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how to set up my for loop to print my array in reverse

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SyLk

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how to set up my for loop to print my array in reverse

Mar 10th, 2005

im having problems figuring out how to print this array in reverse.I believe it might be a logical issue. I don't want the answer. I'm thinkin my row must be initialized to the matrix.length. can someone give me a few hints as to go about this.

public static void printMatrixReverse(int [][]matrix)
{
int row, col;
for (row = 0 row < matrix.length;row++)
{
for (col=0;col < matrix[row].length;col++)
System.out.print(matrix[row][col] + "\t");
System.out.println();
}
}

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Narue

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Re: how to set up my for loop to print my array in reverse

Mar 10th, 2005

Start at array.length - 1 instead of 0, and make sure that you don't actually access the -1th index.

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Re: how to set up my for loop to print my array in reverse

Mar 10th, 2005

Hi everyone,

•

Originally Posted by SyLk

I don't want the answer

Do you want the question instead :mrgreen:

Just kidding

Is this what you want

 Help with Code Tags 
 Java Syntax (Toggle Plain Text) 
 
public static void printMatrixReverse(int [][]matrix)
{
	int row, col;
 
             for (row = matrix.length; row >= 0 ; row--)
	{
 
             for (col = matrix[row].length; col >= 0; col--)
	{
 
	System.out.print(matrix[row][col] + "\t");
	System.out.println();
 
	}
}
public static void printMatrixReverse(int [][]matrix)
{
	int row, col;
	
             for (row = matrix.length; row >= 0 ; row--)
	{
             
             for (col = matrix[row].length; col >= 0; col--)
	{

	System.out.print(matrix[row][col] + "\t");
	System.out.println();

	}
}

Let me know if it works

Yours Sincerely

Richard West

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SyLk

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Re: how to set up my for loop to print my array in reverse

Mar 10th, 2005

freesoft thats far from correct.

Narue can u explain to me why i would initialize row to matrix.length-1?

1 2 3
4 5 6
would'nt that cause my numbers to start at 5 instead of 6?

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Re: how to set up my for loop to print my array in reverse

Mar 10th, 2005

Here's a way of doing it, works best if you sort the array first, but you don't have to.

 Help with Code Tags 
 Java Syntax (Toggle Plain Text) 
import java.util.*;
 
class DescendingOrder 
{
  public static void main(String[] arguments) 
  {
           String[] names = {"a", "c", "f", "d", "e"};
           Arrays.sort(names);
 
          System.out.println("Descending order:");
 
              for (int a = 0; a < names.length; a++)
              {
                        System.out.println(a + names[names.length
                                        - 1 - a]);
              }
    }
}
import java.util.*;

class DescendingOrder 
{
  public static void main(String[] arguments) 
  {
           String[] names = {"a", "c", "f", "d", "e"};
           Arrays.sort(names);
  
          System.out.println("Descending order:");
        
              for (int a = 0; a < names.length; a++)
              {
                        System.out.println(a + names[names.length
                                        - 1 - a]);
              }
    }
}

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Re: how to set up my for loop to print my array in reverse

Mar 10th, 2005

Narue I got it done through a little bit of tial and error
but the concept of setting row = to matrix.length-1 is still puzzling
if u could clear this up for me i'd be very thankful.....TY

for (row=matrix.length-1;row>=0;row--)
{
for (col=matrix[row].length-1;col>=0;col--)
System.out.print(matrix[row][col] + "\t");
System.out.println();
}

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Re: how to set up my for loop to print my array in reverse

Mar 10th, 2005

•

Originally Posted by SyLk

Narue I got it done through a little bit of tial and error
but the concept of setting row = to matrix.length-1 is still puzzling
if u could clear this up for me i'd be very thankful.....TY

for (row=matrix.length-1;row>=0;row--)
{
for (col=matrix[row].length-1;col>=0;col--)
System.out.print(matrix[row][col] + "\t");
System.out.println();
}

I just gave you a clear example?

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Re: how to set up my for loop to print my array in reverse

Mar 10th, 2005

>Let me know if it works
If you tested it then you would find out that it accesses your arrays out of bounds.

>Narue can u explain to me why i would initialize row to matrix.length-1?
Arrays in Java are zero based, which means that the indices go from 0 to length-1. If you initialize the index variable to matrix.length then you'll be accessing the array out of bounds and it will throw an exception. Consider this array:

 Help with Code Tags 
 Java Syntax (Toggle Plain Text) 
int[] a = {7,3,5,8,1};
int[] a = {7,3,5,8,1};

The first item is 7 at a[0]. The fifth item is 1 at a[4]. a.length evaluates to 5, so what happens when you do this?

 Help with Code Tags 
 Java Syntax (Toggle Plain Text) 
public class ja {
  public static void main(String[] args)
  {
    int[] a = {7,3,5,8,1};
    System.out.println(a[5]);
  }
}
public class ja {
  public static void main(String[] args)
  {
    int[] a = {7,3,5,8,1};
    System.out.println(a[5]);
  }
}

Now what happens when you do the same thing in a different way?

 Help with Code Tags 
 Java Syntax (Toggle Plain Text) 
public class ja {
  public static void main(String[] args)
  {
    int[] a = {7,3,5,8,1};
    System.out.println(a[a.length]);
  }
}
public class ja {
  public static void main(String[] args)
  {
    int[] a = {7,3,5,8,1};
    System.out.println(a[a.length]);
  }
}

Now, just for grins, try this and see how it gives you the last item in the array:

 Help with Code Tags 
 Java Syntax (Toggle Plain Text) 
public class ja {
  public static void main(String[] args)
  {
    int[] a = {7,3,5,8,1};
    System.out.println(a[a.length - 1]);
  }
}
public class ja {
  public static void main(String[] args)
  {
    int[] a = {7,3,5,8,1};
    System.out.println(a[a.length - 1]);
  }
}

That's why I used matrix.length-1.

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Re: how to set up my for loop to print my array in reverse

Mar 10th, 2005

Mines better than yours :cheesy:

joking!

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Re: how to set up my for loop to print my array in reverse

#10

Mar 11th, 2005

Hi everyone,

I FORGOT THE -1 SO SUE ME

For the love of god any programmer would know that was a careless mistake.

Seriously sylk don't tell me you didn't realize that?

Richard West