Arrays: lists and key-value pairs

Store several values in indexed or associative arrays and manipulate them with PHP’s essential functions.

8 min · 3 questions

An array is a variable able to hold several values at once, like a shelf with multiple slots. In an indexed array, each slot is numbered by an index that starts at 0: the first element is therefore $colors[0]. You create an array with brackets [...], read a slot with $colors[index], and the syntax $colors[] = ... adds a new value at the end.

<?php

$colors = ["red", "green", "blue"];

echo $colors[0];
echo $colors[2];

$colors[] = "yellow";
$colors[1] = "purple";

echo count($colors);

Sometimes a number means nothing: to describe a person, labels are better. The associative array links a key (a name, often a string) to a value, with the arrow => that reads “corresponds to”. You then access a value by its key: $user["name"]. It’s PHP’s go-to structure for representing data.

<?php

$user = [
    "name" => "Awa",
    "age" => 28,
    "city" => "Lyon",
];

echo $user["name"];
echo $user["city"];

$user["age"] = 29;

PHP provides hundreds of ready-to-use array functions. Remember the essential ones: count($array) returns the number of elements; in_array($value, $array) answers true if the value is present; sort($array) sorts the array in place, from smallest to largest; implode($glue, $array) joins all elements into a single string, separated by the text of your choice; and array_keys($array) returns the list of keys.

<?php

$numbers = [8, 3, 5];
sort($numbers);

echo implode(" - ", $numbers);
echo "<br>";

$guests = ["Awa", "Bruno", "Chloe"];

if (in_array("Bruno", $guests)) {
    echo "Bruno is on the list.<br>";
}

echo count($guests);

Knowledge check

Make sure you remember the key points of this lesson.

1. What is the index of the first element of an indexed array?
   • 0
   • 1
   • -1
2. With $user = ["city" => "Lyon"], how do you read the value “Lyon”?
   • $user->city
   • $user["city"]
   • $user.city
3. What does count($colors) return?
   • The last element of the array
   • The number of elements in the array
   • The sum of the array values