Week 4 Topic 1: PHP basics

PHP Basics

• PHP (Hypertext Preprocessor) is a server-side scripting language essential for web development.
• Web developers use PHP to create dynamic content by embedding code within HTML.
• PHP facilitates communication between a website's front end and back end.
• PHP gives websites a dynamic edge, executing scripts on the server before rendering content.
• Dynamic web pages change content based on external inputs such as user searches.
• Two types of web programming languages exist: client-side and server-side.

Client-Side Programming

• Client-side programming executes inside the browser to change content.
• JavaScript is used to change content without reloading the page.
• HTML and CSS cannot generally create dynamic webpages

Server-Side Programming

• Server-side programming executes on the web server; results are sent to the web browser.
• Languages include PHP, NodeJS (JavaScript), Python, and TomCat (Java).
• Server-side code is never visible to the browser as it executes on the server.

Using PHP

• PHP is a server-side language that requires the server to be configured to run PHP.
• PHP's primary task is to generate HTML but can also generate other file types like images.
• With server support, PHP functions by creating .php files in the web directory.
• If the server doesn't support PHP, installation of a web server, PHP, and databases (e.g., MySQL) is required.
• PHP files can be opened with any text editor
• PHP filenames must end with .php to trigger execution by the PHP interpreter.
• PHP can be integrated directly into HTML code.
• signals the start of PHP code, and ends it.
• The echo keyword outputs a value to the browser.
• The time() function returns the time in seconds since the Unix Epoch.
• PHP statements end with a semicolon.
• When requested, PHP code executes on the server, sending HTML output to the browser.

Comments in PHP

• PHP comments provide information or disable code execution.
• // and # are for single-line comments; `` is for multi-line comments.

Variables

• PHP variables are containers for storing information
• Data types are automatically assigned to variables.
• Variable names start with a $.
• Variable names must start with a letter or underscore.
• They cannot start with a number and can only contain alphanumeric characters and underscores.
• Variable names are case-sensitive ($age and $AGE are different variables).
• Strings must be enclosed in quotes; other data types do not need them.
• Variables can store different types of data.

Functions

• PHP functions perform specific tasks and can take inputs (arguments).
• Functions can return a value or display results directly to the browser.
• PHP has over 1,000 built-in functions that can be called directly.
• In addition to built-in functions, custom functions can be created.
• Functions are blocks of code that can be used repeatedly.
• They will execute only when the function is called.

Function Arguments

• Information can be passed to PHP functions through arguments specified inside parentheses.
• Multiple arguments can be added, separated by commas.

Returning Functions

• The return statement is used to return a value from a function.
• The dot (.) operator is used to concatenate strings (e.g., "echo 1 . 2" prints "12").

The var_dump Function

• The var_dump() function outputs a variable's value and data type.
• The function is useful for identifying a variable's data type or value.
• For strings, the length of the string is also displayed in the output.

Echo and Print

• echo and print produce output in PHP, with echo being more commonly used due to its speed and flexibility.
• When combined with conditions, they can ensure the desired data is outputted.

PHP Constants

• A constant is an identifier for a simple value that cannot be changed during the script.
• The define() function creates a constant.
• define(name, value, case-insensitive) defines the constant's name, value, and case sensitivity.
• Case-insensitive defaults to false.

The Equal Operator

• The equal operator (==) checks that the values match.
• The triple equal operator (===) checks that the values and data types match.
• PHP automatically converts data types as required when using ==.

If...Else Statement

• PHP supports if statements similarly to other programming languages.

Elseif Statement

• The elseif statement allows for more than two outcomes in an if statement.
• Multiple elseif statements can be used; else is optional but must be at the end.

Combining Conditions

• Logical operators allow the combination and evaluation of conditions.

Logical Operators

• and / && : True if both $x and $y are true
• or / || : True if either $x or $y is true
• xor : True if either $x or $y is true, but not both
• ! : True if $x is false

Loops

• Loops allow you to repeat a block of code multiple times, useful for iterating over data structures.

Joining Strings

• Strings can be joined using + (adds data types together) or . (concatenates data types).
• When adding, PHP converts the string to an integer value and adds it
• When concatenating the string is untouched and joined directly

PHP Quotes

• PHP allows the use of double quotes ("a") or single quotes ('a') for strings.
• Double quotes convert escape sequences and replace variables with their values.
• Double quotes generally preferred due to their functionality.

Creating an Array in PHP

• The array() function is used to create arrays in PHP.

Indexed Arrays

• Indexed arrays assign each element a numeric index.
• Indexes can be assigned automatically (starting at 0) or manually.

Associative Arrays

• Associative arrays use named keys (strings).

Multidimensional Arrays

• Multidimensional arrays contain one or more arrays and can have multiple levels.