Problem with two-dimensional array and for-loop

Question

Today I restarted coding after a few months and tried do do Snake in the console. I tried to do it with a two-dimensional array and 2 for-loops.

public static void clearWindow() {
    String[][] board = new String[9][]; {
        for(int i=0; i<8; i++) {
            for(int o=0; 0<8; o++) {
                board[i][o]="O ";
                System.out.print(board[i][o]);
            }
            System.out.println("");
}}}

The Code has 2 mistakes which I can't find. The first one happens after 10 'O's are printed. It has something to do with board[i][o]="O ";

The second mistake is the System.out.println(""); . With this line, the code won't even run.

Aalexander · Accepted Answer · 2021-02-12 13:11:20Z

1

You have written 0 < 8 and not o < 8 in the condition of the inner loop. Zero will always be smaller than 8 that's why you end up in an endless loop and that's why your second Sysout will never get reached.

I would recommend using the well known names for running variables i for the outer loop and j for the inner one.

edited Feb 12, 2021 at 13:11

answered Feb 12, 2021 at 13:04

Aalexander

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Nowhere Man · Accepted Answer · 2021-02-12 14:25:58Z

Apart from the typo in the loop for(int o=0; 0<8; o++) there are other issues:

2D array board is not initialized properly which causes NullPointerException in line board[i][o]="O ";
Unneeded statement block after initialization of board
Actual dimensions of the board should be used in the loops.
You seem to be creating a "clean" window, so you should return the board from this method. That being said, the code may be changed like this:

public static String[][] clearWindow() {
    String[][] board = new String[9][9];
    for(int i = 0; i < board.length; i++) {
        for(int j = 0; j < board[i].length; j++) {
            board[i][j]="O ";
            System.out.print(board[i][j]);
        }
        System.out.println();
    }
    return board;
}

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