Mastering PHP: Web Development Practices

Mastering PHP

Web Development Practices

Copyright © 2024 by HiTeX Press

All rights reserved. No part of this publication may be reproduced, distributed, or transmitted in any form or by any means, including photocopying, recording, or other electronic or mechanical methods, without the prior written permission of the publisher, except in the case of brief quotations embodied in critical reviews and certain other noncommercial uses permitted by copyright law.

Contents

1 Introduction to PHP

1.1 History and Evolution of PHP

1.2 What is PHP?

1.3 Installing PHP

1.4 Setting Up a Local Development Environment

1.5 Your First PHP Script

1.6 Basic Syntax of PHP

1.7 PHP Tags and Escaping from HTML

1.8 Variables and Constants in PHP

1.9 Embedding PHP in HTML

1.10 Comments in PHP

1.11 Basic Output with echo and print

2 Variables and Data Types

2.1 Introduction to Variables

2.2 Declaring Variables

2.3 Variable Naming Conventions

2.4 Variable Scope

2.5 Global and Local Variables

2.6 Constants in PHP

2.7 Data Types in PHP

2.8 Type Juggling and Type Casting

2.9 Superglobals in PHP

2.10 Variable Variables

2.11 Static Variables

2.12 Common Variable Operations

3 Control Structures

3.1 Introduction to Control Structures

3.2 If, Elseif, and Else Statements

3.3 Switch Statements

3.4 Ternary Operator

3.5 While Loops

3.6 Do-While Loops

3.7 For Loops

3.8 Foreach Loops

3.9 Break and Continue Statements

3.10 Using control structures with HTML

3.11 Nested Control Structures

3.12 Alternative Syntax for Control Structures

4 Functions

4.1 Introduction to Functions

4.2 Defining and Calling Functions

4.3 Function Arguments

4.4 Returning Values from Functions

4.5 Variable Scope in Functions

4.6 Recursive Functions

4.7 Anonymous Functions and Closures

4.8 Built-in PHP Functions

4.9 Creating Custom Functions

4.10 Function Overloading

4.11 Default Parameters

4.12 Strict Type Declarations

5 Working with Arrays

5.1 Introduction to Arrays

5.2 Types of Arrays

5.3 Creating and Initializing Arrays

5.4 Accessing Array Elements

5.5 Looping Through Arrays

5.6 Multidimensional Arrays

5.7 Array Functions

5.8 Sorting Arrays

5.9 Merging Arrays

5.10 Splitting Arrays

5.11 Array Filtering

5.12 Array Mapping and Reducing

6 String Manipulation

6.1 Introduction to Strings

6.2 Creating and Accessing Strings

6.3 String Concatenation

6.4 String Functions

6.5 String Length

6.6 Finding and Replacing Substrings

6.7 String Formatting

6.8 String Splitting and Joining

6.9 Comparing Strings

6.10 Multibyte String Functions

6.11 Regular Expressions

6.12 Escaping Characters

7 Form Handling and Validation

7.1 Introduction to Form Handling

7.2 Creating HTML Forms

7.3 Form Submission Methods: GET and POST

7.4 Accessing Form Data with PHP

7.5 Validating Form Data

7.6 Sanitizing and Escaping User Input

7.7 Handling Multiple Form Elements

7.8 File Uploads through Forms

7.9 Form Security: CSRF Protection

7.10 Form Validation with Regular Expressions

7.11 Displaying Form Validation Errors

7.12 Persisting Form Data with Sessions and Cookies

8 Working with Databases

8.1 Introduction to Databases

8.2 Setting Up a Database Server

8.3 Connecting to a Database with PHP

8.4 Executing SQL Queries

8.5 Retrieving Data from a Database

8.6 Inserting Data into a Database

8.7 Updating and Deleting Database Records

8.8 Prepared Statements and Parameterized Queries

8.9 Handling Database Errors

8.10 Using PDO for Database Access

8.11 Database Transactions

8.12 Database Security and Injection Prevention

9 Object-Oriented Programming in PHP

9.1 Introduction to Object-Oriented Programming

9.2 Classes and Objects

9.3 Properties and Methods

9.4 Constructors and Destructors

9.5 Inheritance

9.6 Encapsulation

9.7 Polymorphism

9.8 Interfaces and Abstract Classes

9.9 Traits in PHP

9.10 Static Methods and Properties

9.11 Namespaces

9.12 Autoloading Classes

9.13 Exception Handling in OOP

10 Error Handling and Debugging

10.1 Introduction to Error Handling

10.2 Types of Errors in PHP

10.3 Basic Error Handling with die() and exit()

10.4 Error Reporting Levels

10.5 Custom Error Handling

10.6 Exception Handling

10.7 Using try, catch, and finally

10.8 Creating Custom Exception Classes

10.9 Logging Errors

10.10 Displaying Errors for Development

