/* Code for exercise 7.19. |  | "C++ Solutions--Companion to The C++ Programming Language, Third Edition" | by David Vandevoorde; Addison-Wesley 1998; ISBN 0-201-30965-3. | | Permission to use, copy, modify, distribute and sell this software | and its documentation for any purpose is hereby granted without fee. | The author makes no representations about the suitability of this | software for any purpose.  It is provided "as is" without express or | implied warranty. `----------------------------------------------------------------------*//* Notes:This program borrow from Ch5/ex5_13.cpp.*/#include <iostream>#include <stdlib.h>struct Date {   unsigned day_: 5; // Bitfield: use only 5 bits to                    //  represent this integer member   unsigned month_: 4;   int year_: 15;};bool is_leapyear(int y) {   return !(y%4) and ((y%100) or !(y%400));} // y is a multiple of 4, but not a multiple of 100  // that is not a multiple of 400.struct Month {   enum { Jan = 1, Feb, Mar, Apr, May, Jun,          Jul, Aug, Sep, Oct, Nov, Dec };   static int n_days(int m, int y) {      return m!=Feb? n_days_[m-1]                   : (is_leapyear(y)? 29: 28);   }private:   static int const n_days_[12];};int const Month::n_days_[12]   = { 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31 };std::istream& operator>>(std::istream &input, Date &d) {   int const bufsize = 6;   char buffer[bufsize];   input.getline(buffer, bufsize, '/');   d.month_ = atoi(buffer);   input.getline(buffer, bufsize, '/');   d.day_ = atoi(buffer);   int y;   input >> y;   d.year_ = y;    return input;}std::ostream& operator<<(std::ostream &output, Date const &d) {   output << d.month_ << '/' << d.day_ << '/' << d.year_;   return output;}Date& init(Date &d, unsigned day, unsigned month, int year) {   d.day_ = day;   d.month_ = month;   d.year_ = year;   return d;}Date next_year(Date const &d) {   Date n;   n.day_ = d.day_;   n.month_ = d.month_;   n.year_ = d.year_+1;   // February 29, but not a leap year?   if (n.day_>Month::n_days(n.month_, n.year_)) {      n.day_ = 1; n.month_ = 3;   }   return n;}Date next_month(Date const &d) {   Date n;   n.day_ = d.day_;   n.month_ = d.month_%12+1;   n.year_ = d.year_;   if (n.month_==1)      n = next_year(n);   if (n.day_>Month::n_days(n.month_, n.year_))      n.day_ = Month::n_days(n.month_, n.year_);   return n;}Date next_day(Date const &d) {   Date n;   n.day_ = (d.day_)%Month::n_days(d.month_, d.year_)+1;   n.month_ = d.month_;   n.year_ = d.year_;   if (n.day_==1)      return next_month(n);   else      return n;}int MS[] = { 0, 3, 3, 6, 1, 4, 6, 2, 5, 0, 3, 5 };enum DayOfWeek { Sunday = 0, Monday, Tuesday, Wednesday,                 Thursday, Friday, Saturday };DayOfWeek day_of_week(Date const &dt) {   int const y = dt.year_, m = dt.month_, d = dt.day_;   int const j1 = (1+y-1+(y-1)/4-(y-1)/100+(y-1)/400)%7;   if (m<=2 or !is_leapyear(y))      return DayOfWeek((j1+MS[m-1]+d-1)%7);   else      return DayOfWeek((j1+MS[m-1]+d)%7);}Date next_Monday(Date const &d) {   DayOfWeek dday = day_of_week(d);   int const n_days = (dday==Sunday)? 1: 8-dday;   Date Monday(d);   for (int k = 0; k!=n_days; ++k)      Monday = next_day(Monday);   return Monday;}char const *month_name[7] = { "Sunday", "Monday", "Tuesday", "Wednesday",                              "Thursday", "Friday", "Saturday" };int main() {   Date input;   std::cout << "Input Date (M/D/Y, e.g. 7/21/1969): ";   std::cin >> input;   std::cout << "Cannonical output: " << input << '\n';   std::cout << "This is a " << month_name[day_of_week(input)] << '\n';   std::cout << "The next day is " << next_day(input) << '\n';   std::cout << "The next Monday is " << next_Monday(input) << '\n';   std::cout << "In one month is will be " << next_month(input) << '\n';   std::cout << "One year from " << input             << " will be " << next_year(input) << '\n';   return 0;}