4. PHP Syntax and PHP Variables

The PHP linguistic structure and semantics are the organization (punctuation) and the related implications (semantics) of the content and images in the PHP programming language. They structure a lot of decides that characterize how a PHP program can be composed and deciphered.
PHP for the most part pursues C punctuation, with exemptions and improvements for its fundamental use in web advancement, which utilizes string control. PHP factors must be prefixed by “$”. This permits PHP to perform string interjection in twofold cited strings, where oblique punctuation line is upheld as a getaway character. No getting away or interjection is done on strings delimited by single statements. PHP likewise underpins a C-like sprintf work. Code can be modularized into capacities characterized with catchphrase work. PHP bolsters a discretionary article arranged coding style, with classes meant by the class catchphrase. Capacities characterized inside classes are some of the time called strategies. Control structures include: if, while, do/while, for, foreach, and switch. Explanations are ended by a semicolon, not line endings.

PHP Syntax

A PHP content is executed on the server, and the plain HTML result is sent back to the program.

Basic PHP Syntax

A PHP script can be placed anywhere in the document.
A PHP script starts with  <?php and ends with ?>:

The default record augmentation for PHP documents is “.php”.
A PHP record ordinarily contains HTML labels, and some PHP scripting code.
Beneath, we have a case of a basic PHP record, with a PHP content that uses an inherent PHP function “echo” to yield the content “Hi World!” on a website page. Example :

Note: PHP statements end with a semicolon (;).

PHP Case Sensitivity

In PHP, NO keywords (e.g. if, else, while, echo, etc.), classes, functions, and user-defined functions are case-sensitive.
In the example below, all three echo statements below are equal and legal:

Note: However; all variable names are case-sensitive!
Look at the example below; only the first statement will display the value of the $color variable! This is because $color, $COLOR, and $coLOR are treated as three different variables:

PHP Comments

Comments in PHP

A comment in PHP code is a line that is not executed as a part of the program. Its only purpose is to be read by someone who is looking at the code.
Comments can be used to:

• Let others understand your code
• Remind yourself of what you did – Most programmers have experienced coming back to their own work a year or two later and having to re-figure out what they did. Comments can remind you of what you were thinking when you wrote the code

PHP supports several ways of commenting:

Example syntax for single-line comments

Example syntax for multiple-line comments

Example using comments to leave out parts of the code

PHP Variables

Variables are “containers” for storing information.
Creating (Declaring) PHP Variables
In PHP, a variable starts with the $ sign, followed by the name of the variable:

After the execution of the statements above, the variable $txt will hold the value Hello world!, the variable $x will hold the value 5, and the variable $y will hold the value 10.5.
Note: When you assign a text value to a variable, put quotes around the value.
Note: Unlike other programming languages, PHP has no command for declaring a variable. It is created the moment you first assign a value to it.

Think of variables as containers for storing data.

PHP Variables

A variable can have a short name (like x and y) or a more descriptive name (age, carname, total_volume).
Rules for PHP variables:

• A variable starts with the $ sign, followed by the name of the variable
• A variable name must start with a letter or the underscore character
• A variable name cannot start with a number
• A variable name can only contain alpha-numeric characters and underscores (A-z, 0-9, and _ )
• Variable names are case-sensitive ($age and $AGE are two different variables)

Remember that PHP variable names are case-sensitive!

Output Variables

The PHP echo statement is often used to output data to the screen.
The following example will show how to output text and a variable:

The following example will produce the same output as the example above:

The following example will output the sum of two variables:

Note: You will learn more about the echo statement and how to output data to the screen in the next chapter.

PHP is a Loosely Typed Language

In the example above, notice that we did not have to tell PHP which data type the variable is.
PHP automatically associates a data type to the variable, depending on its value. Since the data types are not set in a strict sense, you can do things like adding a string to an integer without causing an error.
In PHP 7, type declarations were added. This gives an option to specify the data type expected when declaring a function, and by enabling the strict requirement, it will throw a “Fatal Error” on a type mismatch.
You will learn more about strict and non-strict requirements, and data type declarations in the PHP Functions chapter.

PHP Variables Scope

In PHP, variables can be declared anywhere in the script.
The scope of a variable is the part of the script where the variable can be referenced/used.
PHP has three different variable scopes:

1. local
2. global
3. static

Global and Local Scope

A variable declared outside a function has a GLOBAL SCOPE and can only be accessed outside a function:
Example Variable with global scope:

A variable declared within a function has a LOCAL SCOPE and can only be accessed within that function:
Example variable with local scope:

You can have local variables with the same name in different functions, because local variables are only recognized by the function in which they are declared.

PHP The global Keyword

The global keyword is used to access a global variable from within a function.
To do this, use the global keyword before the variables (inside the function):

PHP also stores all global variables in an array called $GLOBALS[index]. The index holds the name of the variable. This array is also accessible from within functions and can be used to update global variables directly.
The example above can be rewritten like this:

PHP The static Keyword

Normally, when a function is completed/executed, all of its variables are deleted. However, sometimes we want a local variable NOT to be deleted. We need it for a further job.
To do this, use the static keyword when you first declare the variable: