2d array help

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

Code:

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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 = 0; i < rows; i++) {
                        for (int j = 0; j < columns; j++) {
 
                                board[rows][columns] = false;
 
                        }
                }
 
                for (int i = 0; i < rows; i++) {
                        for (int j = 0; j < columns; j++) {
 
                                if(board[rows][columns] == false) {
                                        System.out.print("-");
 
                                }
 
                        }
                        System.out.println();
                }
        }
}

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Why i and j are initialized to 1?

Code:

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for (int i = 1; i < rows; i++) {
            for (int j = 1; j < columns; j++) {

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I don't see any random value in code above.

Good call. I switched them to 0 but it still gives me this error: Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException

How do You access element of an array?

Quote:

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Originally Posted by nweid1

Code:

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for (int i = 0; i < rows; i++) {
                        for (int j = 0; j < columns; j++) {
 
                                board[rows][columns] = false;
 
                        }
                }

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Firstly it is not always possible that the user is going to input same number of rows and columns i.e. it can be a irregular 2-dimensional array, therefore
you cannot write your inner for-loop the way you have written. More better way is

Code:

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for(int i=0; i< rows; i++)
          {
              for(int j=0; j<board[i].length; j++)
              { 
                        //code
              }
          }

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Secondly as said previously by dragon you are accessing your array elements incorrectly inside the for loop, it has to be

Code:

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board[i][j]

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instead of

Code:

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board[rows][columns]

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Quote:

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Originally Posted by Rameshwar Soni

Firstly it is not always possible that the user is going to input same number of rows and columns i.e. it can be a irregular 2-dimensional array, therefore
you cannot write your inner for-loop the way you have written. More better way is

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It's called rugged array.

The question originally posted by user will not have the irregular 2 dimensional array. So the for-loops used by the original user will work but will fail
if he goes for irregular multi-dimensional array.

Quote:

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Originally Posted by diamonddragon

It's called rugged array.

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Do you mean to say Jagged array, which is there in C-sharp?:)-: