/// <summary>
/// This method can be used to calculate the Easter Sunday date using one of three methods defined by
/// <see cref="EasterMethod"/>.
/// </summary>
/// <remarks>See the <see cref="EasterMethod"/> enumerated type for the ways in which Easter Sunday can
/// be calculated. A number of days can be added to or subtracted from the returned date to find other
/// Easter related dates (i.e. subtract two from the returned date to get the date on which Good Friday
/// falls).</remarks>
/// <param name="year">The year in which to calculate Easter</param>
/// <param name="method">The method to use for calculating Easter</param>
/// <returns>The date on which Easter falls in the specified year as calculated using the specified
/// method.</returns>
/// <exception cref="ArgumentOutOfRangeException">An exception is thrown if the year is not between 1583
/// and 4099 for the Orthodox and Gregorian methods or if the year is less than 326 for the Julian
/// method.</exception>
/// <example>
/// <code language="cs">
/// // Returns 04/11/2004 for Easter
/// dtEaster = DateUtils.EasterSunday(2004, EasterMethod.Gregorian);
///
/// // Calculate Good Friday from that date
/// dtGoodFriday = dtEaster.AddDays(-2);
/// </code>
/// <code language="vbnet">
/// ' Returns 04/11/2004 for Easter
/// dtEaster = DateUtils.EasterSunday(2004, EasterMethod.Gregorian)
///
/// ' Calculate Good Friday from that date
/// dtGoodFriday = dtEaster.AddDays(-2)
/// </code>
/// </example>
public static DateTime EasterSunday(int year, EasterMethod method)
{
int century, yearRem, temp, pfm, tabc, day, month;
// Validate year
if (method == EasterMethod.Julian && year < 326)
{
throw new ArgumentOutOfRangeException("year", year, LR.GetString("ExDUBadJulianYear"));
}
if (method != EasterMethod.Julian && (year < 1583 || year > 4099))
{
throw new ArgumentOutOfRangeException("year", year, LR.GetString("ExDUBadOrthGregYear"));
}
century = year / 100; // Get century
yearRem = year % 19; // Get remainder of year / 19
if (method != EasterMethod.Gregorian)
{
// Calculate PFM date (Julian and Orthodox)
pfm = ((225 - 11 * yearRem) % 30) + 21;
// Find the next Sunday
temp = year % 100;
day = pfm + ((20 - ((pfm - 19) % 7) - ((40 - century) % 7) - ((temp + (temp / 4)) % 7)) % 7) + 1;
// Convert Julian to Gregorian date for Orthodox method
if (method == EasterMethod.Orthodox)
{
// Ten days were skipped in the Gregorian calendar from October 5-14, 1582
day += 10;
// Only one in every four century years are leap years in the Gregorian calendar. Every
// century is a leap year in the Julian calendar.
if (year > 1600)
{
day += (century - 16 - ((century - 16) / 4));
}
}
}
else
{
// Calculate PFM date (Gregorian)
temp = ((century - 15) / 2) + 202 - (11 * yearRem);
switch (century)
{
case 21:
case 24:
case 25:
case 27:
case 28:
case 29:
case 30:
case 31:
case 32:
case 34:
case 35:
case 38:
temp--;
break;
case 33:
case 36:
case 37:
case 39:
case 40:
temp -= 2;
break;
default:
break;
}
temp %= 30;
pfm = temp + 21;
if (temp == 29 || (temp == 28 && yearRem > 10))
{
pfm--;
}
// Find the next Sunday
tabc = (40 - century) % 4;
if (tabc == 3)
{
tabc++;
}
if (tabc > 1)
{
tabc++;
}
temp = year % 100;
day = pfm + ((20 - ((pfm - 19) % 7) - tabc - ((temp + (temp / 4)) % 7)) % 7) + 1;
}
// Return the date
if (day > 61)
{
day -= 61;
month = 5; // Can occur in May for EasterMethod.Orthodox
}
else
if (day > 31)
{
day -= 31;
month = 4;
}
else
{
month = 3;
}
return(new DateTime(year, month, day));
}
/// <summary>
/// This method can be used to calculate the Easter Sunday date using one of three methods defined by
/// <see cref="EasterMethod"/>.
