Published at Nov 13 2018
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Instructions

Test suite

Solution

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.

For installation and learning resources, refer to the exercism help page.

To work on the exercises, you will need `Opam`

and `Base`

. Consult opam website for instructions on how to install `opam`

for your OS. Once `opam`

is installed open a terminal window and run the following command to install base:

```
opam install base
```

To run the tests you will need `OUnit`

. Install it using `opam`

:

```
opam install ounit
```

A Makefile is provided with a default target to compile your solution and run the tests. At the command line, type:

```
make
```

`utop`

is a command line program which allows you to run Ocaml code interactively. The easiest way to install it is via opam:

```
opam install utop
```

Consult utop for more detail.

The exercism/ocaml repository on GitHub is the home for all of the Ocaml exercises.

If you have feedback about an exercise, or want to help implementing a new one, head over there and create an issue. We'll do our best to help you!

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.

```
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: common year" >::
ae false (leap_year 2015);
"year divisible by 4, not divisible by 100: leap year" >::
ae true (leap_year 1996);
"year divisible by 100, not divisible by 400: common year" >::
ae false (leap_year 2100);
"year divisible by 400: leap year" >::
ae true (leap_year 2000);
"year divisible by 200, not divisible by 400: common year" >::
ae false (leap_year 1800);
]
let () =
run_test_tt_main ("leap tests" >::: tests)
```

```
let leap_year y =
y mod 4 = 0 && (y mod 100 <> 0 || y mod 400 = 0)
```

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.

- What compromises have been made?
- Are there new concepts here that you could read more about to improve your understanding?

## Community comments