我怎样才能得到一个数组的总和？

Question

I'm trying to sum up all of the elements in an array. What do I need to put in for blank space of int i = ______; to make this work?

public static int sumArray(int [] A){

        int sum = 0;
        int i = ___________ ;
        while(i>=0){
            sum = sum + A[i];
            i--;
        }return sum;

    }

Answer 1

I'm trying to sum up all of the elements in an array. What do I need to put in for blank space of 'int i = ______;' to make this work?

You should specify the size of array A to i by doing i = A.length - 1; .

Alternatively, you can use a for loop instead of while .

Here is the code snippet:

public static int sumArray(int [] A){
    int sum = 0;
    for(int x : A) {
        sum += x;
    }
    return sum;
}

Answer 2

To answer your question, you should set int i to A.length - 1 . You want length - 1 because Arrays are indexed at 0 which means using length alone will cause you an IndexOutOfBoundsException .

Your method should look like this:

public static int sumArray(int[] A) {
    int sum = 0;
    int i = A.length - 1;
    while (i >= 0) {
        sum = sum + A[i];
        i--;
    }
    return sum;
}

However , you can do this in much more cleaner ways.

1) Using Java 8 you can use IntStream like so:

public static int sumArray(int[] A) {
    return IntStream.of(A).sum();
}

2) You can use a for loop:

 public static int sumArray(int[] A) {
    int sum = 0;
    for(int i = 0; i < A.length; i++){
      sum += A[i];
      }
     return sum;
 }

3) You can use an enhanced for loop:

public static int sumArray(int[] A) {
    int sum = 0;
    for(int i : A){
        sum += i;
    }
    return sum;
}

Answer 3

You've already written the code to get the sum. i just needs to start out at A.length .

There are many other ways to get the sum: using an enhanced "for each" loop; using IntStream.of(A).sum() ; other library methods.