1. Introduction to PHP

PHP (Hypertext Preprocessor) is a widely-used open-source scripting language designed primarily for web development. It runs on the server side and is embedded into HTML, making it an essential language for dynamic and interactive web applications.

2. Basic Syntax

PHP scripts start with <?php and end with ?>. Statements end with a semicolon (;).

<?php
echo "Hello, World!";
?>

Case Sensitivity

• Keywords (e.g., if, else, while) are not case-sensitive.

• Variable names are case-sensitive.

3. Variables

Variables store data and are defined using the $ symbol.

$name = "John";
$age = 30;

Variable Scope

• Local: Declared inside a function, accessible only within.

• Global: Declared outside functions, can be accessed using global or $GLOBALS.

• Static: Retains value between function calls.

• Superglobal: Special predefined variables like $_POST, $_GET.

4. Data Types

PHP supports multiple data types:

• String: "Hello"

• Integer: 123

• Float: 3.14

• Boolean: true/false

• Array: array("apple", "banana")

• Object: Defined from a class.

• NULL: Represents no value.

• Resource: Holds references to external resources like database connections.

5. Operators

Arithmetic Operators

$sum = 5 + 3; // Addition
$sub = 5 - 3; // Subtraction
$mul = 5 * 3; // Multiplication
$div = 5 / 3; // Division
$mod = 5 % 3; // Modulus

Comparison Operators

$a == $b  // Equal
$a === $b // Identical (same value & type)
$a != $b  // Not equal
$a < $b   // Less than
$a > $b   // Greater than

Logical Operators

$a && $b // AND
$a || $b // OR
!$a      // NOT

Assignment Operators

$x += 5; // Equivalent to $x = $x + 5;
$x -= 5; // Equivalent to $x = $x - 5;

6. Control Structures

Conditional Statements

if ($age > 18) {
    echo "Adult";
} elseif ($age == 18) {
    echo "Just turned adult";
} else {
    echo "Minor";
}

Switch Statement

$day = "Monday";
switch ($day) {
    case "Monday":
        echo "Start of the week";
        break;
    case "Friday":
        echo "Weekend coming";
        break;
    default:
        echo "Regular day";
}

Loops

// While loop
$i = 1;
while ($i <= 5) {
    echo $i;
    $i++;
}

// For loop
for ($i = 1; $i <= 5; $i++) {
    echo $i;
}

// Foreach loop (for arrays)
$fruits = ["apple", "banana"];
foreach ($fruits as $fruit) {
    echo $fruit;
}

7. Functions

User-defined functions enhance code reusability.

function greet($name) {
    return "Hello, " . $name;
}
echo greet("Alice");

8. Arrays

Arrays store multiple values in a single variable.

Indexed Array

$colors = ["red", "blue", "green"];
echo $colors[0]; // Outputs "red"

Associative Array

$ages = ["Alice" => 25, "Bob" => 30];
echo $ages["Alice"]; // Outputs 25

Multidimensional Array

$students = [
    ["John", 20],
    ["Jane", 22]
];
echo $students[0][0]; // Outputs "John"

9. Strings

String manipulation is essential in PHP.

$name = "John Doe";
echo strlen($name); // String length
echo str_replace("Doe", "Smith", $name); // Replace substring

10. Superglobals

PHP provides predefined global arrays:

• $_GET – Collects data from a form (via URL parameters).

• $_POST – Collects form data via HTTP POST.

• $_SESSION – Stores user session data.

• $_COOKIE – Stores user cookies.

11. File Handling

$file = fopen("test.txt", "r");
echo fread($file, filesize("test.txt"));
fclose($file);

12. Object-Oriented Programming (OOP)

Class & Object

class Car {
    public $brand;
    function __construct($brand) {
        $this->brand = $brand;
    }
    function getBrand() {
        return $this->brand;
    }
}
$myCar = new Car("Toyota");
echo $myCar->getBrand();

13. Error Handling

try {
    throw new Exception("Error occurred");
} catch (Exception $e) {
    echo $e->getMessage();
}

14. Database Connection (MySQLi)

$conn = new mysqli("localhost", "root", "", "testdb");
if ($conn->connect_error) {
    die("Connection failed: " . $conn->connect_error);
}

15. Sessions and Cookies

Session

session_start();
$_SESSION["user"] = "John Doe";
echo $_SESSION["user"];

Cookie

setcookie("username", "John", time() + (86400 * 30), "/");

PHP is a versatile language for web development, offering features like database interaction, OOP, and security mechanisms. Mastering these elements allows developers to build robust and efficient web applications.