Arrays in PHP: Indexed, Associative & Multidimensional

Arrays in PHP

An array is a single variable that holds many values. Instead of creating ten separate variables for ten student names, you store them all in one array. PHP supports indexed arrays, associative arrays (key/value pairs), and arrays nested inside arrays.

Indexed arrays

An indexed array stores values in order, numbered starting from 0.

<?php
// Create an indexed array.
$subjects = ["PHP", "MySQL", "HTML"];

echo $subjects[0]; // PHP   (first item, index 0)
echo $subjects[2]; // HTML  (third item, index 2)

// Add an item to the end.
$subjects[] = "CSS";
?>

Associative arrays

An associative array uses named keys instead of numbers, which makes data easier to read.

<?php
// Each value has a meaningful key.
$student = [
    "name"   => "Kabir",
    "age"    => 20,
    "course" => "PHP & MySQL",
];

echo $student["name"];   // Kabir
echo $student["course"]; // PHP & MySQL
?>

Multidimensional arrays

You can put arrays inside arrays, which is useful for lists of records, such as rows from a database.

<?php
$students = [
    ["name" => "Anjali", "marks" => 88],
    ["name" => "Rohan",  "marks" => 76],
];

// Read the marks of the first student.
echo $students[0]["marks"]; // 88
?>

Looping over arrays

foreach is the cleanest way to read every item.

<?php
$fruits = ["Apple", "Mango", "Banana"];

foreach ($fruits as $fruit) {
    echo $fruit . "<br>";
}
?>

For associative arrays, capture both the key and the value:

<?php
$prices = ["pen" => 10, "book" => 60];

foreach ($prices as $item => $cost) {
    echo "$item costs $cost<br>";
}
?>

Useful array functions

PHP ships with many helpful functions for arrays. A few you will use often:

<?php
$numbers = [5, 2, 9, 1];

echo count($numbers);        // 4  -> number of items

array_push($numbers, 7);     // add 7 to the end
$last = array_pop($numbers); // remove and return the last item

sort($numbers);              // sort in ascending order
var_dump(in_array(9, $numbers)); // true -> is 9 present?
?>

Other handy functions include array_keys(), array_values(), array_merge(), and array_map().

Combining and searching

<?php
$a = ["red", "green"];
$b = ["blue", "yellow"];

$colors = array_merge($a, $b); // ["red", "green", "blue", "yellow"]

// Find the index of a value.
$position = array_search("blue", $colors); // 2
?>

Common mistakes

• Forgetting that indexes start at 0, so the first item is $array[0], not $array[1].
• Accessing a key that does not exist, which produces a warning. Check with isset() or array_key_exists() first.
• Confusing sort() with asort()/ksort(). sort() reindexes and discards keys; use asort() to keep associative keys.
• Using count() inside a loop condition repeatedly, which is wasteful. Store it in a variable when looping with for.

FAQ

What is the difference between an indexed and an associative array? Indexed arrays use numeric positions (0, 1, 2). Associative arrays use named keys you choose, like "name" or "age".

How do I count the items in an array? Use count($array). For nested counting, pass COUNT_RECURSIVE as the second argument.

How do I check if a key exists? Use isset($array["key"]) or array_key_exists("key", $array) to avoid undefined-key warnings.

Keep learning

Back to the PHP & MySQL hub, revisit Control Flow in PHP, or continue to Functions in PHP.

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