PHP Arrays

What is an array in PHP?

When you need to store a list of related values, creating a separate variable for each one quickly becomes unmanageable. An array solves this by letting a single variable hold an ordered collection of values. Every value inside the array is paired with a key, and you use that key to read or change the value later. PHP is unusual in that its arrays are extremely flexible: the same array type is used for numbered lists, key-value maps, and nested structures.

The most common way to build an array is with the short square-bracket syntax introduced in PHP 5.4. The older array() function does exactly the same thing and still works, so you will see both styles in real projects.

<?php
$fruits = ["apple", "banana", "cherry"];

// The older, equivalent style
$colors = array("red", "green", "blue");

echo $fruits[0];   // apple
echo $colors[2];   // blue
?>

The three kinds of arrays

• Indexed arrays use automatic numeric keys starting at 0, which is ideal for ordered lists.
• Associative arrays use named string keys that you choose, which is ideal for records like a user profile.
• Multidimensional arrays store other arrays as their values, letting you model tables, grids, and nested data.

Under the hood these are all the same data type, so a single array can even mix numeric and string keys. To inspect what an array actually contains, print_r() and var_dump() are your best friends during development. count() tells you how many top-level elements an array holds.

<?php
$scores = [90, 85, 72];

echo count($scores);   // 3

print_r($scores);
/*
Array
(
    [0] => 90
    [1] => 85
    [2] => 72
)
*/
?>

Modifying an array

Arrays are not fixed in size. You can append a value by assigning to an empty bracket pair, which lets PHP pick the next numeric key for you, and you can overwrite an existing value by targeting its key directly.

<?php
$tasks = ["write code"];
$tasks[] = "review PR";      // appended at key 1
$tasks[] = "deploy";         // appended at key 2
$tasks[0] = "write tests";   // overwrites the first value

print_r($tasks);
// [write tests, review PR, deploy]
?>