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.
If your language provides a method in the standard library that does this look-up, pretend it doesn't exist and implement it yourself.
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.
JavaRanch Cattle Drive, exercise 3 http://www.javaranch.com/leap.jsp
It's possible to submit an incomplete solution so you can see how others have completed the exercise.
;;; leap-test.el --- Tests for Leap exercise (exercism) ;;; Commentary: ;;; Code: (load-file "leap.el") (ert-deftest vanilla-leap-year () (should (leap-year-p 1996))) (ert-deftest any-old-year () (should-not (leap-year-p 1997))) (ert-deftest non-leap-even-year () (should-not (leap-year-p 1997))) (ert-deftest century () (should-not (leap-year-p 1900))) (ert-deftest exceptional-century () (should (leap-year-p 2000))) (provide 'leap-test) ;;; leap-test.el ends here
;;; leap.el --- Leap exercise (exercism) ;;; Commentary: ;;; Code: ;; 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 (defun is-mod-0 (v1 v2) "Check V1%V2 == 0." (eq (mod v1 v2) 0)) (defun leap-year-p (year) "Return t if YEAR is leap." (or (is-mod-0 year 400) (and (is-mod-0 year 4) (not (is-mod-0 year 100))))) (provide 'leap-year-p) ;;; leap.el ends here
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.