Matrix Class

[NitaB]

I see this topic has been hacked to death but it seems to be slightly different in each case. Anyway, I've been chopping away at this code for awhile. I realize that it is easier to overload the () rather than the [] which is what I was determined to do at first. Anyway, so now that I've switched to (), my program can compile BUT I'm getting weirdo numbers. And now that I have no compiler errors to go over, I'm not sure where to start debugging.
Also, I don't quite understand how my operator() functions are working but I know they are necessary to overload () instead of [].
(Note: ignore the overloading functions. I'm sure I can get those to work once I've gotten my matrix to display correctly)
Any clarification and help is greatly appreciated!

This is my header file:

#include <iostream>
#include <limits.h>
using namespace std;

class Matrix
    {
    friend ostream& operator<<(ostream& out, const Matrix& m);
    friend Matrix operator-(const Matrix& m1, const Matrix & m2);
    friend Matrix operator*(const Matrix& m1, const Matrix & m2);
    friend Matrix operator++(const Matrix& m1);
    friend Matrix operator--(const Matrix& m1);
    friend void setMatrix(Matrix&, int);
    
public:                        
    Matrix(unsigned int r, unsigned int c);
    int& operator() (unsigned row, unsigned col);
    int  operator() (unsigned row, unsigned col) const;
    ~Matrix();
    //int getrows() const;
    //int getcols() const;
      
    Matrix operator+(const Matrix & m2);
private: 
     int rows;
     int cols;
     unsigned rows_;
     unsigned cols_;
     int *info;
};

This is my implementation file:

#include "Matrix.h"
#include <iostream>
using namespace std;


int rows, cols;
ostream& operator<<(ostream& out, const Matrix& m) 
{
    for(int i=0; i<m.rows; i++)
    {
     for(int j=0; j<m.cols; j++)
     {
             out<<m.info[i*m.cols+j];
     }
     out<<endl;
    }
    return out;
}

Matrix operator-(const Matrix& m1, const Matrix& m2) 
{
    rows=m1.rows-m2.rows;
    cols=m1.cols-m2.cols;
    return Matrix(rows, cols);
}

Matrix operator*(const Matrix& m1, const Matrix& m2) 
{
    rows=m1.rows*m2.rows;
    cols=m1.cols*m2.cols;
    return Matrix(rows, cols);
}

Matrix::Matrix(unsigned int r, unsigned int c)
           :rows(r), cols(c)
           {
                     info=new int[r*c];
           }

Matrix::~Matrix()
      {
             delete[] info;
      }
      
int& Matrix::operator() (unsigned row, unsigned col)
 {
   if (row >= rows_ || col >= cols_)
   return info[cols_*row + col];
 }
  
int Matrix::operator() (unsigned row, unsigned col) const
 {
   if (row >= rows_ || col >= cols_)
   return info[cols_*row + col];
 }  

      
//int Matrix::getrows() const
  //    {
    //      return rows;
      //}
      
//int Matrix::getcols() const
  //    {
    //      return cols;
      //}

And this is my very simple driver for now:

#include "Matrix.h"
#include <iostream>
#include <limits.h>
using namespace std;

int main() 
{

    Matrix M(4,3);
    
    M(0,0) = 25; M(0,1) = 7; M(0,2) = 42;
    M(1,0) = 38; M(1,1) = 85; M(1,2) = 21;
    M(2,0) = 14; M(2,1) = 65; M(2,2) = 92;
    M(3,0) = 47; M(3,1) = 55; M(3,2) = 10;
    
    cout<<M<<endl;

    
    system("pause");
    return 0;
}

[mrnutty]

>>info[cols_*row + col];
I don't think this conversion is right. Assuming you are using a 1D array.
Then our 1D array indices is like so :

0 1 2
3 4 5
6 7 8
9 10 11

Your conversion equation is " row*col+col ". Say we call matrix(1,1);
That should return the value stored at 4 right? But your equation says
that row*col + col == 1*1+1 = 2. which is not 4, as you need it to be.

A correct conversion function would be :

int& Matrix::operator() (unsigned row, unsigned col)
 {
   if (row < rows_ && col < cols_)
      return info[rows_ * row + col];
  else return -1;
 }

In the above code rows_ should be a const number of rows that the
matrix has. Also notice how the if statement changed. If the rows and columns index are less that the max number of rows and columns then
we return some value.

[NitaB]

Hi firstPerson!

Thanks for the suggestion. I understand the if statement but I don't understand why I have what I have in the return statement (info[rows_ * row + col]. Also, I get a compiler error saying invalid initialization of non-const reference of type int& from a temporary of type int. This error points to the "else return -1".

[NitaB]

Quick Note: I tried changing that one line around and got it to compile. However, when I ran the program a series of numbers ran down my screen and then the program terminated. -_-

[mrnutty]

>> out<<m.info[i*m.cols+j];

Change to :

out<<m.info[m.rows * i + j];

[NitaB]

Hmm, I did that. But I still get the same problem. I'll attach the files so you can see exactly what happens. (it's not pretty. lol)

I'm guessing the conversion is the problem...but I don't understand it. And I've read several tutorials but they use vectors and other things that I haven't learned yet.:S

>> out<<m.info[i*m.cols+j];

Change to :

out<<m.info[m.rows * i + j];