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109 lines
3.4 KiB
C++
109 lines
3.4 KiB
C++
/*
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* @file
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* @brief Determines the date of Easter after 1582
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*
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* @details
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* The date of Easter is determined in each year through a calculation known as
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* "computus." Easter is celebrated on the first Sunday after the Paschal full
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* moon, which is the first full moon on or after 21 March. Determining this
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* date in advance requires a correlation between the lunar months and the solar
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* year, while also accounting for the month, date, and weekday of the Julian or
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* Gregorian calendar. The complexity of the algorithm arises because of the
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* desire to associate the date of Easter with the date of the Jewish feast of
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* Passover which, Christians believe, is when Jesus was crucified.
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*
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* You can read more about the date of Easter here:
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* https://en.wikipedia.org/wiki/Date_of_Easter
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*
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* @author [AlternateWalls](https://github.com/AlternateWalls)
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*/
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#include <cassert> /// for assert
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#include <iostream> /// for IO operations
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/*
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* @brief Contains information for Easter date
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*/
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class EasterYearMonthDay {
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public:
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int year; ///< year Easter is on
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int month; ///< month Easter is on
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int day; ///< day Easter is on
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EasterYearMonthDay(int newYear, int newMonth, int newDay) {
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year = newYear; // Assigns year to class
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month = newMonth;
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day = newDay;
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}
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};
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/*
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* @brief Function that finds the month and day of Easter
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* @params param1 An int "y" of the year you want to find Easter on after
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* 1582
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* @returns An instance of the easterYearMonthDay calss that contains the
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* information (Ex. 420 - 4/20 or April 20th)
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*/
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EasterYearMonthDay findEaster(int y) {
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if (y > 1582) {
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int a = y % 19; // Year's location on Metonic Calendar
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int b = y / 100; // Century index
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int c = y % 100;
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int d = b / 4;
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int e = b % 4; // Takes into account leap years
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int f = (b + 8) / 25;
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int g = (b - f + 1) / 3;
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int h = (19 * a + b - d - g + 15) %
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30; // Days from Mar. 21st until the full moon
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int i = c / 4;
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int k = c % 4;
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int r = (32 + 2 * e + 2 * i - h - k) %
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7; // The number of days from Paschal full moon to next Sunday
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int m = (a + 11 * h + 22 * r) / 451;
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int n = (h + r - 7 * m + 114) / 31; // Month of Easter
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int p = (h + r - 7 * m + 114) % 31; // p + 1 is the day of Easter
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// Assign values
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EasterYearMonthDay date(
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y, n, p + 1); // Assign values to new instance of class
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// Return date
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return date;
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} else {
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EasterYearMonthDay date(0, 0, 0);
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// Return date
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return date;
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}
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}
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static void test() {
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/*
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* @brief Inputting different year values and comparing the outputs to a
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* calendar
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*/
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// 2003 | April 20th
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assert(findEaster(2003).month == 4); // Should return true
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assert(findEaster(2003).day == 20); // Should return true
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// 1910 | March 27th
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assert(findEaster(1910).month == 3); // Should return true
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assert(findEaster(1910).day == 27); // Should return true
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// 1877 | April 1st
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assert(findEaster(1877).month != 3); // Should return true
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assert(findEaster(1877).day != 22); // Should return true
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// 1400 | Invalid date
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assert(findEaster(1400).month == 0); // Should return true
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assert(findEaster(1400).day == 0); // Should return true
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}
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// Main
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int main() {
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test();
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return 0;
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}
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