Question

I have a problem with an (I guess) simple Java program. I need to create a two-dimensional array (that is called a “matrix”, right?) which should look like this:

1 2 3 4  5  6  7  8  9 10   (1st row)
3 4 5 6  7  8  9 10 11 12   (2nd row)
6 7 8 9 10 11 12 13 14 15   (3rd row)
...

As you can see, the 1st row is 1, 2, 3, …; the 2nd row is the 1st row with the 2nd row’s row index added to each element. And so on: Every row is the previous row + the current row’s row number (1-based).

Answer 1

First define the number of columns and rows, and instantiate the array:

int columns = 10, rows = 3;
int[][] myArray = new int[rows][columns];

Then do a loop for every row, and inside that loop, loop for every column, let’s say you call the outer loop counter i and the inner loop counter j. Then you can assign a value in the array using this formula:

myArray[i][j] = j + ( (i+1) * (i+2) ) / 2;

This formula assumes 0 <= i < rows and 0 <= j < columns