将数组作为用户输入，output 累计和作为新数组

Question

I can't get this program to work. It's supposed to take an array as input and output a new array with the accumulative sum of the input array. I used a function for this (bottom part).

For example:

Input: 1 2 3 4
Output: 1 3 6 10

Here's my program:

import java.util.Scanner;

public class Accumulate {
    public static void main(String[] args) {
        int n, sum = 0;
        Scanner s = new Scanner(System.in);

        System.out.print("Enter the size of the array:");
        n = s.nextInt();
        int a[] = new int[n];

        System.out.println("Enter all the elements:");
        for (int i = 0; i < n; i++) {
            a[i] = s.nextInt();
        }
        System.out.println(Arrays.toString(accSum(a)));
        s.close();
    }

    public static int[] accSum(int[] in) {
        int[] out = new int[in.length];
        int total = 0;
        for (int i = 0; i < in.length; i++) {
            total += in[i];
            out[i] = total;
        }
        return out;
    }
}

Answer 1

Use Arrays.toString() to print an array.

You can't call System.out.println(accSum(a)); directly as that will print the memory address of the array and not the contents. Wrap the call with Arrays.toString(accSum(a)) and it will print the expected output.

PS: The code in your post doesn't compile:

• scanner.close(); should be s.close();
• accSum() should be static.

Addendum: So your full code became this:

public static void main(String[] args) {
    int n, sum = 0;

    Scanner s = new Scanner(System.in);

    System.out.print("Enter the size of the array:");
    n = s.nextInt();
    int a[] = new int[n];

    System.out.println("Enter all the elements:");
    for (int i = 0; i < n; i++) {
        a[i] = s.nextInt();
    }
    System.out.println(Arrays.toString(accSum(a)));

    s.close();
}

public static int[] accSum(int[] in) {
    int[] out = new int[in.length];
    int total = 0;
    for (int i = 0; i < in.length; i++) {
        total += in[i];
        out[i] = total;
    }
    return out;
}

Answer 2

You can use Arrays.stream(int[],int,int) method to get the sum of the previous array elements:

public static void main(String[] args) {
    int[] arr1 = {1, 2, 3, 4};
    int[] arr2 = accSum(arr1);
    System.out.println(Arrays.toString(arr2));
    // [1, 3, 6, 10]
}

public static int[] accSum(int[] arr) {
    return IntStream
            // iterate over the indices of the array
            .range(0, arr.length)
            // sum of the current element and all previous elements
            .map(i -> arr[i] + Arrays.stream(arr, 0, i).sum())
            // return an array
            .toArray();
}

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^{See also: Modifying a 2D array}