Fun feature: Easter and Leap year

[chlordk]

Looks great. Everything is almost here only easter is missing.

Easter can be a little tricky. Here is a simple example in C.

/* Source: https://www.rmg.co.uk/stories/topics/when-easter */

#include <stdio.h>

void easter(int y, int *m, int *d) {

*d = 225 - 11 * (y % 19);

while (*d > 50)
	*d -= 30;

if (*d > 48)
	--*d;

*d = *d + 7 - (y + y/4 + *d + 1) % 7;

if (*d > 31) {
	*m = 4;
	*d -= 31;
} else {
	*m = 3;
}

return 0;
}

int main( void ) {

int year, day, month;

for (year=1998; year<2100; year++) { // algorithm does not work after 2099
	easter(year,&month,&day);
	printf("%d-%02d-%02d\n", year, month, day);
}

return 0;
}

[kiranraaj19]

Interesting fact. Didnt know calculating a date would be this hectic of a task.

[R-CoderDotCom]

It seems to be difficult to calculate the easter day, but it is really easy to specify the day with special.days and highlight it

If you need to know if a year is a leap year or not you can use a simple script:

leap <- function(year){
  
  start <- as.Date(paste0(year,"-01-01"))
  end <- as.Date(paste0(year,"-12-31"))
  ndays <- length(seq(start, end, by="1 day"))
  
  return(ndays)
}

leap(2011)

[mschilli87]

@R-CoderDotCom:

Is there any case I am missing where this is better than the simple arithmetic solution?

leap <- function(year) {
  year <- as.integer(year)
  leap_every <- 4L
  leap_skip <- 100L
  leap_skip_skip <- leave_every * leap_skip_skip
  !(year %% leap_every) && (year %% leap_skip || !(year %% leap_skip_skip))
}