PHP Programming Notes

1. Introduction to PHP

1.1 What is PHP?

PHP stands for Hypertext Preprocessor, which is a popular server-side scripting language used to create dynamic web pages.
It is embedded into HTML to produce dynamic content, like interacting with databases, handling forms, and performing server-side operations.
PHP is open-source and runs on most servers, like Apache and Nginx.

1.2 Syntax of PHP

A PHP script starts with <?php and ends with ?>. PHP code can be embedded into an HTML file.

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

2. PHP Variables

2.1 Declaring Variables

Variables in PHP are declared using a dollar sign ($) followed by the variable name.

<?php
    $name = "John";
    $age = 25;
    echo $name;
?>

2.2 Data Types in PHP

String: A sequence of characters.
Integer: A whole number.
Float: A decimal number.
Boolean: Represents true or false.
Array: An ordered collection of values.
Object: An instance of a class.

<?php
    $name = "John";  // String
    $age = 25;       // Integer
    $price = 19.99;  // Float
    $is_student = true;  // Boolean
?>

3. PHP Operators

3.1 Arithmetic Operators

These operators perform basic mathematical operations.

<?php
    $sum = 10 + 5;    // Addition
    $diff = 10 - 5;   // Subtraction
    $prod = 10 * 5;   // Multiplication
    $quotient = 10 / 5;  // Division
    $remainder = 10 % 3; // Modulus
?>

3.2 Relational Operators

Used to compare two values.

<?php
    $isEqual = (10 == 5);    // Equal to
    $isNotEqual = (10 != 5); // Not equal to
    $isGreaterThan = (10 > 5); // Greater than
    $isLessThan = (10 < 5);    // Less than
?>

3.3 Logical Operators

Used for logical operations.

<?php
    $and = (true && false); // AND
    $or = (true || false);  // OR
    $not = !true;           // NOT
?>

4. PHP Control Structures

4.1 If-Else Statement

The if-else statement is used to execute code conditionally.

<?php
    $age = 18;
    if ($age >= 18) {
        echo "You are eligible to vote.";
    } else {
        echo "You are not eligible to vote.";
    }
?>

4.2 Switch-Case Statement

The switch-case statement is used for multi-way branching.

<?php
    $day = 3;
    switch ($day) {
        case 1:
            echo "Monday";
            break;
        case 2:
            echo "Tuesday";
            break;
        case 3:
            echo "Wednesday";
            break;
        default:
            echo "Invalid day";
    }
?>

4.3 Loops in PHP

For loop: Executes a block of code a fixed number of times.

<?php
    for ($i = 0; $i < 5; $i++) {
        echo $i;
    }
?>

While loop: Executes as long as the condition is true.

<?php
    $i = 0;
    while ($i < 5) {
        echo $i;
        $i++;
    }
?>

Do-While loop: Executes at least once and then checks the condition.

<?php
    $i = 0;
    do {
        echo $i;
        $i++;
    } while ($i < 5);
?>

5. PHP Functions

5.1 Defining Functions

A function is a block of code that can be called to perform a specific task.

<?php
    function greet() {
        echo "Hello, welcome to PHP!";
    }
    greet();  // Calling the function
?>

5.2 Functions with Parameters

Functions can accept parameters to make them more dynamic.

<?php
    function greet($name) {
        echo "Hello, " . $name . "!";
    }
    greet("John");  // Output: Hello, John!
?>

6. Arrays in PHP

6.1 Indexed Arrays

An indexed array stores values with numeric indices.

<?php
    $fruits = array("Apple", "Banana", "Cherry");
    echo $fruits[0];  // Output: Apple
?>

6.2 Associative Arrays

An associative array stores values with named keys.

<?php
    $person = array("name" => "John", "age" => 25);
    echo $person["name"];  // Output: John
?>

6.3 Multidimensional Arrays

Arrays containing other arrays.

<?php
    $students = array(
        array("John", 25),
        array("Jane", 22)
    );
    echo $students[0][0];  // Output: John
?>

7. PHP Forms Handling

7.1 Getting Form Data Using `$_GET`

When a form is submitted with method GET, the data is sent in the URL.

<form method="GET" action="process.php">
    Name: <input type="text" name="name">
    <input type="submit">
</form>

<?php
    // process.php
    echo $_GET['name'];
?>

7.2 Getting Form Data Using `$_POST`

When a form is submitted with method POST, the data is sent in the HTTP body.

<form method="POST" action="process.php">
    Name: <input type="text" name="name">
    <input type="submit">
</form>

<?php
    // process.php
    echo $_POST['name'];
?>

8. File Handling in PHP

8.1 Writing to a File

<?php
    $file = fopen("file.txt", "w");
    fwrite($file, "Hello, PHP file handling!");
    fclose($file);
?>

8.2 Reading from a File

<?php
    $file = fopen("file.txt", "r");
    $content = fread($file, filesize("file.txt"));
    echo $content;
    fclose($file);
?>

9. Object-Oriented Programming (OOP) in PHP

9.1 Classes and Objects

A class is a blueprint for objects.

<?php
    class Car {
        public $model;
        public $color;

        function __construct($model, $color) {
            $this->model = $model;
            $this->color = $color;
        }

        function displayDetails() {
            echo "Model: " . $this->model . "<br>";
            echo "Color: " . $this->color;
        }
    }

    $car1 = new Car("Toyota", "Red");
    $car1->displayDetails();
?>

9.2 Inheritance

Inheritance allows a class to inherit properties and methods from another class.

<?php
    class Animal {
        public $name;

        function __construct($name) {
            $this->name = $name;
        }

        function speak() {
            echo $this->name . " makes a sound.<br>";
        }
    }

    class Dog extends Animal {
        function speak() {
            echo $this->name . " barks.<br>";
        }
    }

    $dog = new Dog("Buddy");
    $dog->speak();  // Output: Buddy barks.
?>

10. Exception Handling in PHP

10.1 Try-Catch Block

Exception handling is done using try-catch blocks.

<?php
    try {
        $result = 10 / 0;
    } catch (Exception $e) {
        echo "Error: " . $e->getMessage();
    }
?>

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PHP (Hypertext Preprocessor Notes)