My code to access elements of array using for loop. The output of the program is [19,17,15] which are the elements of array int a[] = { 12, 15, 16, 17, 19, 23 }. Output after following code is written:

public class Tester {
    public static void main(String s[]) {
        int a[] = { 12, 15, 16, 17, 19, 23 };
        for (int i = a.length - 1; i > 0; i--) {
            if (i % 3 != 0) {
                --i;
            }
            System.out.println(a[i]);
        }
    }
}

Algorithm:

1. Iteration 1: i=5 so a[5]=23. "if statement" gets true and --i execute. so i=4. Hence, a[4]=19 will get print as first element in output.

2. Iteration 2: i=3 so a[3]=17. "if statement" gets true again and --i should execute but it skips that condition as I tried using debugging tool to see how it is working. And output is a[3]=17 which is wrong I think.

Could you help me in understanding why it gives 17 as output? As in my opinion it should skip that part.

CodePudding user response：

Here is a step by step explanation. (i % 3 != 0) checks to see if i is not divisible by 3. Also note that in this context, your post and pre-decrements of i are not relevant as the outcome would be the same no matter how they are decremented.

 i = 5;
 i not divisible by 3 so i-- = 4
 print a[4] = 19
 i-- at end of loop = 3
 i is divisible by 3 so i remains 3
 print a[3] = 17
 i-- at end of loop = 2
 i not divisible by 3 so i-- = 1
 print a[1] = 15
 i-- = 0 so loop terminates.

CodePudding user response：

In iteration 2, where i=3 the condition is false, since 3 % 3 = 0