Mastering PHP: From Basics to Building Dynamic Web Applications

Chapter 4: Arrays and Functions

🔹 1. Introduction

Arrays and functions are two essential building blocks in PHP.

• Arrays store multiple values in a single variable — ideal for data like lists, tables, and records.
• Functions allow you to write reusable, modular blocks of code, improving code efficiency and readability.

This chapter introduces both — starting from basic arrays to building your own functions.

🔹 2. Types of Arrays in PHP

PHP supports three main types of arrays:

✅ 1. Indexed Arrays

$colors = ["Red", "Green", "Blue"];

echo $colors[0]; // Red

✅ 2. Associative Arrays

$person = [

  "name" => "Alice",

  "age" => 28

];

echo $person["name"]; // Alice

✅ 3. Multidimensional Arrays

$users = [

  ["Alice", "alice@gmail.com"],

  ["Bob", "bob@yahoo.com"]

];

echo $users[1][0]; // Bob

🔹 3. Looping Through Arrays

✅ Indexed Array:

$fruits = ["Apple", "Banana", "Mango"];

foreach($fruits as $fruit){

  echo $fruit . "<br>";

}

✅ Associative Array:

$person = ["name" => "John", "age" => 30];

foreach($person as $key => $value){

  echo "$key: $value<br>";

}

🔹 4. Common Array Functions

✅ Example:

$nums = [5, 3, 8];

sort($nums);

print_r($nums); // [3, 5, 8]

🔹 5. Defining and Using Functions

✅ Basic Syntax:

function greet() {

  echo "Hello!";

}

greet(); // Output: Hello!

✅ Function With Parameters:

function sayHello($name) {

  echo "Hi, $name!";

}

sayHello("Jane");

✅ Default Parameters:

function welcome($name = "Guest") {

  echo "Welcome, $name!";

}

welcome(); // Welcome, Guest!

✅ Return Values:

function add($a, $b){

  return $a + $b;

}

$result = add(3, 5);

echo $result; // 8

🔹 6. Function Scope: Local vs Global

Variables declared inside functions are local to that function.

✅ Example:

$name = "Global";

function testScope(){

  $name = "Local";

  echo $name;

}

testScope(); // Local

echo $name;  // Global

✅ Use global keyword:

$x = 5;

$y = 10;

function sum(){

  global $x, $y;

  echo $x + $y;

}

sum(); // 15

🔹 7. Anonymous Functions & Callbacks

✅ Assigning functions to variables:

$greet = function($name) {

  return "Hello, $name!";

};

echo $greet("Jake");

✅ Using callbacks in array functions:

$nums = [1, 2, 3];

$squared = array_map(function($n){ return $n*$n; }, $nums);

print_r($squared); // [1, 4, 9]

🔹 8. Summary Table: Arrays & Functions