2D array battleship

[Haani Naz]

Hi,

been reading up head first java. there's a bit about creating a battleship game and i just jumped ahead and tried doing it myself.

so far i managed to create a grid which populates ships denoted by 'x' in 3 cells. i'm having trouble getting the checks right if it tries to populate it in the same cells.


here is my code. please assist in giving me advice is getting it to work, i'd really appreciate it.

import java.util.*;
import java.math.*;

public class Array2DTest {

	 public static void main(String[] args) {

	        //create the grid
	        final int rowWidth = 5;
	        final int colHeight = 5;
	        
	        
	        
	        Random rand = new Random();
	            
	        String [][] board = new String [rowWidth][colHeight];
	            
	        //fill the grid
	        
	        for (int row = 0; row < board.length; row++) {
	        	
	        	
	            for (int col = 0; col < board[row].length; col++) {
	              
	            	
	            	board[row][col] = "-";  //rand.nextInt(10);
	            }
	            
	          
	        }
	        
	        
	       // System.out.println("Board length: " + board[1].length);        
	        
	        
	        //to randomly decide if the ships are assigned to the grid via row or column
	        int toss;
	        
	       
	        
	        int row_pos;
	        int column_pos;
	        int count = 0; // run through the grid 3 times and create 3 ships
	       
	        
	        while (count < 3){
	        
	        	
	        	//i'm forcing it only use rows at this point. 
	        	 toss = 1;  //rand.nextInt(2)
	        	
	        
	        if (toss == 1){
	        	
	        	row_pos=rand.nextInt(5); //random row is assigned
	        	System.out.println("row position: " + row_pos);
	        	count++;
	        	
	        	
	        	
	        	int temp;
	        	int rowSpace;
	        	int i=0; 
	        	int col=0;
	        	
	        	//creating a ship. 3 'x' markers on the board. loop 3 times.
	        	while( i < 3){
	        		
	        		
	        		//if row already has a 'x'. move to next column
	        		while ( board[row_pos][col] == "x"){
	        			
	        			col++;
	        			System.out.println("col increment: " + col);
	        			
	        			
	        		        			
	        			
	        		}
	        		
	        		//System.out.println("board length marker 1: " + board[row_pos].length);
	        		
	        		
	        		
	        		if ((rowSpace=( 1 + board.length) - col) >= 3 )
	        		{
	        		
	        			System.out.println("board length marker 2: " + rowSpace );
	        			board[row_pos][col]= "x";
	        		    col++;
	        		    i++;
	        		}
	        		else
	        		{
	        			
	        			
	        			
	        			//if no more cells available in row, generate a new row position
	        			
	        			while ( (temp = rand.nextInt(5)) != row_pos)
	        			
	        			{
	        			   row_pos = temp;	
	        			}
	        			
	        			
	        			
	        		}
	        		
	        		
	        		
	        		
	        	}//end-i < 3
	       
	        	 
	        }
	        
	        
	       
	        
	      /*  else if (toss == 0)
	        {
	        	
	        	column_pos=rand.nextInt(5);
	        	System.out.println("column position: " + column_pos);
	        	count++;
	        	
	        	int i=0;
	        	int row=0;
	        	while( i < 3){
	        		
	        		board[row][column_pos]= "x";
	        		row++;
	        		i++;
	        	}
	        	
	        	
	        }*/
	        	
	      
	        }//end-count < 3

	        	
	        	
	        

	        System.out.println("Printing starts here..");
	        
	        //display output
	        for(int i = 0; i < board.length; i++) {
	        	
	        	
	            for(int j = 0; j < board[i].length; j++) {
	                
	            	
	                System.out.print(board[i][j] + " ");
	                //System.out.println();
	            }
	            System.out.println();
	        }

	    } //end of main
	
	
	
}

here's a working output for me:


row position: 2
board length marker 2: 6
board length marker 2: 5
board length marker 2: 4
row position: 0
board length marker 2: 6
board length marker 2: 5
board length marker 2: 4
row position: 4
board length marker 2: 6
board length marker 2: 5
board length marker 2: 4
Printing starts here..
x x x - -
- - - - -
x x x - -
- - - - -
x x x - -


non-working output:

row position: 2
board length marker 2: 6
board length marker 2: 5
board length marker 2: 4
row position: 1
board length marker 2: 6
board length marker 2: 5
board length marker 2: 4
row position: 1
col increment: 1
col increment: 2
col increment: 3
board length marker 2: 3



As you can see as soon as its the same row it fails to work. it also fails to print the grid : /

Thanks in advance.

[Stephan van Hulst]

The problem is that in your while loop, you check for three placed ships. i only gets increased if rowSpace >= 3, which will never happen if two ships are in the same row, because col gets incremented to 3, then once more to 4, and after that (5+1-col) will never be >= 3. So you're stuck in an infinite loop.

An important note about your code. NEVER use assignment expressions within another expression, like you do with rowSpace. Assign the value to rowSpace in the line before it, and then use rowSpace in the expression afterwards. When I saw the code I immediately thought your bug was there, because you had intended it to be an == instead of an =. So don't do it.