PHP Arrays

An array stores many values in one variable, such as a list of students or a price list.

Indexed Arrays

Items get numbers (indexes) starting from 0:

Example

php

<?php
$cities = ["Karachi", "Lahore", "Islamabad"];

echo $cities[0] . "<br>";
echo $cities[2] . "<br>";
echo "Number of cities: " . count($cities);

Output

Karachi
Islamabad
Number of cities: 3

Add an item to the end with []:

Example

php

<?php
$cities = ["Karachi", "Lahore"];
$cities[] = "Quetta";
print_r($cities);

Output

Array ( [0] => Karachi [1] => Lahore [2] => Quetta )

print_r() shows the whole array, which is helpful while testing.

Associative Arrays

Here you choose the keys yourself, usually as text:

Example

php

<?php
$student = [
    "name" => "Ayesha",
    "course" => "UI/UX",
    "fee_paid" => true,
];

echo $student["name"] . " studies " . $student["course"] . ".";

Output

Ayesha studies UI/UX.

Multidimensional Arrays

An array can contain other arrays. This is how data from a database usually looks:

Example

php

<?php
$products = [
    ["name" => "Mouse", "price" => 900],
    ["name" => "Keyboard", "price" => 1800],
    ["name" => "USB Cable", "price" => 350],
];

foreach ($products as $p) {
    echo $p["name"] . ": Rs " . $p["price"] . "<br>";
}

Output

Mouse: Rs 900
Keyboard: Rs 1800
USB Cable: Rs 350

Common Array Functions

Function	What it does
`count($a)`	Number of items
`in_array($v, $a)`	true if the value exists
`array_key_exists($k, $a)`	true if the key exists
`sort($a)` / `rsort($a)`	Sort values up / down
`asort($a)` / `ksort($a)`	Sort by value / by key, keeping keys
`array_push($a, $v)`	Add to the end
`array_pop($a)`	Remove from the end
`array_merge($a, $b)`	Join two arrays
`array_sum($a)`	Add all numbers
`implode(", ", $a)`	Join items into a string
`explode(",", $s)`	Split a string into an array

Example

php

<?php
$marks = [65, 92, 78, 50];
sort($marks);

echo implode(", ", $marks) . "<br>";
echo "Highest: " . max($marks) . "<br>";
echo in_array(92, $marks) ? "Someone got 92" : "No 92";

Output

50, 65, 78, 92
Highest: 92
Someone got 92

Filtering and Mapping

array_filter() keeps items that pass a test. array_map() changes every item.

Example

php

<?php
$prices = [200, 1500, 750, 3000];

$expensive = array_filter($prices, fn($p) => $p > 1000);
$withTax = array_map(fn($p) => $p * 1.1, $prices);

echo implode(", ", $expensive) . "<br>";
echo implode(", ", $withTax);

Output

1500, 3000
220, 1650, 825, 3300

sort() changes the original array and resets the keys. Use asort() if you want to keep the keys of an associative array.

Exercise

In $colors = ["red", "green", "blue"], what is $colors[1]?

redgreenblueAn error