День недели по дате - C++ - Ответ 9545324

/* ******************************************************************** **
** @@ WeekDay()
** @  Copyrt : [url]http://mathforum.org/dr.math/faq/faq.calendar.html[/url]
** @  Author : Zeller's Rule
** @  Modify :
** @  Update :
** @  Notes  : WeekDay() computes the Day of the Week based upon the given Date,
** @  Notes  : Month and Year. It uses the Zeller Congruence Algorithim.
** @  Notes  : ([url]https://en.wikipedia.org/wiki/Zeller's_congruence[/url])
** @  Notes  : iDate  is the Day of the Month,   1 - 31
** @  Notes  : iMonth is the Month of the Year,  1 - 12
** @  Notes  : iYear  is the Year, e.g.,         2000
** @  Notes  : It returns 0 for SunDay, 1 for MonDay, etc.
** ******************************************************************** */
 
int WeekDay(int iYear,int iMonth,int iDay)
{
   // Month:  March   -  3 ... December - 12 of Current  Year
   //         January - 13,    February - 14 of Previous Year
   if (iMonth < 3) 
   { 
      // If January or February, adjust Month and Year
      iMonth += 12;
      --iYear;
   }
 
   int   N1 = (26 * (iMonth + 1)) / 10;    // Month Shift
   int   N2 = (125 * iYear) / 100;         // Leap Correction
 
   int   N3 = iDay + N1 + N2 - (iYear / 100) + (iYear / 400) - 1;
 
   return N3 % 7;
}