10.11 Suppressing Errors

10.12 Debugging Techniques and Tools

10.13 Profiling and Performance Analysis

Introduction

PHP, short for Hypertext Preprocessor, is a widely-used open-source server-side scripting language specifically designed for web development. Introduced in 1995 by Rasmus Lerdorf, PHP has evolved significantly over the years, becoming a cornerstone of modern web development. Its primary function is to generate dynamic content, making web pages interactive and responsive to user input.

This book aims to provide a thorough understanding of PHP, suitable for beginners who wish to master web development practices. The content is structured to guide the reader from fundamental concepts to more advanced topics, ensuring a comprehensive grasp of PHP’s capabilities.

Before delving into the technical aspects, it is essential to understand PHP’s role in web development. PHP scripts are executed on the server, and the result is returned to the browser as plain HTML. This server-side execution makes PHP a powerful tool for creating dynamic web pages that can interact with databases, handle forms, and manage sessions.

The installation and setup of a local development environment are the first steps in mastering PHP. This process involves installing a web server, PHP, and a database management system, typically using software bundles like XAMPP or WampServer. Setting up this environment will allow you to write, test, and debug PHP scripts efficiently.

Your journey begins with writing a simple PHP script, which is a quintessential part of learning any programming language. Understanding the basic syntax, such as PHP tags, comments, and basic output functions like ‘echo‘ and ‘print‘, is crucial at this stage. These elements form the foundation upon which more complex scripts will be built.

One of PHP’s strengths is its ability to seamlessly integrate with HTML. This integration allows for dynamic content generation, where PHP can manipulate HTML elements to create interactive web pages. Learning how to embed PHP within HTML is an essential skill for any web developer.

As you progress, you will encounter variables and constants, which are fundamental building blocks in PHP programming. Variables are used to store data, while constants hold values that remain unchanged throughout the script. Understanding variable scope and how to handle global and local variables is vital for writing efficient and error-free code.

This book also covers advanced topics such as control structures, which include conditional statements and loops. These structures enable you to control the flow of your scripts, making decisions based on specific conditions and repeating actions as needed.

Functions are another critical aspect of PHP, allowing you to encapsulate code into reusable blocks. This not only makes your code more organized but also enhances its readability and maintainability. You will learn how to define, call, and pass arguments to functions, as well as explore advanced concepts like recursion and anonymous functions.

Arrays are indispensable in PHP, providing a way to store and manipulate collections of data. You will explore different types of arrays, including indexed, associative, and multidimensional arrays, and learn how to perform common operations such as sorting, merging, and filtering.

Processing and validating user input through forms are essential skills for any web developer. This book covers form handling techniques, data validation, and security measures to protect against common vulnerabilities like SQL injection and cross-site scripting.

Database interaction is another core component of PHP, enabling the creation of dynamic and data-driven applications. You will learn how to connect to databases, execute queries, and manage data using PHP’s built-in functions and the PDO (PHP Data Objects) extension.

Object-oriented programming (OOP) is introduced to help you write modular and reusable code. Concepts like classes, objects, inheritance, and polymorphism will be explained, providing a solid foundation for building complex applications.

Finally, the book addresses error handling and debugging techniques, essential for developing robust and reliable applications. You will learn how to use PHP’s error handling functions and tools to identify and resolve issues in your code effectively.

