program keeps crashing

[sexyzebra19]

My program keeps crashing and I can't see why...pretty sure its something to do with creating matrix B since when I remove the commands to create matrix B it runs ok. Can anyone see what is wrong?

Thanks in advance!

I have the header file:

// matrixlib.h - A header file for a simple matrix library
#include<string>
#include<vector>

class Matrix {
 public:

  Matrix(int mdim, int ndim);
  // Create a zero matrix with mdim rows and ndim columns

  Matrix(int ndim);
  // Create an zero ndim x ndim matrix

  void Add(Matrix b);
  // Add Matrix b to this matrix

  void SetElement(int m, int n, double d);
  // Set Element at position (m,n) to the value d

 private:
  int mdim_; // Number of rows of matrix
  int ndim_; // Number of columns of matrix
  std::vector<double> data_; // Vector storing the matrix data
};

and main:

#include<iostream>
#include<vector>
#include<cmath>
#include "matrixlib.h"

using namespace std;

int main()
{
   // Create a new instance of Matrix named A with 2 rows and 3 columns
    Matrix A(2);
    Matrix B(2);

    A.SetElement(1,1,1);
    A.SetElement(1,2,2);
    A.SetElement(2,1,3);
    A.SetElement(2,2,4);

    B.SetElement(1,1,5);
    B.SetElement(1,2,6);
    B.SetElement(2,1,7);
    B.SetElement(2,2,8);

    A.Add(B);

    return 0;
}

Matrix::Matrix(int mdim_, int ndim_)
{
    data_.resize (mdim_*ndim_);

    for (int i = 0; i < mdim_*ndim_; i++)
    {
		data_[i] = 0;
	}
}

Matrix::Matrix(int ndim_)
{
    data_.resize (ndim_*ndim_);

    for (int i = 0; i < ndim_*ndim_; i++)
    {
		data_[i] = 0;
	}
}

void Matrix::Add(Matrix b)
{
        for (int i = 0; i < data_.size(); i++)
        {
            data_[i] += b.data_[i];
            cout<<" "<<data_[i]<<" ";
        }
}
// Add Matrix b to this matrix

void Matrix::SetElement(int m, int n, double d)
{
    data_[((n*ndim_)-1)-(ndim_- m)] = d;
}
// Set Element at position (m,n) to the value d

[Ancient Dragon]

The main problem with that class is that the constructor with only one constructor does not initialize the value of both class member variables mdim_ and ndim_.

[sexyzebra19]

Thanks for the reply Ancient Dragon, I am not able to change anything in the header file, so is there a way to initalize these variables within the .cpp file?

I tried setting them to 0 within the Matrix:: functions but no luck...

[mitrmkar]

I am not able to change anything in the header file, so is there a way to initalize these variables within the .cpp file?

Yes, there is. For example,

Matrix::Matrix(int mdim_, int ndim_)
{
  this->mdim_ = mdim_;
  this->ndim_ = ndim_;

You could/should also change to ..

Matrix::Matrix(int [I]rows[/I], int [I]cols[/I])
{
  mdim_ = rows;
  ndim_ = cols;

That would be more clear, as it is quite confusing when the incoming arguments are named exactly as the member variables.

And furthermore, given a matrix class, sticking to variable names in terms of rows/columns would be more readable (i.e. instead of mdim_/ndim_ and also plain m and n elsewhere in the code).

Note that you have to fix both constructors so that the dimensions are stored properly upon construction.

[sexyzebra19]

Fantastically helpful as usual, its working fine now thanks mitrmkar.