Language List#

Welcome to Language List on Exercism's PHP Track. If you need help running the tests or submitting your code, check out HELP.md. If you get stuck on the exercise, check out HINTS.md, but try and solve it without using those first :)

Introduction#

Arrays#

Arrays in PHP are ordered maps. A map is a data structure that associates a key to a value. Arrays are versatile and can be treated as a linear array (like in C or Java), list [vector], hash-table, dictionary, collection, stack, or a queue.

A key is optional, but if specified must either be an int or a string. When a key is not provided, PHP defaults to integer keys in increasing order, starting at 0.

$no_keys = ["my", "first", "array"];
$integer_keys = [0 => "my", 1 => "first", 2 => "array"];

$no_keys == $integer_keys // => equal returns true
$no_keys === $integer_keys // => strictly equal returns true

An array can store values of all types. Each value can have a different type.

Using Arrays#

Arrays can be declared as a literal (written in code, as done above) or created and manipulated as functions. Access, assign, append values using the index operator:

$prime_numbers = [2, 3, 5, 6];

$prime_numbers[3] = 7; // replace 6 with 7

$prime_numbers[] = 11; // array now contains [2, 3, 5, 7, 11]

Variable-Length Arguments#

Function arguments can be specified such that it can take any number of arguments:

<?php

function actOnItems(...$items) {
  // $items is an array containing 0 or more values
  // used to call the function.
}

actOnItems(1, 2, 3, 4); // $items => [1, 2, 3, 4]

Instructions#

In this exercise you need to implement some functions to manipulate a list of programming languages.

1. Define a function to return an empty language list#

Define the language_list function that takes no arguments and returns an empty list.

<?php

language_list();
// => []

2. Modify function to create a list from any number of languages#

Modify the language_list function, so it takes a variadic argument of languages (strings). It should return the resulting list with the languages in the list.

<?php

$language_list = language_list();
// => []
$language_list = language_list("Clojure", "PHP");
// => ["Clojure", "PHP"]
$language_list = language_list("PHP", "Haskell", "Java", "C++", "Rust")
// => ["PHP", "Haskell", "Java", "C++", "Rust"]

3. Define a function to add a language to the list#

Define the add_to_language_list function that takes 2 arguments, an array of languages, and the new language.

<?php

$language_list = language_list();
// => []
$language_list = add_to_language_list($language_list, "Clojure");
// => ["Clojure"]

4. Define a function to remove an item from the language list#

Define the prune_language_list function to remove the first language from the array of languages.

<?php

$language_list = language_list("PHP");
// => ["PHP"]
$language_list = prune_language_list($language_list);
// => []

5. Define a function to get the first item in the list#

Define the current_language function that takes 1 argument (a language list). It should return the first language in the list. Assume the list will always have at least one item.

<?php

$language_list = language_list("PHP", "Prolog");
// => ["PHP", "Prolog"]
$first = current_language($language_list);
// => "PHP"

6. Define a function to return how many languages are in the list#

Define the language_list_length function that takes 1 argument (a language list). It should return the number of languages in the list.

<?php

$language_list = language_list("PHP", "Prolog", "Wren");
// => ["PHP", "Prolog", "Wren"]
language_list_length($language_list);
// => 3

Source#

Created by#

• @neenjaw