By the end of this book, you will have gained a deep understanding of PHP and its application in web development, enabling you to build sophisticated, dynamic, and interactive websites.

Chapter 1

Introduction to PHP

PHP is a widely-used open-source server-side scripting language designed specifically for web development. This chapter explores the history and evolution of PHP, its installation process, and the setup of a local development environment. It introduces the basic syntax, including PHP tags, variables, constants, and the integration of PHP with HTML. Concepts like PHP comments and basic output methods are also discussed, providing a solid foundation for further learning in subsequent chapters.

1.1

History and Evolution of PHP

PHP, an acronym for Hypertext Preprocessor, was originally created in 1994 by Rasmus Lerdorf. Initially, it was a set of Common Gateway Interface (CGI) binaries written in the C programming language. This set of tools was known as PHP/FI (Personal Home Page/Form Interpreter). It enabled Rasmus to track visits to his online resume and incorporate some basic functionalities such as displaying dynamic content on web pages.

The significance of PHP/FI lay in its simplicity and its ability to closely integrate with HTML coding, allowing the generation of dynamic web content. The early adoption of PHP was spurred by its ease of use for web developers who were already familiar with C and Perl, and by its capability to rapidly deliver web applications compared to competitor technologies available at the time.

By mid-1997, PHP/FI 2.0 had become a tool used by approximately 50,000 domains. The demand for improved functionalities led to the expansion of PHP beyond a simple scripting language. Two key contributors, Zeev Suraski and Andi Gutmans, crafted the foundation for PHP 3.0. PHP 3.0 marked a pivotal point in the language’s evolution, officially released in June 1998. It featured a thorough overhaul of the parser and introduced a more extensible modular architecture that allowed developers to easily add their own functionality.

Following PHP 3.0, Suraski and Gutmans began a complete rewrite of the PHP’s core, producing the Zend Engine, named combining letters from their names. This rewrite led to PHP 4.0, released in May 2000, which came with key improvements in terms of performance, reliability, and scalability. PHP 4.0 implemented the Zend Engine 1.0, allowing advanced session handling, output buffering, and a more robust parsing mechanism which effectively increased the language’s popularity among developers for building dynamic websites.

In 2004, PHP 5.0 was introduced, fundamentally improving the language’s capabilities as an object-oriented programming (OOP) language. This version used the Zend Engine 2.0, which vastly improved support for object orientation, incorporating features such as interfaces, abstract classes, and the adoption of exceptions for error handling. Another major inclusion in PHP 5 was the PHP Data Objects (PDO) extension, a consistent interface for accessing databases. These advancements began to position PHP as not merely a scripting tool but a serious programming language for large-scale enterprise applications.

Subsequent minor versions, such as PHP 5.3, made significant strides by introducing lambda functions and closures, among other features. PHP 5.4 eased the hardware burden on web servers by reducing memory consumption and adding the built-in web server, aiding development processes by eliminating the complexity of configuring a separate server.

PHP 7.0, released in December 2015, brought about another monumental transformation. PHP 6, which aimed to integrate Unicode support directly into the core, was abandoned due to numerous complications and performance issues. Instead, PHP 7 introduced a highly optimized version using the new Zend Engine 3.0. Performance improvements enabled PHP 7 to execute tasks twice as fast as its predecessor. The language also introduced scalar type declarations, return type declarations, and a myriad of other features aimed at improving type safety and developer experience.

The constant improvements laid out in PHP 7 and the ongoing iterations, including PHP 7.1, 7.2, and beyond, focused on performance and language consistency. These steps exhibit a clear direction toward modernization and efficiency without sacrificing the simplicity and ease of use that fueled PHP’s initial growth.

In parallel to this, PHP 8.0, released in November 2020, took a large leap by introducing the Just-In-Time (JIT) compilation. This feature translated compiled code into machine code at runtime, drastically enhancing performance for tasks not necessarily tied to web development but that could benefit from optimization at the execution level. Enhancements like union types, attributes, constructor property promotion, and match expressions also diversified PHP’s capabilities.

