Trouble with destructor

If I do not use the destructor, then everything works fine, but when I add it, the following error occurs:

Exception thrown at 0x00742BAF in Bitwise.exe: 0xC0000005: Access violation reading location 0xDDDDDDDD.

Can anyone tell me what is happening and how I might be able to fix this problem?

Here is the code that is causing the problem:

typedef double *arr;

class twod {
  arr *ar;
  int row;
  int collum;

public:
  twod() {
    row = 3;
    collum = 3;
    ar = new arr[row];
    for (int i = 0; i < row; i++) {
      ar[i] = new double[collum];
    }
  }

  void setel() {
    for (int i = 0; i < row; i++) {
      for (int j = 0; j < collum; j++) {
        cin >> ar[i][j];
      }
    }
  }

  twod(int a, int b) {
    row = a;
    collum = b;
    ar = new arr[row];

    for (int i = 0; i < row; i++) {
      ar[i] = new double[collum];
    }
  }

  twod operator=(const twod &a) {
    if (this != &a) {
      for (int i = 0; i < row; i++) {
        delete[] ar[i];
      }
      delete[] ar;

      row = a.row;
      collum = a.collum;
      ar = new arr[row];

      for (int i = 0; i < row; i++) {
        ar[i] = new double[collum];
      }

      for (int i = 0; i < row; i++) {
        for (int j = 0; j < collum; j++) {
          ar[i][j] = a.ar[i][j];
        }
      }
    }

    return *this;
  }

  void out() {
    for (int i = 0; i < row; i++) {
      for (int j = 0; j < collum; j++) {
        cout << this->ar[i][j];
      }
      cout << endl;
    }
  }

  friend twod operator+(const twod &a, const twod &b);

  ~twod() {
    for (int i = 0; i < this->row; i++) {
      delete[] this->ar[i];
    }

    delete[] this->ar;
  }
};

twod operator+(const twod &a, const twod &b) {
  if (a.collum != b.collum || a.row != b.row) {
    cout << "cant" << endl;
    exit(0);
  } else {
    twod d(a.row, a.collum);
    for (int i = 0; i < d.row; i++) {
      for (int j = 0; j < d.collum; j++) {
        d.ar[i][j] = a.ar[i][j] + b.ar[i][j];
      }
    }
    return d;
  }
}

int main() {
  twod a(3, 3), b(3, 3), c;
  a.setel();
  a.out();
  b.setel();
  b.out();
  c = (a + b);
  c.out();
}