Assignment Operator

 List&  List::operator=(const  List  &o)  {
     if  (this  ==  &o)  return  *this;
     Node  *c  =  head;
     while  (c)  {
         Node  *r  =  c;
         c  =  c->next;  delete  r;
     }
     if  (o.head  ==  NULL)  head  =  NULL;
     else  {
         // insert rest of copy code
     }  return  *this;  }