/// </summary>
/// <remarks>See the <see cref="EasterMethod"/> enumerated type for the ways in which Easter Sunday can
/// be calculated. A number of days can be added to or subtracted from the returned date to find other
/// Easter related dates (i.e. subtract two from the returned date to get the date on which Good Friday
/// falls).</remarks>
/// <param name="year">The year in which to calculate Easter</param>
/// <param name="method">The method to use for calculating Easter</param>
/// <returns>The date on which Easter falls in the specified year as calculated using the specified
/// method.</returns>
/// <exception cref="ArgumentOutOfRangeException">An exception is thrown if the year is not between 1583
/// and 4099 for the Orthodox and Gregorian methods or if the year is less than 326 for the Julian
/// method.</exception>
/// <example>
/// <code language="cs">
/// // Returns 04/11/2004 for Easter
/// dtEaster = DateUtils.EasterSunday(2004, EasterMethod.Gregorian);
///
/// // Calculate Good Friday from that date
/// dtGoodFriday = dtEaster.AddDays(-2);
/// </code>
/// <code language="vbnet">
/// ' Returns 04/11/2004 for Easter
/// dtEaster = DateUtils.EasterSunday(2004, EasterMethod.Gregorian)
///
/// ' Calculate Good Friday from that date
/// dtGoodFriday = dtEaster.AddDays(-2)
/// </code>
/// </example>
public static DateTime EasterSunday(int year, EasterMethod method)
{
int century, yearRem, temp, pfm, tabc, day, month;
// Validate year
if(method == EasterMethod.Julian && year < 326)
throw new ArgumentOutOfRangeException("year", year, LR.GetString("ExDUBadJulianYear"));
if(method != EasterMethod.Julian && (year < 1583 || year > 4099))
throw new ArgumentOutOfRangeException("year", year, LR.GetString("ExDUBadOrthGregYear"));
century = year / 100; // Get century
yearRem = year % 19; // Get remainder of year / 19
if(method != EasterMethod.Gregorian)
{
// Calculate PFM date (Julian and Orthodox)
pfm = ((225 - 11 * yearRem) % 30) + 21;
// Find the next Sunday
temp = year % 100;
day = pfm + ((20 - ((pfm - 19) % 7) - ((40 - century) % 7) - ((temp + (temp / 4)) % 7)) % 7) + 1;
// Convert Julian to Gregorian date for Orthodox method
if(method == EasterMethod.Orthodox)
{
// Ten days were skipped in the Gregorian calendar from October 5-14, 1582
day += 10;
// Only one in every four century years are leap years in the Gregorian calendar. Every
// century is a leap year in the Julian calendar.
if(year > 1600)
day += (century - 16 - ((century - 16) / 4));
}
}
else
{
// Calculate PFM date (Gregorian)
temp = ((century - 15) / 2) + 202 - (11 * yearRem);
switch(century)
{
case 21:
case 24:
case 25:
case 27:
case 28:
case 29:
case 30:
case 31:
case 32:
case 34:
case 35:
case 38:
temp--;
break;
case 33:
case 36:
case 37:
case 39:
case 40:
temp -= 2;
break;
default:
break;
}
temp %= 30;
pfm = temp + 21;
if(temp == 29 || (temp == 28 && yearRem > 10))
pfm--;
// Find the next Sunday
tabc = (40 - century) % 4;
if(tabc == 3)
tabc++;
if(tabc > 1)
tabc++;
temp = year % 100;
day = pfm + ((20 - ((pfm - 19) % 7) - tabc - ((temp + (temp / 4)) % 7)) % 7) + 1;
}
// Return the date
if(day > 61)
{
day -= 61;
month = 5; // Can occur in May for EasterMethod.Orthodox
}
else
if(day > 31)
{
day -= 31;
month = 4;
}
else
month = 3;
return new DateTime(year, month, day);
}
/// <summary>
/// Load the data grid with all Easter Sunday dates for the specified range of years
/// </summary>
/// <param name="sender">The sender of the event</param>
/// <param name="e">The event arguments</param>
private void btnEaster_Click(object sender, EventArgs e)
{
int fromYear, toYear, year;
string desc;
EasterMethod em = EasterMethod.Gregorian;
fromYear = (int)udcFromYear.Value;
toYear = (int)udcToYear.Value;
if (rbJulian.Checked)
{
em = EasterMethod.Julian;
}
else
if (rbOrthodox.Checked)
{
em = EasterMethod.Orthodox;
}
// Adjust years as necessary based on the method
if (em != EasterMethod.Julian)
{
if (fromYear < 1583)
{
fromYear = 1583;
}
if (fromYear > 4099)
{
fromYear = 4099;
}
if (toYear < 1583)
{
toYear = 1583;
}
if (toYear > 4099)
{
toYear = 4099;
}
}
else
{
if (fromYear < 326)
{
fromYear = 326;
}
if (toYear < 326)
{
toYear = 326;
}
}
if (fromYear > toYear)
{
year = fromYear;
fromYear = toYear;
toYear = year;
}
udcFromYear.Value = fromYear;
udcToYear.Value = toYear;
this.Cursor = Cursors.WaitCursor;
// Create the grid view's data source
List <ListItem> items = new List <ListItem>();
desc = String.Format("Easter ({0})", em.ToString());
while (fromYear <= toYear)
{
items.Add(new ListItem(DateUtils.EasterSunday(fromYear++, em), desc));
}
dgvDatesFound.DataSource = items;
this.Cursor = Cursors.Default;
}