Zeller's Congruence is an algorithm devised by Christian Zeller to calculate the day of the week for any date. The algorithm provides a simple and efficient way to determine the weekday for any date in the Gregorian calendar.
After calculation, we got h value equal to 4 which means March 1, 2023, is Thursday.
Output:
The formula for Zeller's Congruence is given by:
Where:
- h is the day of the week (0 = Saturday, 1 = Sunday, 2 = Monday, ..., 6 = Friday)
- q is the day of the month
- m is the month (3 = March, 4 = April, ..., 14 = February)
- K is the year of the century (i.e., year mod 100)
- J is the zero-based century (actually ⌊ year/100 ⌋)
The result h corresponds to the days of the week, where 0 is Saturday, 1 is Sunday, and so on.
Here's a breakdown of the formula:
- The term adjusts for the months (January and February are counted as months 13 and 14 of the previous year).
- takes care of the year part.
- deals with the century adjustment.
Example: Let's calculate the day of the week for March 1, 2023.
C program Implementation of Zeller's Congruence.
// C program to find day of the week for a Date // Zeller's Congruence #include <stdio.h> int zellersCongruence(int day, int month, int year) { if (month < 3) { month += 12; year--; } int K = year % 100; int J = year / 100; int h = (day + (13 * (month + 1)) / 5 + K + K / 4 + J / 4 - 2 * J) % 7; // Convert h to a more conventional form // (0 = Saturday, 1 = Sunday, ..., 6 = Friday) return h % 7; } int main() { int day = 1, month = 3, year = 2023; int dayOfWeek = zellersCongruence(day, month, year); char arr[7][10] = {"Saturday", "Sunday", "Monday", "Tuesday", "Wednesday", "Thursday", "Friday"}; printf("March 1, 2023 is a %s", arr[dayOfWeek]); return 0; }
March 1, 2023 is a Wednesday
In this C program, the zellersCongruence function calculates the day of the week using Zeller's Congruence, and the result is then displayed in a user-friendly format.
