closed and open elements in an array-CodePudding

I am writing a code to indicate open and closed elements in a 2d array. An open element is represented with . and a closed element is represented with *. The first column in the array must be completely open whereas all the other columns must be closed. The output should be:

.**
.**
.**

The array is also going to vary in size as the user will determine how big the array is. I have managed to code a 2D array grid as this is not hard, however, I am trying to now use an if-statement to make the first column all open. I placed the if-statement within the nested loop:

import java.util.Arrays;
import java.util.Scanner;

public class trial {

public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    System.out.println("What size square grid do you want? ");
    int m = sc.nextInt();
    char[][] grid = new char[m][m];
    int i;
    int j;
        for(i=0; i<grid.length; i  ) {
            for(j=0; j<grid[i].length; j  ) {
                grid[i][j] ='.';
                if(grid[j].length > grid[0].length) {
                    System.out.println("");
                }else {
                    System.out.print('*');
                }
                StdOut.print(grid[i][j]);
            }
            StdOut.println();
        }
        
}

}

This, however, is giving me an output that looks like this:

*.*.*.
*.*.*.
*.*.*.
*.*.*.

I have tried placing the if-statement outside of this nested for-loop but I then get an error with my variables as they have not been defined. Any assistance as to how to fix this or make it that I can get values for my i and j variables outside of the for-loop would be greatly appreciated.

CodePudding user response：

I slightly modify your code to make it fit the description.

i and j will vary when the loop proceeds, and should be accessed inside the loop only.

It seems that you want to change the content inside grid, which can be accessed outside the loop after processing.

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        System.out.println("What size square grid do you want? ");
        int m = sc.nextInt();
        char[][] grid = new char[m][m];
        int i;
        int j;
        for (i = 0; i < grid.length; i  ) {
            for (j = 0; j < grid[i].length; j  ) {
                grid[i][j] = '.';
                if(j > 0) {
                    grid[i][j] = '*';
                }
                System.out.print(grid[i][j]);
            }
            System.out.println();
        }

        // you cannot access i/j outside the loop scope. instead, you can access the grid
        System.out.println("Loaded array:");
        Arrays.stream(grid).forEach(System.out::println);
    }

CodePudding user response：

Just check if the current column is 0 or not Just a minor change will work here I am writing only the main loop below

for(i=0; i<grid.length; i  ) {

    for(j=0; j<grid[i].length; j  ) {
       if(j == 0){          //0th column make it dot(.)
          grid[i][j] ='.';
       }
       else {              //For other columns put asterisk(*)
         grid[i][j] = '*';
       }  
   }
}

CodePudding user response：

Here's a different way to think about 2D arrays. They are simply a 1D array where each element is itself another 1D array (a complete "row").

With that in mind, here's a different way to initialize and print the contents of the 2D array using a mixture of enhanced and indexed for loops:

  public static void main(String[] args)
  {
    Scanner sc = new Scanner(System.in);
    System.out.println("What size square grid do you want? ");
    int m = sc.nextInt();
    char[][] grid = new char[m][m];
    
    for(char[] row : grid) {
      for(int col=0; col<row.length; col  ) {
        row[col] = (col == 0) ? '.' : '*';
      }
    }

    for(char[] row : grid) {
      for(char c : row) {
        System.out.print(c);
      }
      System.out.println();
    }
  }

Output:

What size square grid do you want? 
5
.****
.****
.****
.****
.****