PHP Array Basics

Arrays are one of the most powerful and frequently used data structures in PHP. They allow you to store multiple values in a single variable, making it easy to work with collections of related data like user lists, product catalogs, or configuration settings.

What is an Array?

An array is an ordered collection of values. Each value is called an element, and each element has a position called an index or key.

Creating Indexed Arrays

Indexed arrays use numeric keys starting from 0:

<?php
// Modern short syntax (recommended)
$fruits = ["Apple", "Banana", "Cherry"];

// Traditional syntax
$colors = array("Red", "Green", "Blue");

// Empty array
$empty = [];

// Both syntaxes create identical arrays
var_dump($fruits);
// array(3) { [0]=> "Apple" [1]=> "Banana" [2]=> "Cherry" }
?>

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Accessing Array Elements

Use square brackets with the index to access elements:

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

echo $fruits[0];  // Apple (first element)
echo $fruits[1];  // Banana (second element)
echo $fruits[3];  // Date (fourth element)

// Get the last element
$lastIndex = count($fruits) - 1;
echo $fruits[$lastIndex];  // Date

// Or use end() function
echo end($fruits);  // Date (moves internal pointer)
?>

Modifying Arrays

Arrays in PHP are mutable - you can change, add, or remove elements:

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

// Modify existing element
$fruits[1] = "Blueberry";
// ["Apple", "Blueberry", "Cherry"]

// Add element at specific index
$fruits[3] = "Date";
// ["Apple", "Blueberry", "Cherry", "Date"]

// Append element (auto-assigns next index)
$fruits[] = "Elderberry";
// ["Apple", "Blueberry", "Cherry", "Date", "Elderberry"]

// Remove element
unset($fruits[2]);
// ["Apple", "Blueberry", "Date", "Elderberry"]
// Note: indices don't reindex! Index 2 is now missing
?>

Associative Arrays

Associative arrays use string keys instead of numeric indices:

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Associative Array Syntax

<?php
// Creating associative arrays
$person = [
    "name" => "John Doe",
    "age" => 30,
    "email" => "[email protected]"
];

// Accessing values
echo $person["name"];   // John Doe
echo $person["age"];    // 30

// Adding new key-value pair
$person["city"] = "New York";

// Modifying existing value
$person["age"] = 31;

// Removing a key
unset($person["email"]);
?>

Useful Array Functions

Quick Array Creation

<?php
// Create array of numbers
$numbers = range(1, 10);
// [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]

// Create array with step
$evens = range(2, 10, 2);
// [2, 4, 6, 8, 10]

// Create array of letters
$letters = range('a', 'f');
// ['a', 'b', 'c', 'd', 'e', 'f']

// Create array with repeated value
$zeros = array_fill(0, 5, 0);
// [0, 0, 0, 0, 0]

// Create array from variables
$a = 1; $b = 2; $c = 3;
$arr = compact('a', 'b', 'c');
// ["a" => 1, "b" => 2, "c" => 3]
?>

Printing Arrays

<?php
$arr = ["name" => "John", "age" => 30];

// print_r - Human-readable output
print_r($arr);
/*
Array
(
    [name] => John
    [age] => 30
)
*/

// var_dump - Detailed output with types
var_dump($arr);
/*
array(2) {
  ["name"]=> string(4) "John"
  ["age"]=> int(30)
}
*/

// JSON format
echo json_encode($arr);
// {"name":"John","age":30}
?>

Common Mistakes

<?php
$arr = ["a", "b", "c"];  // Indices: 0, 1, 2

// ❌ WRONG: Index 3 doesn't exist
echo $arr[3];  // Warning: Undefined array key 3

// ✅ CORRECT: Use valid indices
echo $arr[2];  // "c" (last element)
echo $arr[count($arr) - 1];  // "c"
?>

<?php
$person = ["name" => "John"];

// ❌ WRONG: Using variable syntax without quotes
echo $person[name];  // Notice: Use of undefined constant

// ✅ CORRECT: Always quote string keys
echo $person["name"];  // John
echo $person['name'];  // John (also valid)
?>

<?php
$arr = ["a", "b", "c"];  // [0=>"a", 1=>"b", 2=>"c"]
unset($arr[1]);
// Now: [0=>"a", 2=>"c"] - Index 1 is MISSING!

print_r($arr);
// Array ( [0] => a [2] => c )

// To reindex after unset:
$arr = array_values($arr);
// Now: [0=>"a", 1=>"c"]
?>

Exercise: Contact List

<?php
// Create contact list
$contacts = [
    [
        "name" => "Alice Smith",
        "email" => "[email protected]",
        "phone" => "555-1234"
    ],
    [
        "name" => "Bob Johnson",
        "email" => "[email protected]",
        "phone" => "555-5678"
    ],
    [
        "name" => "Carol Williams",
        "email" => "[email protected]",
        "phone" => "555-9012"
    ]
];

// Display all contacts
echo "=== Contact List ===\n\n";
foreach ($contacts as $index => $contact) {
    echo ($index + 1) . ". {$contact['name']}\n";
    echo "   Email: {$contact['email']}\n";
    echo "   Phone: {$contact['phone']}\n\n";
}

// Find contact by name
$searchName = "Bob Johnson";
$found = null;

foreach ($contacts as $contact) {
    if ($contact['name'] === $searchName) {
        $found = $contact;
        break;
    }
}

if ($found) {
    echo "Found: {$found['name']} ({$found['email']})\n";
} else {
    echo "Contact not found.\n";
}
?>

Summary

What's Next?

Now that you understand basic arrays, let's explore Multidimensional Arrays - arrays within arrays that let you represent complex data structures!