---------filename: doomsday.cpp ------------
#include <iostream.h>
#include <conio.h>

int doomsday(int month, int day, int year);
bool isLeapYear(int year);
int dayOfWeek(int year);

void main()
{
   int day, month, year, day_of_week;

   cout << "Please enter the month: ";
   cin >> month;
   cout << "\nPlease enter the day: ";
   cin >> day;
   cout << "\nPlease enter the year: ";
   cin >> year;

   day_of_week = doomsday(month,day,year);

   cout << endl << month << "/" << day << "/" << year << " is a ";
   switch (day_of_week)
   {
   	case 0:
      	cout << "Monday.";
         break;
      case 1:
      	cout << "Tuesday.";
         break;
      case 2:
      	cout << "Wednesday.";
         break;
      case 3:
      	cout << "Thursday.";
         break;
      case 4:
      	cout << "Friday.";
         break;
      case 5:
      	cout << "Saturday.";
         break;
      case 6:
      	cout << "Sunday.";
   }
	getch();
}

int doomsday(int month, int day, int year)
{

	bool leapYear = isLeapYear(year);
   bool oddMonth = month%2;
   int doomsdayDayOfWeek = dayOfWeek(year);
   int doomsdayOfMonth;

   if(oddMonth)
   {
      if(1 == month)
      {
      	if(leapYear)
         	doomsdayOfMonth = 32;
         else
         	doomsdayOfMonth = 31;
      }
   	else if(5 == month)
      	doomsdayOfMonth = 9;
      else if(7 == month)
      	doomsdayOfMonth = 11;
      else if(9 == month)
      	doomsdayOfMonth = 5;
      else
      	doomsdayOfMonth = 7;
   }

   else
   {
      if(2 == month)
      {
      	if(leapYear)
         	doomsdayOfMonth = 29;
         else
         	doomsdayOfMonth = 28;
      }
      else
   		doomsdayOfMonth = month;
   }

   int daysFromDoomsday;
   int offsetFromDoomsdayDayOfWeek;

   if(day < doomsdayOfMonth)
   {
   	daysFromDoomsday = doomsdayOfMonth - day;
      offsetFromDoomsdayDayOfWeek = daysFromDoomsday%7;
      if(offsetFromDoomsdayDayOfWeek > doomsdayDayOfWeek)
      	return (doomsdayDayOfWeek - offsetFromDoomsdayDayOfWeek)+7;
      else
      	return doomsdayDayOfWeek - offsetFromDoomsdayDayOfWeek;
   }
   else
   {
      daysFromDoomsday = day - doomsdayOfMonth;
      offsetFromDoomsdayDayOfWeek = daysFromDoomsday%7;
      return (doomsdayDayOfWeek + offsetFromDoomsdayDayOfWeek)%7;
   }
}

bool isLeapYear(int year)
{
	if (0 == year%400)
      return true;
   else if(0 == year%100 && 0 == year%4)
		return false;
   else if (0 == year%4)
   	return true;
   else
      return false;
}

int dayOfWeek(int year)
{
   int day = 0;
   int yearCounter = 1898;

	if(year < 1898)
   {

   	while(yearCounter!=year)
      {
      	if(isLeapYear(yearCounter))
         	day += 2;
         else
         	day++;
         yearCounter--;
      }
	return (7-(day%7));
   }
   else
   {
      while(yearCounter!=year)
      {
       	yearCounter++;
			if(isLeapYear(yearCounter))
         	day += 2;
         else
         	day++;

      }
   return day%7;
   }
}