Understanding PHP’s history and developments elucidates how the language has grown from its humble beginnings as a simple tool for personal web pages to a robust, high-performance language used in various contexts from small projects to enterprise-level applications. This gradual and meticulous evolution has been driven by PHP’s worldwide community, contributing to its steady refinement and expansion. This collaborative energy ensures that PHP remains relevant and responsive to the needs of a diverse user base.

1.2

What is PHP?

PHP, which stands for Hypertext Preprocessor, is a powerful language designed primarily for server-side web development. PHP scripts are executed on the server, and the result is transmitted to the client’s browser in HTML. Unlike traditional compiled languages, PHP is interpreted, meaning that the code is executed directly without compilation into machine language. This provides flexibility and ease of coding, allowing developers to write and test code rapidly.

PHP was created by Rasmus Lerdorf in 1994, initially as a collection of CGI scripts written in C to maintain his personal homepage. It has since evolved into a full-fledged programming language, with contributions from a vast community of developers. It is now a cornerstone of modern web development due to its versatility, efficiency, and extensive library of built-in functions.

PHP is designed to interact seamlessly with various database management systems, including MySQL, PostgreSQL, and SQLite, among others. This functionality makes PHP particularly suitable for creating dynamic web applications where content must change in response to user interactions. Integration with databases can be achieved through native functions or more abstracted methodologies such as PDO (PHP Data Objects).

The syntax of PHP borrows elements from C, Java, and Perl, making it familiar to a wide range of programmers. It supports common programming paradigms, including procedural, object-oriented, and functional programming techniques. This allows developers to choose the style that best suits their application requirements.

To provide practical understanding, consider the following PHP code snippet:

php

$greeting

=

"

Hello

,

World

!

"

;

echo

$greeting

;

?>

This script initializes the PHP variable $greeting with the string Hello, World! and then uses the echo statement to output this string to the browser. The tags indicate where the PHP code starts and ends, allowing it to be embedded within an HTML document seamlessly.

When we view the output of executing the above code in a web browser, we would see the following:

Hello, World!

PHP code is executed on the server, thus ensuring that the source code itself is not exposed to end users. Only the generated HTML is sent to the client’s browser, enhancing security and control over the application logic.

One of PHP’s strengths is its extensive array of built-in functions. These functions provide capabilities ranging from basic string and array manipulations to more complex operations such as cryptography and image processing. For example, the strlen function can be used to determine the length of a string:

php

$length

=

strlen

(

"

Hello

,

World

!

"

)

;

echo

$length

;

?>

The output from this code segment would be:

13

PHP’s agility is further enhanced through its error reporting functionality. Developers can control error reporting levels using the error_reporting function, making it easier to debug and develop robust applications.

Beyond procedural and functional programming, PHP also supports object-oriented programming (OOP), enabling developers to define classes and objects. This facilitates modular, reusable code and promotes code organization and maintainability. For instance:

php

class

Greeting

{

public

$message

;

function

__construct

(

$message

)

{

$this

->

message

=

$message

;

}

function

displayMessage

()

{

echo

$this

->

message

;

}

}

$greet

=

new

Greeting

(

"

Hello

,

Object

-

Oriented

World

!

"

)

;

$greet

->

displayMessage

()

;

?>

This script defines a Greeting class with a constructor and a method displayMessage. When instantiated, it stores the message and can output it using its method. The output would similarly be:

Hello, Object-Oriented World!

In PHP 7 and later versions, language performance and error handling have been significantly improved. PHP 7 introduced scalar type declarations and return type declarations, providing greater control over function behavior. Additionally, the introduction of anonymous classes allows for more concise and flexible coding.

Given PHP’s evolving nature, it is prudent for developers to remain abreast of new features and practices, leveraging PHP’s capabilities to build efficient, maintainable, and secure web applications.

1.3

Installing PHP

To begin utilizing PHP for web development, a proper and efficient installation of the PHP interpreter is paramount. This section outlines the necessary steps to install PHP on various operating systems, ensuring that the reader can seamlessly set up their development environment and commence scripts execution.

Prerequisites:

Before installing PHP, ensure that you have administrative access to your machine, as you will need it to install new software.

