PHP

PHP is an open source server-side scripting language designed for Web development to produce dynamic Web pages. It is one of the first developed server-side scripting languages to be embedded into an HTML source document rather than calling an external file to process data. The code is interpreted by a Web server with a PHP processor module which generates the resulting Web page. It also has evolved to include a command-line interface capability and can be used in standalone graphical applications.  A competitor to Microsoft's Active Server Pages (ASP) server-side script engine and similar languages, PHP is installed on more than 20 million Web sites and 1 million Web servers Notable software that uses PHP includes 

Definition: The echo () function is used to output the given argument. It can output all types of data and multiple outputs can be made with only one echo () command.

Examples:

 Echo "Hello";

 //Outputs a string

 Echo $variable;

 //Outputs a variable

 Echo "Multiple things " . $on . " one line";

 //Outputs a string, then a variable, then a string. All are separated with a [.] period

 ?>

What You Should Already Know

Before you continue you should have a basic understanding of the following:

•     HTML
•     JavaScrip

PHP Means

•  PHP stands for PHP: Hypertext Preprocessor
• PHP is a widely-used, open source scripting language
• PHP scripts are executed on the server
• PHP is free to download and use

PHP File

• PHP files can contain text, HTML, JavaScript code, and PHP code
• PHP code are executed on the server, and the result is returned to the browser as plain HTML
• PHP files have a default file extension of ".php"

PHP Can Do

• PHP can generate dynamic page content
• PHP can create, open, read, write, and close files on the server
• PHP can collect form data
• PHP can send and receive cookies
• PHP can add, delete, modify data in your database
• PHP can restrict users to access some pages on your website
• PHP can encrypt data

With PHP you are not limited to output HTML. You can output images, PDF files, and even Flash movies. You can also output any text, such as XHTML and XML

PHP Uses

• PHP runs on different platforms (Windows, Linux, Unix, Mac OS X, etc.)
• PHP is compatible with almost all servers used today (Apache, IIS, etc.)
• PHP has support for a wide range of databases

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PHP Syntax

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

On servers with shorthand-support, you can start a PHP script with .

For maximum compatibility, we recommend that you use the standard form (

// PHP code goes here
?>

The default file extension for PHP files is ".php".

A PHP file normally contains HTML tags, and some PHP scripting code.

Below, we have an example of a simple PHP script that sends the text "Hello World!" back to the browser:

Example

echo "Hello World!";
?>

Algebra x=5, y=6, z=x+y

These letters are called variables, and variables can be used to hold values (x=5) or expressions (z=x+y).

PHP Variables

A variable can have a short name, like x, or a more descriptive name, like carName.

Rules for PHP variable

•      Variables in PHP starts with a $ sign, followed by the name of the variable
•       The variable name must begin with a letter or the underscore character
•      A variable name can only contain alpha-numeric characters and underscores (A-z, 0-9, and _ )
•      A variable name should not contain spaces
•      Variable names are case sensitive (y and Y are two different variables)

Creating (Declaring) PHP

PHP has no command for declaring a variable.

A variable is created the moment you first assign a value to it:

$myCar="Volvo";

After the execution of the statement above, the variable myCar will hold the value Volvo.

Tip: If you want to create a variable without assigning it a value, then you assign it the value ofnull.

Let's create a variable containing a string, and a variable containing a number:

$txt="Hello World!";
$x=16;
?>

PHP is a Loosely Typed Language

In PHP, a variable does not need to be declared before adding a value to it.

In the example above, notice that we did not have to tell PHP which data type the variable is.

PHP automatically converts the variable to the correct data type, depending on its value.

In a strongly typed programming language, you have to declare (define) the type and name of the variable before using it.

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PHP Variable Scope

•        local
•        global
•        static
•        parameter

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Local Scope

A variable declared within a PHP function is local and can only be accessed within that function. (the variable has local scope):

$a = 5; // global scope

function myTest()
{
echo $a; // local scope
} 

myTest();
?>

The script above will not produce any output because the echo statement refers to the local scope variable $a, which has not been assigned a value within this 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.

Local variables are deleted as soon as the function is completed.

Global Scope

Global scope refers to any variable that is defined outside of any function.

Global variables can be accessed from any part of the script that is not inside a function.

To access a global variable from within a function, use the global keyword:

$a = 5;
$b = 10;

function myTest()
{
global $a, $b;
$b = $a + $b;
} 

myTest();
echo $b;
?>

The script above will output 15.

PHP also stores all global variables in an array called $GLOBALS[index]. Its index is 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 as this:

$a = 5;
$b = 10;

function myTest()
{
$GLOBALS['b'] = $GLOBALS['a'] + $GLOBALS['b'];
} 

myTest();
echo $b;
?>

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Setatic Scop

When a function is completed, all of its variables are normally deleted. However, sometimes you want a local variable to not be deleted.

To do this, use the static keyword when you first declare the variable:

static $rememberMe;

Then, each time the function is called, that variable will still have the information it contained from the last time the function was called.

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Parameters

 parameter is a local variable whose value is passed to the function by the calling code.

Parameters are declared in a parameter list as part of the function declaration:

function myTest($para1,$para2,...)
{
// function code
}

Parameters are alAso called arguments. We will discuss them in more detail when we talk about functions.