C++ Overloading Assignment - Exercise

Overloading the assignment operator

The matrix class

class matrix {
public:
   matrix(int d);
   matrix(int d1, int d2);
   ~matrix();
   int ub1() const { return (s1 - 1); }
   int ub2() const { return (s2 - 1); }
private:
   int**   p;
   int     s1, s2;
};

matrix::matrix(int d): s1(d), s2(d)
{
   if (d < 1) {
      cerr << "illegal matrix size"
        << d << "by" << d << "\n";
      exit(1);
   }
   p = new int*[s1];
   for (int i = 0; i < s1; i++)
      p[i] = new int[s2];
}

matrix::matrix(int d1, int d2): s1(d1), s2(d2) {
  if (d1 < 1 || d2 < 1) { 
    cerr << "illegal matrix size" << d1 << "by" << d2 << "\n"; 
    exit(1); 
  } 
  p = new int*[s1]; 
  for (int i = 0; i < s1; i++) 
    p[i] = new int[s2]; 
} 
matrix::~matrix(){ 
  for (int i = 0; i <= ub1(); ++i) 
   delete p[i]; delete []p;
}