PHP Installation on Windows:

1. Download PHP: Visit the official PHP website (https://www.php.net/) and navigate to the Downloads section. Choose the Windows downloads, and download the latest Thread Safe version zip file.

2. Extract Files: Unzip the downloaded file into a directory of your choice, for example, C:\php.

3. Configure php.ini: Navigate to the extracted directory. Locate php.ini-development and rename it to php.ini. Edit php.ini with a text editor, removing the comment (semicolon) from the following lines:

extension_dir = ext

extension=curl

extension=pdo_mysql

4. Add PHP to System Path:

setx

PATH

"

%

PATH

%;

C

:\

php

"

This command ensures that PHP is accessible from the command line. Restart your computer to apply changes.

5. Verify Installation:

Open Command Prompt and type:

php

-

v

The command should display the installed PHP version.

PHP Installation on macOS:

1. Using Homebrew:

Homebrew is a popular package manager for macOS. First, install Homebrew by pasting the following command into Terminal:

/

bin

/

bash

-

c

"

$

(

curl

-

fsSL

https

://

raw

.

githubusercontent

.

com

/

Homebrew

/

install

/

HEAD

/

install

.

sh

)

"

Once Homebrew is installed, you can install PHP with:

brew

install

php

2. Verify Installation: Use the following command to check the installed PHP version:

php

-

v

The displayed version should confirm PHP’s successful installation.

PHP Installation on Linux:

1. Using Advanced Package Tool (APT) on Debian-based systems (e.g., Ubuntu):

sudo

apt

update

sudo

apt

install

php

libapache2

-

mod

-

php

This command will install PHP and its associated module for Apache.

2. Using YUM on Red Hat-based systems (e.g., CentOS, Fedora):

sudo

yum

install

php

It installs PHP on your system.

3. Verify Installation: Ensure PHP is installed correctly by typing:

php

-

v

The PHP version should be displayed, confirming the installation’s completion.

Configuring PHP:

After installation, some configurations may be necessary to tailor PHP behavior to your development needs. Open php.ini located in /etc (Linux/Mac) or the PHP installation directory (Windows) and adjust according to the following common settings:

Error Reporting:

error_reporting

=

E_ALL

display_errors

=

On

These settings will enable the display of all errors, which is useful during development stage.

Setting Timezone:

date

.

timezone

=

"

America

/

New_York

"

Adjust the timezone to match your local time.

Increasing Memory Limit:

memory_limit

=

256

M

This setting is particularly useful when working with large files or memory-intensive applications.

Finally, it is advisable to verify your web server is correctly interfaced with PHP. If using Apache, restart the server and create a test PHP file, info.php, in the document root with the following content:

php

phpinfo

()

;

?>

Access http://localhost/info.php in your web browser; you should see a page displaying detailed PHP configuration information. This indicates that PHP is successfully installed and configured.

Following these steps ensures that PHP is correctly installed and ready for development.

1.4

Setting Up a Local Development Environment

To effectively develop and test PHP scripts, setting up a local development environment is crucial. This section will guide you through the process of installing and configuring the essential components required to run PHP on your computer.

A typical local development environment includes the following components:

Web Server: Typically Apache or Nginx

PHP: The scripting language itself

Database: Commonly MySQL or MariaDB for storing data

Installing XAMPP

XAMPP is one of the most popular options for setting up a local development environment. It stands for Cross-Platform (X), Apache (A), MySQL (M), PHP (P), and Perl (P).

1. First, download XAMPP from the official website ( https://www.apachefriends.org/download.html ). Choose the version that matches your operating system (Windows, macOS, or Linux). 2. Once the download is complete, run the installer. Follow the installation wizard steps:

Select components: Ensure that Apache, MySQL, and PHP are selected.

Choose an installation directory: The default is usually acceptable.

Start the installation process and wait for it to complete.

3. After installation, launch the XAMPP Control Panel. You should see options to start/stop Apache and MySQL. 4. Start Apache and MySQL by clicking their respective Start buttons. 5. Verify the installation by opening a web browser and navigating to http://localhost. You should see the XAMPP dashboard.

