PHP Arrays: Create, Access, Loop and Print

A PHP array stores a list of values under keys. Create one with square brackets, $fruits = ['apple', 'banana', 'cherry'];, and read an element by its index, $fruits[0]. Indexes start at 0, and count($fruits) gives the number of elements.

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

echo $fruits[0], "\n";        // first element
echo $fruits[2], "\n";        // third element
echo count($fruits), "\n";    // number of elements

$fruits[] = 'date';           // add to the end
$fruits[1] = 'blueberry';     // change an element

print_r($fruits);

Every PHP array is an ordered map: each value sits under a key. When you do not choose the keys, PHP numbers them 0, 1, 2... and you get an indexed array. When you choose them yourself (['name' => 'Ada']), you get an associative array. Both are the same array type.

Create an array

Square brackets are the usual syntax. array() is the older spelling and produces exactly the same thing. range() builds a list of numbers or letters, and array_fill() repeats one value.

<?php
$empty   = [];
$numbers = [10, 20, 30];
$old     = array('a', 'b', 'c');      // same as ['a', 'b', 'c']
$mixed   = [1, 'two', 3.5, true, null];

$oneToFive = range(1, 5);
$letters   = range('a', 'e');
$zeros     = array_fill(0, 3, 0);

echo implode(', ', $oneToFive), "\n";
echo implode(', ', $letters), "\n";
echo implode(', ', $zeros), "\n";
var_dump($empty === []);
echo count($mixed), "\n";

A PHP array can hold values of different types at once, including other arrays. An array of arrays is a multidimensional array, the usual way to hold rows of data.

Get the first and last element

PHP has no negative indexes. $arr[-1] does not mean "the last one": it looks up a key named -1 and, when there is none, PHP prints Warning: Undefined array key -1. Use array_key_first() and array_key_last(), which also work when the keys do not start at 0.

<?php
$queue = ['Ada', 'Grace', 'Linus', 'Margaret'];

$first = $queue[array_key_first($queue)];
$last  = $queue[array_key_last($queue)];
echo "First: $first, last: $last\n";

// Same result by position
echo $queue[count($queue) - 1], "\n";

// The last two elements
print_r(array_slice($queue, -2));

end($queue) also returns the last value, but it moves the array's internal pointer as a side effect, so the key-based version is the clearer choice.

Print an array

echo $arr does not work: it prints the word Array and a warning. Pick the output that fits the job:

• print_r($arr) for a readable dump while debugging.
• var_dump($arr) to also see each value's type and length.
• implode(', ', $arr) to turn the values into one string for display.
• json_encode($arr) to send the array to JavaScript or an API.

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

print_r($scores);
var_dump($scores);
echo implode(', ', $scores), "\n";
echo json_encode($scores), "\n";

The print_r and var_dump page covers the formatting options, including printing an array inside HTML.

Loop over an array

foreach is the loop made for arrays: it hands you each value, and the key too if you ask for it. A for loop with an index also works for indexed arrays whose keys run from 0 without gaps.

<?php
$languages = ['PHP', 'Python', 'Go'];

foreach ($languages as $language) {
    echo "I know $language\n";
}

foreach ($languages as $i => $language) {
    echo ($i + 1) . ". $language\n";
}

for ($i = 0; $i < count($languages); $i++) {
    echo strtolower($languages[$i]), "\n";
}

Arrays are copied, not shared

Assigning an array to another variable, or passing it to a function, gives a copy. Changing the copy leaves the original alone. Add & to the parameter when a function should change the caller's array.

<?php
$a = [1, 2, 3];
$b = $a;          // a copy
$b[] = 4;

echo count($a), " ", count($b), "\n";

function addItem(array &$list, string $item): void
{
    $list[] = $item;
}

$cart = ['milk'];
addItem($cart, 'bread');
print_r($cart);

Array functions by task

PHP ships more than 70 array functions. These are the ones you will use most, each with its own page:

Keys that silently merge

Array keys are either integers or strings, and PHP converts some keys for you. A string that looks like a whole decimal number, such as "1", becomes the integer 1, so $a["1"] and $a[1] are the same slot. "01" and "1.5" stay strings. This is why an array built from form input or a CSV can end up with fewer elements than you expected.

<?php
$a = [];
$a[1]    = 'int one';
$a["1"]  = 'string one';   // same key as 1, overwrites it
$a["01"] = 'zero one';     // stays the string "01"

var_dump($a);
echo count($a), "\n";