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# Find Weekday using Zeller's Algorithm

Zeller’s Algorithm is used to find the weekday from a given date. The formula to find weekday using Zeller’s Algorithm is here:

The formula is containing some variables; They are −

d − The day of the date.

m: It is the month code. From March to December it is 3 to 12, for January it is 13, and for February it is 14. When we consider January or February, then given year will be decreased by 1.

y − Last two digits of the year

c − first two digits of the year

w − The weekday. When it is 0, it is Saturday, when it is 6, it means Friday

## Input and Output

Input: The day, month and the year: 4, 1, 1997 Output: It was: Saturday

## Algorithm

zellersAlgorithm(day, month, year)

**Input:** The date of the day.

**Output: **Which day it was, (Sunday to Saturday).

Begin if month > 2, then mon := month else mon := 12 + month decrease year by 1 y := last two digit of the year c := first two digit of the year w := day + floor((13*(mon+1))/5) + y + floor(y/4) + floor(c/4) + 5*c w := w mod 7 return weekday[w] //weekday will hold days from Saturday to Friday End

## Example

#include<iostream> #include<cmath> using namespace std; string weekday[7] = {"Saturday","Sunday","Monday","Tuesday","Wednesday","Thursday","Friday"}; string zellersAlgorithm(int day, int month, int year) { int mon; if(month > 2) mon = month; //for march to december month code is same as month else { mon = (12+month); //for Jan and Feb, month code will be 13 and 14 year--; //decrease year for month Jan and Feb } int y = year % 100;//last two digit int c = year / 100; //first two digit int w = (day + floor((13*(mon+1))/5) + y + floor(y/4) + floor(c/4) + (5*c)); w = w % 7; return weekday[w]; } int main() { int day, month, year; cout << "Enter Day: "; cin >>day; cout << "Enter Month: "; cin >>month; cout << "Enter Year: "; cin >>year; cout << "It was: " <<zellersAlgorithm(day, month, year); }

## Output

Enter Day: 04 Enter Month: 01 Enter Year: 1997 It was: Saturday

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