {
    double[] arr = {2.0,3.0,4.0};
    powArray(arr);
    for(double a : arr){
        System.out.println(a);
    }
}

public static void powArray (double a[]){
    for (int i = 0; i < a.length; i++) {
        a[i] = Math.pow(a[i], 2.0);
    }
}
}

The main method should not be empty as it is the starting point. Since powArray is a static method it can be called directly in your main method. The powArray should return a double array but it is just returning a double Your for loop starts from 1 but goes to arraylength - 1 which will run for n-1 elements instead of n elements Within each loop iteration you are returning and the return statement is making a recursive call(Calling the same method again, which will result in stack overflow)

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