Date& operator++(Date& d)
{
    //add 1 to d  //tomorrow, unless we were at the end of the month
    //if is_date is false
    //            //need to change to first of next month
    //  set d to 1
    //  if m is December
    //            //need to change to next year too
    //    set m to January
    //    increment y
    //  else
    //    increment m
    //return *this;
}