Configuring PHP

Once XAMPP is installed and running, the next step involves configuring PHP to suit your development needs. Key configuration settings are found in the php.ini file.

1. Locate the php.ini file. It is usually found in the php directory within your XAMPP installation directory. 2. Open the php.ini file in a text editor with administrative privileges. 3. Adjust settings as needed:

display_errors = On: Useful during development to display error messages.

error_reporting = E_ALL: Ensure all types of errors are reported.

memory_limit = 256M: Allocate sufficient memory for running scripts.

upload_max_filesize = 64M: Set maximum file upload size.

4. Save the changes and restart Apache via the XAMPP Control Panel to apply the new settings.

Setting Up a Code Editor

A suitable code editor or Integrated Development Environment (IDE) enhances coding efficiency. Some widely-used PHP editors/IDEs include VS Code, PhpStorm, and Sublime Text.

1. Download and install your preferred code editor. For instance, you can download VS Code from https://code.visualstudio.com/ . 2. Install PHP-specific extensions or plugins for better syntax highlighting, code completion, and debugging support. For VS Code:

Open the Extensions view by clicking on the Extensions icon in the Activity Bar.

Search for and install extensions like PHP Intelephense, PHP Debug, and PHP IntelliSense.

3. Configure the editor settings to tailor the development experience to your preference.

Testing the Environment with a Simple PHP Script

To confirm that the environment is properly set up, create and run a basic PHP script.

1. Open your code editor and create a new file named test.php . 2. Enter the following PHP code:

php

echo

"

Hello

,

World

!

"

;

?>

3. Save the test.php file in the htdocs directory within your XAMPP installation directory. This is typically C:\xampp\htdocs on Windows or /Applications/XAMPP/htdocs on macOS. 4. Open a web browser and navigate to http://localhost/test.php. You should see the output:

        Hello, World!

This verifies that the local development environment is successfully configured and ready for PHP development. Adjust the configuration parameters and extensions based on your specific requirements to optimize your development process.

1.5

Your First PHP Script

Creating your first PHP script involves understanding the basic elements and structure of PHP. PHP scripts are typically embedded within HTML to enable dynamic content generation. PHP code is executed on the server and then sent to the client as plain HTML. Here, we will guide you through writing a simple PHP script to get you started.

To begin, ensure you have set up your local development environment as described in the previous sections. You should have a working web server (like Apache) and PHP installed. Additionally, use a text editor or an Integrated Development Environment (IDE) to write your PHP code.

PHP code is enclosed within PHP tags. The most common PHP tag is:

php

...

?>

Between these tags, you can write your PHP code. Let’s create a simple PHP script file named first_script.php.

php

//

This

is

your

first

PHP

script

echo

"

Hello

,

World

!

"

;

?>

Save this PHP script in your web server’s document root directory (e.g., C:/xampp/htdocs/ for XAMPP on Windows or /var/www/html/ for a typical Linux setup).

To run this PHP script, open your web browser and navigate to http://localhost/first_script.php. The server processes the PHP code and returns the following output:

Hello, World!

Let’s break down the script to understand each component:

: These are the PHP opening and closing tags. All PHP code must be written inside these tags.

// This is your first PHP script: This is a single-line comment in PHP. Comments are not executed by the server and are used to explain the code.

echo Hello, World!;: The echo statement is used to output text or variables to the web page. Here, it outputs the string Hello, World!.

You have successfully created and run your first PHP script. Next, we will enhance this script with some basic PHP functionality. Let’s add variables and arithmetic operations.

Open your first_script.php file and update it as follows:

php

//

This

is

your

first

PHP

script

with

variables

$greeting

=

"

Hello

,

World

!

"

;

$number1

=

10;

$number2

=

20;

$sum

=

$number1

+

$number2

;

echo

$greeting

;

echo

"

<

br

>

"

;

//

HTML

line

break

echo

"

The

sum

of

"

.

$number1

.

"

and

"

.

$number2

.

"

is

:

"

.

$sum

;

?>

After saving the file, refresh the browser to see the output:

Hello, World!

The sum of 10 and 20 is: 30

In this updated script:

$greeting, $number1, $number2, and $sum are variables.

