class Matrix2 that stores two dimensional matrix

[sys7em]

Hello guys,

I'm a beginner in c++ and i stumbled upon a problem. I have to define a class Matrix2 that stores two dimensional matrix, by keeping its elements in a dynamically allocated array of integers (int **a;).

I have come up with this code. Is this correct?

class Matrix2{

 int **p2DArray;
 const int Rows = 50;
 const int Cols = 2;
public:

 // Constructor
 Matrix2() {
  // Allocate Memory
  p2DArray = new int*[Rows];
  for (int i = 0; i < Rows; ++i)
    p2DArray[i] = new int[Cols];
 }

 // De-Constructor
 Matrix2() {
  // De-Allocate so we don't have memory leak
  for (int i = 0; i < Rows; ++i)
   delete [] p2DArray[i];

  delete [] p2DArray;
 } 

 // Do Something
 void doSomething() {
  p2DArray[someRow][someCol] = 12;
 }
}

[Hammurabi]

You don't want Rows and Cols to be const since dynamic size is the whole point. Those sizes will need to be passed in to the constructor.

Matrix2( int rows, int cols )
  : Rows(rows), Cols(cols)
{
    // ...
}

Another way to allocate the memory is to allocate one chunk of integers like this:

// Declare
int* p2DArray;

// Allocate
p2DArray = new int*[ Rows * Cols ];

// Acccess
int n = p2DArray[someRow * Cols + someCol]

// Deallocate
delete[] p2DArray;

That's particularly good if you're allocating/deallocating a lot, since it's just one big chunk instead of a bunch of rows.

[sys7em]

thanks for your reply.

And how can I demonstrate with this class:

the difference between initialization

        Matrix2 s;
        Matrix2 t = s;

and assignment

     Matrix2 s;
        Matrix2 t;
        s = t;

?

[Hammurabi]

What do you have so far?

[sys7em]

I got nothing. That's why I'm asking what is the difference.