Introduction to PHP

• Server-side scripts offer a user interface and restrict access to proprietary data.
• Languages like ActiveVFP, ASP, C, Java, JavaScript, Perl, PHP, Python, and Ruby can create these scripts.
• Server-side scripts function on the web server via HTTP requests from the client.
• A client running a web browser sends an HTTP page request to the server, and the server responds with the requested page.

What is PHP?

• PHP stands for Hypertext Preprocessor (recursive acronym).
• PHP is an open-source, general-purpose scripting language.
• PHP is well-suited for web development and can be embedded into HTML.
• PHP simplifies scripting using databases and enforces platform independence.
• PHP is designed and optimized for web applications, response times, and it is open source.

PHP Requirements

• A web server and PHP engine are required.
• A Database server is needed if the application uses a database.
• A command line tool is needed for running PHP commands from the command line.
• XAMPP is used in this course.

Application Needs for PHP

• XAMPP with PHP version 8.x is required.
• Integrated Development Environment (IDE) needs to be used.

PHP Syntax

• PHP code blocks are embedded within <?php and ?> tags.
• When the server encounters PHP tags, it switches from HTML to PHP mode.
• <?php is the opening tag.
• ?> is the closing tag.

PHP Display

• The PHP echo Statement can be used with or without parentheses, for example: echo or echo().
• The PHP print Statement can be used with or without parentheses, for example: print or print().
• The print_r() function prints information about a variable in a more human-readable way.

Creating PHP File

• PHP files have a .php extension.
• PHP files should be stored in the XAMPP root folder, specifically in the "htdocs" folder.

Running PHP

• Open the XAMPP Control Panel.
• Start the virtual web server (Apache).
• Open a web browser.
• Access the URL using http://localhost/<folder name> or http://127.0.0.1/<folder name>.
• All PHP output is technically in HTML.
• PHP code can be placed anywhere within the HTML structure.
• It is important that the HTML structure is present when running PHP in a browser.

Comments

• Use // for single-line comments.
• Use # for single-line comments.
• Use /* */ for multi-line comments.

Variables

• Variables in PHP are represented by a dollar sign followed by the variable name, for example: $variable.
• Variable names are case-sensitive.

Operator Precedence

• Operator precedence specifies how "tightly" an operator binds to expressions.
• In 1 + 5 * 3, the answer is 16, because the multiplication operator has a higher precedence than the addition operator.
• Parentheses are used to force precedence; for example: (1 + 5) * 3 evaluates to 18.

Arithmetic Operators

• $a + $b: Addition to sum $a and $b.
• $a - $b: Subtraction to find the difference between $a and $b.
• $a * $b: Multiplication to find the product of $a and $b.
• $a / $b: Division to find the quotient of $a and $b.
• $a % $b: Modulus to find the remainder of $a divided by $b.
• $a ** $b: Exponentiation to raise $a to the power of $b.

Increment/Decrement Operators

• ++$a (Pre-increment): Increments $a by one, then returns $a.
• $a++ (Post-increment): Returns $a, then increments $a by one.
• --$a (Pre-decrement): Decrements $a by one, then returns $a.
• $a-- (Post-decrement): Returns $a, then decrements $a by one.

Comparison Operators

• $a == $b (Equal): Returns true if $a is equal to $b after type juggling.
• $a === $b (Identical): Returns true if $a is equal to $b, and they are of the same type.
• $a != $b (Not equal): Returns true if $a is not equal to $b after type juggling.
• $a <> $b (Not equal): Returns true if $a is not equal to $b after type juggling.
• $a !== $b (Not identical): Returns true if $a is not equal to $b, or they are not of the same type.
• $a < $b (Less than): Returns true if $a is strictly less than $b.
• $a > $b (Greater than): Returns true if $a is strictly greater than $b.
• $a <= $b (Less than or equal to): Returns true if $a is less than or equal to $b.
• $a >= $b (Greater than or equal to): Returns true if $a is greater than or equal to $b.
• $a <=> $b (Spaceship): An integer less than, equal to, or greater than zero when $a is less than, equal to, or greater than $b, respectively.

Logical Operators

• $a and $b (And): Returns true if both $a and $b are true.
• $a or $b (Or): Returns true if either $a or $b is true.
• $a xor $b (Xor): Returns true if either $a or $b is true, but not both.
• !$a (Not): Returns true if $a is not true.
• $a && $b (And): Returns true if both $a and $b are true.
• $a || $b (Or): Returns true if either $a or $b is true.

String Operators

• $a . $b (Concatenation): Returns the concatenation of its right and left arguments.
• $a .= $b (Concatenating assignment operator): Appends the argument on the right side to the argument on the left side.

Conditional Statements: IF Statement

• Executes code if a condition is true.

IF...Else Statement

• Executes code if a condition is true and another code block if that condition is false.

Nested IF Statement

• Involves inserting a second if statement inside another if statement.

Laddered IF Statement

• Executes different codes for more than two conditions.

Switch Statement

• Performs different actions based on different conditions and selects one of many code blocks to be executed.

While Loop

• Loops through a block of code as long as the specified condition is true.

Do...While Loop

• Loops through a block of code once, and then repeats the loop as long as the specified condition is true.

For Loop

• Loops through a block of code a specified number of times, controlled by an initial declaration, condition evaluation, and increment.

Foreach Loop

• Loops through a block of code for each element in an array and works only on arrays, it is used to loop through each key/value pair in an array.

Arrays

• An array in PHP is an ordered map optimized for several uses.
• Arrays can be treated as a list , hash table, dictionary, collection, stack, and queue.
• Array values can be other arrays, trees, and multidimensional arrays.
• A short array exists which replaces the array() function with [].

User-defined functions

• The syntax to define functions is shown in the examples.

GET Method

• GET is used to request data from a specified resource.
• The query string (name/value pairs) is sent in the URL of the GET request.
• GET requests can be cached and bookmarked.
• GET requests remain in the browser history.
• GET requests should never be used when dealing with sensitive data.
• GET requests have length restrictions, and are only used to request but not modify data.

POST Method

• POST is used to send data to a server to create/update a resource.
• The data sent is stored in the request body of the HTTP request.
• POST requests are never cached or bookmarked.
• POST requests do not remain in the browser history.
• POST requests have no restrictions on data length.

Compare GET vs. POST

• GET requests are harmless when using the back button/reload, but POST will re-submit an alert
• GET requests can be bookmarked, while POST requests cannot
• GET requests can be cached, POST requests cannot
• GET encoding type is application/x-www-form-urlencoded, POST requests are application/x-www-form-urlencoded or multipart/form-data, use multipart encoding for binary data
• GET parameters remain in-browser, POST parameters are no saved
• GET requests have restrictions on data length, POST do not
• GET requests are limited to ASCII, POST requests do not
• GET is less secure because data is part of the URL, POST is safer
• Use GET requests to send passwords, POST is displayed in the URL