Variables in PHP start with a dollar sign ($) followed by the variable name.

$greeting stores the string Hello, World!.

$number1 and $number2 store the integer values 10 and 20, respectively.

$sum stores the result of the arithmetic operation $number1 + $number2.

echo
;: Includes an HTML line break to separate the outputs.

echo The sum of . $number1 . and . $number2 . is: . $sum;: Concatenates and outputs a string with variable values. The dot (.) operator in PHP is used to concatenate strings.

Now, let’s incorporate some user inputs using URL parameters. Modify your code as follows:

php

//

First

PHP

script

with

user

input

$greeting

=

"

Hello

,

World

!

"

;

$number1

=

$_GET

[

’

num1

’

];

$number2

=

$_GET

[

’

num2

’

];

$sum

=

$number1

+

$number2

;

echo

$greeting

;

echo

"

<

br

>

"

;

//

HTML

line

break

echo

"

The

sum

of

"

.

$number1

.

"

and

"

.

$number2

.

"

is

:

"

.

$sum

;

?>

In this example:

$_GET[’num1’] and $_GET[’num2’] retrieve values from the URL parameters.

To test this script, navigate to: http://localhost/first_script.php?num1=10&num2=20

Output:

Hello, World!

The sum of 10 and 20 is: 30

Thus, you have learned how to create a basic PHP script, use variables, perform arithmetic operations, and incorporate user inputs. This lays the foundation for further exploration of PHP programming.

1.6

Basic Syntax of PHP

PHP, or Hypertext Preprocessor, is a versatile scripting language that is predominantly embedded within HTML. As we delve into the basic syntax of PHP, it is imperative to understand how PHP code is enclosed, structured, and executed within the server environment. Below, we explore fundamental elements such as PHP tags, statements, and common syntactic conventions which establish the baseline for writing effective PHP scripts.

PHP code is typically enclosed within special opening and closing tags that allow the PHP interpreter to differentiate between PHP code and other markup such as HTML. The standard form of these tags is:

php

//

PHP

code

goes

here

?>

The tag marks its end. It is essential to correctly enclose all PHP scripts within these tags to ensure proper interpretation and execution by the server.

A PHP script is composed of a series of statements, typically ending with a semicolon. Statements may include variable declarations, assignments, function calls, and control structures. For example:

php

echo

"

Hello

,

world

!

"

;

?>

In this script, echo outputs the string Hello, world! to the web page, and the statement terminates with a semicolon.

Variables in PHP are declared with the dollar sign ($) followed by a variable name. Variable names must begin with a letter or an underscore, followed by any number of letters, numbers, or underscores. PHP is a dynamically typed language, so variable types do not need to be explicitly declared. Here is an example of variable declaration and assignment:

php

$username

=

"

john_doe

"

;

$age

=

21;

$balance

=

100.50;

?>

PHP supports several data types including strings, integers, floats, booleans, arrays, objects, and more. Variables can be reassigned values of different types over their lifespan within a script, underscoring the language’s dynamic nature.

php

$variable

=

"

Hello

,

world

!

"

;

//

string

$variable

=

100;

//

integer

$variable

=

75.5;

//

float

$variable

=

true

;

//

boolean

?>

Constants in PHP are defined using the define() function and cannot be changed after they have been set. Constants are useful for defining values that remain constant throughout the execution of a script.

php

define

(

"

SITE_URL

"

,

"

https

://

www

.

example

.

com

"

)

;

echo

SITE_URL

;

//

Outputs

:

https

://

www

.

example

.

com

?>

Control structures are essential in PHP for directing the flow of execution based on certain conditions. The most common control structures include if-else statements, loops (for, while, foreach), and switch statements. Here is an example of an if-else statement:

php

$number

=

10;

if

(

$number

>

0)

{

echo

"

The

number

is

positive

.

"

;

}

elseif

(

$number

<

0)

{

echo

"

The

number

is

negative

.

"

;

}

else

{

echo

"

The

number

is

zero

.

"

;

}

?>

Indentation and proper spacing enhance readability but are not syntactically