Thread: 2D array problem

What the program is supposed to do:
Write a program which builds two dimensional array ( n x n matrix ) with the dimentions entered by the user, populates the array with random numbers from 0 to 9, builds 2 transpose matrixes (using both diagonals), and displays Them all.
For example,
Enter a matrix size: 4

Original:
4 5 2 0
7 2 1 4
9 4 2 0
7 8 9 3

Transpose 1:
4 7 9 7
5 2 4 8
2 1 2 9
0 4 0 3

Transpose 2:
3 0 4 0
9 2 1 2
8 4 2 5
7 9 7 4

My code so far:

import java.util.Scanner;
class Ex2DArray
  {
    static int i,j,n,k;
	static int a[][];
    public static void main (String[] args)
	  {
	    Scanner input = new Scanner(System.in);
		System.out.println("Enter the number of the matrix:");
		int n = input.nextInt();
		a = new int [n][n];
		for (i=0;i<n;i++){
		  for (j=0;j<n;j++){
		    a[i][j] = (int)(Math.random()*10);
		  }
	    }
		System.out.println("Original:");
		//printArray();
		 for (i=0;i<n;i++){
		  for (j=0;j<n;j++){
		    System.out.print(a[i][j]+" ");
		  }
		  System.out.println();
		}
		for (i=0;i<n;i++){
		  for (j=0;j<i;j++){
		    k = a[j][i];
			a[j][i] = a[i][j];
			a[i][j] = k;
		  }
		}
		System.out.println("Transpose 1:");
		//printArray();
		 for (i=0;i<n;i++){
		  for (j=0;j<n;j++){
		    System.out.print(a[i][j]+" ");
		  }
		  System.out.println();
		}
		for (i=0;i<n;i++){
		  for (j=1;j<n;j++){
		    k = a[n-j-1][n-i-1];
			a[n-j-1][n-i-1] = a[i][j];
			a[i][j] = k;
		  }
		}
		System.out.println("Transpose 2:");
		//printArray();
		 for (i=0;i<n;i++){
		  for (j=0;j<n;j++){
		    System.out.print(a[i][j]+" ");
		  }
		  System.out.println();
		}
	}
    public static void printArray()
	  {
	    for (i=0;i<n;i++){
		  for (j=0;j<n;j++){
		    System.out.print(a[i][j]+" ");
		  }
		  System.out.println();
		}
	}
}

The problem is that it does nothing for Transpose 2, it somehow copies the same values of Transpose 1. How do I fix this?

Output:
Enter the number of the matrix:
4
Original:
2 9 0 4
2 6 2 5
4 8 6 3
8 8 9 3
Transpose 1:
2 2 4 8
9 6 8 8
0 2 6 9
4 5 3 3
Transpose 2:
3 2 4 8
3 6 8 8
5 2 6 9
4 0 9 2
Press any key to continue . . .

The output should be like this:
Enter the number of the matrix:
4
Original:
2 9 0 4
2 6 2 5
4 8 6 3
8 8 9 3
Transpose 1:
2 2 4 8
9 6 8 8
0 2 6 9
4 5 3 3
Transpose 2:
3 3 5 4
9 6 2 0
8 8 6 9
8 4 2 2

Originally Posted by Norm

Can you explain what is wrong with the output?

A suggestion for testing. Make the changes you see here on three lines:

		int n = 4; // input.nextInt();
                int nbr = 0;           //  to generate contents
		a = new int [n][n];
		for (i=0;i<n;i++){
		  for (j=0;j<n;j++){
		    a[i][j] = nbr++; //(int)(Math.random()*10);  // sequential nbrs

You misunderstand me. Look at this original set of numbers:
4 5 2 0
7 2 1 4
9 4 2 0
7 8 9 3

Transpose 1:
2 2 4 8
9 6 8 8
0 2 6 9
4 5 3 3

You simply switch 2 and 9, 4 and 0, and so on..

Transpose 2 (Here is where I'm stuck at):
3 0 4 0
9 2 1 2
8 4 2 5
7 9 7 4

This time you switch 2 and 4, 5 and 0 and so on...

Originally Posted by Norm

Can you explain what is wrong with the output?

A suggestion for testing. Make the changes you see here on the three lines with comments:

		int n = 4; // input.nextInt();
                int nbr = 0;           //  to generate contents
		a = new int [n][n];
		for (i=0;i<n;i++){
		  for (j=0;j<n;j++){
		    a[i][j] = nbr++; //(int)(Math.random()*10);  // sequential nbrs

Can you tell me what "nbr" stand for?