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Thread: Printing 2d array

  1. #1

    Default [Solved] Printing 2d array

    I have to write a program for my programming class prints out a table filled with "-"s and randomly fills them with "#"s. So first, I have to create a 2d array where the number of rows and columns are given by the user. Then, I have to print the initial table with all "-"s. So, I created a boolean array with the number of rows and columns as the user input, and make a for loop to set every spot in the array as false. Then I may a loop that says if the spot is false, print out a "-". If I enter a number over 1 for the column or row, it won't work. If I put 1, it runs but doesn't print out. Please help! What am I doing wrong? A sample of the output would be:

    Rows: 5
    Columns: 8

    - - - - - - - -
    - - - - - - - -
    - - - - - - - -
    - - - - - - - -
    - - - - - - - -

    Heres the code

    public class Matrix2 {
    import java.util.Random;
    import java.util.Scanner;
    	public static void main(String[] args) {
    		Scanner console = new Scanner(System.in);
    		System.out.println("Number of rows?");
    		int rows = console.nextInt();
    		System.out.println("Number of columns?");
    		int columns = console.nextInt();
    		boolean board[][] = new boolean[rows][columns];
    		for (int i = 1; i < rows; i++) {
    			for (int j = 1; j < columns; j++) {
    				board[rows][columns] = false;
    		for (int i = 1; i < rows; i++) {
    			for (int j = 1; j < columns; j++) {
    				if(board[rows][columns] == false) {
    Last edited by nWeid1; January 29th, 2012 at 08:42 PM.

  2. #2

    Default Re: Printing 2d array

    I think you need to think about what you want your loops to do. You want something to change every time you go iterate through the loop, but the way you have it set up right now, nothing does. Also, you want to make sure you initialize your loop pointers at 0 instead of 1.

  3. #3

    Default Re: Printing 2d array

    Well, the first loop can be deleted for now. At this point in time, I just want to print out a table of -'s of a given number of rows and columns and isn't that what the second loop does? It starts at row 1 and increases by 1 until it hits the row the user gave which is given by the variable rows. Then it goes through every column and prints out a -.

  4. #4

    Default Re: Printing 2d array

    Remember that you should not use an equality test for pbooleans, but rather use the built-in expression.

    For example, if you were checking if board[rows][columns] was false, you should use this :


    However, another thing you want to note is that you don't want to use
    [code=Java]boards[rows][columns][/code] in your loop, but rather use your loop counters, EG

  5. #5

    Default Re: Printing 2d array

    Tjstretch, I am an idiot for using board[rows][columns] and not boards[i][j] lol thanks for pointing out the obvious. And thanks for the !board[][] tip. It's working now, thanks!

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