Given a year, report if it is a leap year.
The tricky thing here is that a leap year in the Gregorian calendar occurs:
on every year that is evenly divisible by 4 except every year that is evenly divisible by 100 unless the year is also evenly divisible by 400
For example, 1997 is not a leap year, but 1996 is. 1900 is not a leap year, but 2000 is.
Though our exercise adopts some very simple rules, there is more to learn!
For a delightful, four minute explanation of the whole leap year phenomenon, go watch this youtube video.
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JavaRanch Cattle Drive, exercise 3 http://www.javaranch.com/leap.jsp
(* leap - 1.5.1 *) open OUnit2 open Leap let ae exp got _test_ctxt = assert_equal exp got ~printer:string_of_bool let tests = [ "year not divisible by 4 in common year" >:: ae false (leap_year 2015); "year divisible by 2, not divisible by 4 in common year" >:: ae false (leap_year 1970); "year divisible by 4, not divisible by 100 in leap year" >:: ae true (leap_year 1996); "year divisible by 100, not divisible by 400 in common year" >:: ae false (leap_year 2100); "year divisible by 400 in leap year" >:: ae true (leap_year 2000); "year divisible by 200, not divisible by 400 in common year" >:: ae false (leap_year 1800); ] let () = run_test_tt_main ("leap tests" >::: tests)
(* util *) let (~!) = not let (%?) a b = a mod b = 0 (* solution *) let leap_year y = (y %? 4) && ~!(y %? 100) || (y %? 400)
val ( ~! ) : bool -> bool val ( %? ) : int -> int -> bool val leap_year : int -> bool
A huge amount can be learned from reading other people’s code. This is why we wanted to give exercism users the option of making their solutions public.
Here are some questions to help you reflect on this solution and learn the most from it.