Strings and Arrays

The workhorse data types

A PHP array is an ordered map: keys can be integers or strings, and the same type serves as a list, a dictionary, a stack and a queue. Lists use sequential integer keys (array_is_list() checks this). Useful functions: count, in_array (use the strict third argument), array_key_exists, array_map, array_filter (keeps original keys, so wrap with array_values to reindex), array_reduce, array_column, array_combine, usort with a comparison closure using the spaceship operator <=>, array_slice, array_merge and the spread syntax [...$a, ...$b]. Destructuring works with [$a, $b] = $pair and ['id' => $id] = $row. Strings are byte strings: functions like strlen and substr count bytes, so for user-visible text in languages such as Hindi use the mb_* functions (mb_strlen, mb_substr, mb_strtoupper) with UTF-8. PHP 8 added str_contains, str_starts_with and str_ends_with. Use sprintf or number_format for formatting, and explode/implode to split and join.

Arrays and multibyte strings in practice

Group, sort and summarise orders; count characters correctly in Hindi.

<?php
declare(strict_types=1);

$orders = [
    ['id' => 'o-1', 'city' => 'Pune',  'total' => 1200.0],
    ['id' => 'o-2', 'city' => 'Delhi', 'total' => 300.0],
    ['id' => 'o-3', 'city' => 'Pune',  'total' => 800.0],
];

$big = array_values(array_filter($orders, fn (array $o): bool => $o['total'] >= 500));
usort($big, fn (array $a, array $b): int => $b['total'] <=> $a['total']);   // descending

$byCity = [];
foreach ($orders as ['city' => $city, 'total' => $total]) {               // destructuring
    $byCity[$city] = ($byCity[$city] ?? 0) + $total;
}

$ids = array_column($orders, 'id');                // ['o-1', 'o-2', 'o-3']
$hasPune = in_array('Pune', array_column($orders, 'city'), true);

$word = 'नमस्ते';
echo strlen($word), ' bytes, ', mb_strlen($word), ' characters', PHP_EOL;
echo str_contains('order-2026', '2026') ? 'found' : 'missing', PHP_EOL;

array_filter keeps keys

After filtering [0 => a, 1 => b, 2 => c] down to a and c, the keys are 0 and 2. JSON-encoding that produces an object, not a list. Wrap the result in array_values() when you need a list.

Quick check: Why use mb_strlen instead of strlen for user-entered text in Hindi?

• strlen counts bytes, while mb_strlen counts characters in multibyte encodings such as UTF-8
• strlen is deprecated
• mb_strlen is faster for ASCII
• strlen only works on numbers