PHP Development Lecture Notes

Server-side Development with PHP

Introduction to PHP

  • PHP is a server-side scripting language specifically designed for the web.

  • It allows for embedding PHP code within an HTML page.

  • PHP code is executed at the web server, generating HTML or other output for the visitor to see.

Origin of PHP

  • Originally stood for Personal Home Page.

  • Name changed according to the GNU recursive naming convention, now stands for PHP Hypertext Preprocessor.

Strengths of PHP

Main Competitors

  • Major competitors include:

    • Python

    • Ruby (including Ruby on Rails)

    • Node.js

    • Perl

    • Microsoft .NET

    • Java

Key Strengths

  • Performance: Efficient processing of scripts.

  • Scalability: Suitable for growth as demands increase.

  • Database Interfaces: Supports many different database systems.

  • Built-in Libraries: Offers many libraries for common web tasks.

  • Low Cost: Generally cost-effective to use.

  • Ease of Learning: User-friendly syntax conducive to beginners.

  • Object-Oriented Support: Strong support for object-oriented programming concepts.

  • Portability: Runs on various platforms with little modification.

  • Development Flexibility: Offers a variety of approaches to development.

  • Source Code Availability: Open-source nature allows for modification and distribution.

  • Support and Documentation: Extensive support and resources are available.

Incorporating PHP within HTML

File Extension

  • PHP documents typically end with the .php extension.

  • Web servers recognize this extension and automatically pass it to the PHP processor.

Configuration Options

  • Developers can configure web servers to process files with .htm or .html extensions through the PHP processor to hide the use of PHP.

Basic PHP Document Structure

  • A basic PHP document that outputs only HTML might look as follows:

  <?php
  // your PHP code here
  ?>

  • An existing HTML file (e.g., index.html) can be renamed to index.php and it will display identically but can also incorporate PHP.

PHP Command Syntax

  • PHP commands are defined within tags starting with and ending with ?>.

Using Comments in PHP

Single-line Comments

  • Use // to comment a single line.

Multi-line Comments

  • Use / and */ for comments across multiple lines:

  /* This is a
  multi-line comment */

Error Handling

  • A common error in PHP is forgetting to end commands with a ; (semicolon), leading to a Parse error because PHP treats multiple statements as a single statement.

Variables in PHP

Variable Declaration

  • All variables in PHP must start with a $ sign (e.g., $variable).

  • This convention helps the PHP parser identify variables quickly.

Super Global Variables

Definition

  • Super global variables are predefined variables accessible across all scopes within PHP.

Common Super Global Variables

  1. SERVER:Holdsinformationaboutheaders,paths,andscriptlocations.</strong></p></li><li><p><strong>_SERVER: Holds information about headers, paths, and script locations.</strong></p></li><li><p><strong>_POST: Collects data from an HTML form after submission.

  2. GET:CollectsdatafromformsviaURLparametersordirectURLinput.</strong></p></li><li><p><strong>_GET: Collects data from forms via URL parameters or direct URL input.</strong></p></li><li><p><strong>_FILES: A multidimensional array containing information about uploaded files.

  3. $_SESSION: Stores session data that persists during a user's session.

Arrays in PHP

Basic Definition

  • An array stores multiple values in a single variable.

Indexed Arrays

  • Arrays can have numeric indices. Example:

  $paper[] = "Copier";
  $paper[] = "Inkjet";

  • Output example:

  Array(
  [0] => "Copier"
  [1] => "Inkjet"
  ...
  )

Two-dimensional and Multi-dimensional Arrays

Definition

  • A two-dimensional array is defined as an array of arrays; a three-dimensional array is an array of arrays of arrays.

Example

  • A tic-tac-toe game uses a structure of nine cells arranged in a 3x3 format.

Associative Arrays

Definition

  • An associative array allows elements to be referenced by names instead of indices:

  $paper['copier'] = "Copier & Multipurpose";

Operators in PHP

Arithmetic Operators

  • Common operators include:

    • +: Addition

    • -: Subtraction

    • **
      **: Multiplication

    • /: Division

    • %: Modulus

Assignment Operators

  • Examples include:

    • =: Simple assignment

    • +=: Adds and assigns ($j += 5 is equivalent to $j = $j + 5)

    • -=: Subtracts and assigns

Comparison Operators

  • Used for comparing two values. Examples include:

    • ==: Equal to

    • !=: Not equal to

    • >: Greater than

    • <: Less than

    • >=: Greater than or equal to

    • <=: Less than or equal to

Logical Operators

  • Combine conditional statements using:

    • &&: And

    • ||: Or

    • !: Not

Conditional Statements

If Statement

  • The structure can evaluate any PHP expression, such as equality and comparison.

Else Statement

  • Provides alternative code to execute when the if condition is not TRUE.

Elseif Statement

  • Allows for multiple conditions using elseif for a sequence of possibilities.

Switch Statement

  • Useful for scenarios where a variable might have multiple potential values, each triggering distinct actions.

Loops in PHP

Purpose

  • Loops are used to repeat a sequence of code until a certain condition is met (e.g., user input).

Loop Types

  1. While loop: Continues as long as a condition is TRUE.

  2. Do while loop: Executes at least once before checking the condition.

  3. For loop: Generally used for iterating a specific number of times.

  4. Foreach … as loop: Specialized for iterating over arrays.

Functions in PHP

Built-in Functions

  • PHP offers many built-in functions for various operations.

Defining a Function

  • Function names are case-insensitive.

  • A function's structure includes:

  function functionName() {
      // code to execute
  }

  • Each function can include one or more return statements to send values back to the caller.

Including and Requiring Files

Purpose

  • Facilitates code organization; reuse functions without duplicating code.

Commands

  1. include: Pulls in the contents of a file.

  2. include_once: Ensures that a file is included only once during the execution.

  3. require: Similar to include, but halts execution if the file is not found.

  4. require_once: Like require but done only once, ensuring the code is not added multiple times.