Matrix class: unknown problems in C++ - c++

Question

My program compiles but has these problems:
It's not using the member function fill (now). When i got the fill function to work (a while ago), it didn't do adding, subtracting, and multiplication correctly because it didn't record the second matrix it was supposed to do those things with. I got it to work the way you see it now, but this is the result:
ubuntu:~/Desktop$ ./matrix
2
2
enter the matrix element by element(starting from the first row)
1
2
1
2
Segmentation fault (core dumped)
If someone can point out the mistakes, it would be greatly appreciated:
#include <iostream>
#include <cmath>
using namespace std;
class matrix
{
private:
int r;
int c;
double** arr;
double** arr2;
public:
matrix()
{
r = 1;
c = 1;
arr = 0;
arr2 = 0;
}
matrix(int rows, int columns)
{
r = row(r);
c = column(c);
arr = new double* [r];
for(int i =0; i<r; i++)
{
arr[i] = new double[c];
}
}
matrix(matrix& a)
{
r = a.row(r);
c = a.column(c);
arr = new double* [r];
for(int i =0; i<r; i++)
{
arr[i] = new double[c];
}
}
~matrix()
{
for( int i = 0 ; i < r ; i++ )
{
delete [] arr[i];
}
delete [] arr;
}
void copy()
{
arr2 = new double* [r];
for(int i =0; i<r; i++)
{
arr2[i] = new double[c];
}
for (int i=0; i<r; i++)
{
for(int j=0; j<c; j++)
{
arr2[i][j] = arr[i][j];
}
}
}
int row(int r)
{
return r;
}
int column(int c)
{
return c;
}
void fill(const int& r, const int& c)
{
for (int i=0; i<r; i++)
{
for(int j=0; j<c; j++)
{
cin>>arr[i][j];
}
}
}
void print()
{
for (int i=0; i < r; i++)
{
for (int j=0; j<c; j++)
{
cout<<arr[i][j]<<" ";
}
cout<<endl;
}
}
void sum()
{
double ** arr2 = arr;
cout << "enter the matrix you want to add" << endl;
fill(r, c);
for (int i=0; i<r; i++)
{
for(int j=0; j<c; j++)
{
arr[i][j] = (arr2[i][j] + arr[i][j]);
}
}
print();
}
void sub()
{
double ** arr2 = arr;
cout << "enter the matrix you want to subtract" << endl;
fill(r,c);
for (int i=0; i<r; i++)
{
for(int j=0; j<c; j++)
{
arr[i][j] = (arr2[i][j]) - (arr[i][j]);
}
}
print();
}
void multiplication()
{
double ** arr2 = arr;
cout << "enter the matrix you want to multiply by" << endl;
fill(r,c);
int k =0;
double ** arrm = arr;
for(int i=0;i< r;i++)
{
for(int j=0;j< c;j++)
{
arrm[i][j] = 0;
for(k=0;k< r;k++)
{
arrm[i][j] = arrm[i][j] + arr2[i][k] * arr[k][j];
}
}
}
print();
}
bool check(const int r, const int c)
{
if(r==c)
{return true;}
else
{return false;}
}
void get_det(const int r, const int c)
{
if(check(r,c) == true)
{
int n = r;
Determinant(arr,n);
cout <<"the determinant is: "<< endl;
}
else
{
cout << "can't" << endl;
}
}
double Determinant(double** arr, int n)
{
double det = 0;
double** m = NULL;
if (n == 1)
{ det = arr[0][0];}
else if (n == 2)
{
det = arr[0][0] * arr[1][1] - arr[1][0] * arr[0][1];
}
else if (n == 3)
{
det = arr[0][0]*(arr[1][1]*arr[2][2] - arr[1][2]*arr[2][1])
+ arr[0][1]*(arr[1][2]*arr[2][0] - arr[1][0]*arr[2][2])
+ arr[0][2]*(arr[1][0]*arr[2][1] - arr[1][1]*arr[2][0]);
}
else if (n > 3)
{
for (int j1=0;j1<n;j1++)
{
m = new double* [n-1];
for (int i=0;i<n-1;i++)
m[i] = new double[n-1];
for (int i=1;i<n;i++)
{
int j2 = 0;
for (int j=0;j<n;j++)
{
if (j == j1) continue;
m[i-1][j2] = arr[i][j];
j2++;
}
}
det += pow(-1,1+j1+1) * arr[0][j1] * Determinant(m,n-1);
for (int i=0;i<(n-1);i++)
delete m[i];
delete m;
}
}
return(det);
}
};
int main()
{
int r,c,answer;
cin >> r >> c;
matrix g(r,c);
cout << "enter the matrix element by element(starting from the first row)" << endl;
g.fill(r,c);
cout << "do you want add (1=yes / 0=no)" << endl;
cin >> answer;
if(answer == 1)
{
g.sum();
}
else{}
cout << "do you want subtract (1=yes / 0=no)" << endl;
cin >> answer;
if(answer == 1)
{
g.sub();
}
else{}
cout << "do you want multiply (1=yes / 0=no)" << endl;
cin >> answer;
if(answer == 1)
{
g.multiplication();
}
else{}
cout << "do you want to know the determinant (1=yes / 0=no)" << endl;
cin >> answer;
if(answer == 1)
{
g.get_det(r,c);
}
else{}
return 0;
}