Finding sum of rows of 2D array, using 1 loop in java

Question

int[][] arr = { { 11, 12, 13, 14, 15, 16 }, 
            { 21, 22, 23, 24, 25, 26 }, 
            { 31, 32, 33, 34, 35, 36 },
            { 41, 42, 43, 44, 45, 46 }, 
            { 51, 52, 53, 54, 55, 56 }, 
            { 61, 62, 63, 64, 65, 66 } };
    int sum = 0;
    int rowsSum = 0;
    int rowIndex = 0;
    for (int i = 0; i < arr.length * arr.length; i++) {
        System.out.print(arr[i / arr.length][i % arr.length] + " ");
        sum += arr[i / arr.length][i % arr.length];
        if (i % 6 == 0) {
            System.out.println();
            System.out.println("Sum of row " + (rowIndex + 1) + " is: " + sum);
            rowsSum += sum;
            sum = 0;
            rowIndex++;
        }

    }
    System.out.println();
    System.out.println("Sum of all rows is: " + rowsSum);    

This is what I've written so far. The problem I encounter is that i is 0 at the first iteration making i%6=0 as well and making it so that row 1 consists of arr[0][0] only and each next row ends with the actual first of the next one.

I have a feeling the solution must be easy but I haven't found one for the past hour or so. Any help would be appreciated.

Answer 1

Instead of comparing i%6 to zero, compare it to 5, the last number before the remainder drops to zero again. This would let you do the output when you reach the last element of the current row, rather than waiting to reach the initial element of the next row (and dropping the printout for the last row altogether).

if (i % 6 == 5) {
    System.out.println();
    System.out.println("Sum of row " + (rowIndex + 1) + " is: " + sum);
    rowsSum += sum;
    sum = 0;
    rowIndex++;
}