struct Date {

  int day, month, year;

};

// reads a date (in dd mm yyyy format) from the specfied input stream.
// if an error of any sort (bad read, invalid date) occurs, the input
// stream is left in the failed state.
void readDate (Date &date, istream &is);

// writes a date to the specified output stream (in dd/mm/yyyy format)
void writeDate (const Date &date, ostream &os);

// moves a date the specified number of days forward (positive day
// values) or backwards (negative day values)
void moveDate (Date &date, int days);