Why is my array showing 0s when I flip it and reverse it?

Question

Trying to reverse an user-input array.

My code

    Scanner s = new Scanner(System.in);
    System.out.println("Enter numbers: ");
    int[] array = new int[5];
    int[] reversed = new int[array.length];
    for (int i = 0; i < array.length; i++) {
        array[i] = s.nextInt();
        reversed[i] = array[array.length - 1 - i];
    }
    System.out.println(Arrays.toString(reversed));

When I enter:

 10
 20
 30
 40
 50

I get:

 output:
 [0, 0, 30, 20, 10]

Yet when I hardcode numbers, it works just fine.

  int[] array = {10, 20, 30, 40, 50};
    int[] reversed = new int[array.length];
    for (int i = 0; i < array.length; i++) {
        reversed[i] = array[array.length - 1 - i];
    }
    System.out.println(Arrays.toString(reversed));

I get back:

 [50, 40, 30, 20, 10]

Not sure what I'm doing wrong here. I know there are other ways to do the same thing but I'm trying to figure out why the way I'm doing it is giving me issues.

Answer 1

You are filling your arrays from beginning to end, and you are filling reversed with values from array , before they were populated!

Specifically, once you try to fill reversed[0] , you use array[4] , which was not populated yet.

You can overcome it, by first filling array , and start filling reversed in a second loop after the first is complete.

Answer 2

just change this line:

 reversed[i] = array[array.length - 1 - i];

to:

 reversed[array.length-1-i] = array[i];

as noted you are trying to access array before it is filled

Answer 3

Try the below code to implement the reversal of the array:

import java.util.Scanner;
import java.util.Arrays;


public class Main {
    
    public static void main(String args[]) { 
        
        Scanner s = new Scanner(System.in);
        System.out.println("Enter numbers: ");
        int[] array = new int[5];
        int[] reversed = new int[array.length];
        for (int i = 0; i < array.length; i++) {
            array[i] = s.nextInt();
        }

        int j = array.length; 
        for (int i = 0; i < array.length; i++) { 
            reversed[j - 1] = array[i]; 
            j = j - 1; 
        } 

        System.out.println("Reversed array is: \n"); 
        for (int k = 0; k < array.length; k++) { 
            System.out.println(reversed[k]); 
        } 
    } 
}

Output:

Enter numbers:                                                                                                                                                
1                                                                                                                                                             
2                                                                                                                                                             
3                                                                                                                                                             
4                                                                                                                                                             
5                                                                                                                                                             
Reversed array is:

5                                                                                                                                                             
4                                                                                                                                                             
3                                                                                                                                                             
2                                                                                                                                                             
1