PHP introduction


PHP is a server-side scripting language.

What You Should Already Know

Before you continue you should have a basic understanding of the following:
  • HTML/XHTML
  • JavaScript
If you want to study these subjects first, find the tutorials on our Home page.

What is PHP?

  • PHP stands for PHP: Hypertext Preprocessor
  • PHP is a server-side scripting language, like ASP
  • PHP scripts are executed on the server
  • PHP supports many databases (MySQL, Informix, Oracle, Sybase, Solid, PostgreSQL, Generic ODBC, etc.)
  • PHP is an open source software
  • PHP is free to download and use

What is a PHP File?

  • PHP files can contain text, HTML tags and scripts
  • PHP files are returned to the browser as plain HTML 
  • PHP files have a file extension of ".php", ".php3", or ".phtml"

What is MySQL?

  • MySQL is a database server
  • MySQL is ideal for both small and large applications
  • MySQL supports standard SQL
  • MySQL compiles on a number of platforms
  • MySQL is free to download and use

PHP + MySQL

  • PHP combined with MySQL are cross-platform (you can develop in Windows and serve on a Unix platform)

Why PHP?

  • PHP runs on different platforms (Windows, Linux, Unix, etc.)
  • PHP is compatible with almost all servers used today (Apache, IIS, etc.)
  • PHP is FREE to download from the official PHP resource: www.php.net
  • PHP is easy to learn and runs efficiently on the server side

Where to Start?

To get access to a web server with PHP support, you can:
  • Install Apache (or IIS) on your own server, install PHP, and MySQL
  • Or find a web hosting plan with PHP and MySQL support

What do you Need?

If your server supports PHP you don't need to do anything.
Just create some .php files in your web directory, and the server will parse them for you. Because it is free, most web hosts offer PHP support.
However, if your server does not support PHP, you must install PHP.
Here is a link to a good tutorial from PHP.net on how to install PHP5:http://www.php.net/manual/en/install.php

Download PHP

Download PHP for free here: http://www.php.net/downloads.php

Download MySQL Database

Download MySQL for free here: http://www.mysql.com/downloads/

Download Apache Server

Download Apache for free here: http://httpd.apache.org/download.cgi
The PHP script is executed on the server, and the plain HTML result is sent back to the browser.

Basic PHP Syntax

A PHP script always starts with <?php 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 <? and end with ?>.
For maximum compatibility, we recommend that you use the standard form (<?php) rather than the shorthand form.
<?php
?>
A PHP file must have a .php extension.
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:
<html>
<body>

<?php
echo "Hello World";
?>

</body>
</html>
Each code line in PHP must end with a semicolon. The semicolon is a separator and is used to distinguish one set of instructions from another.
There are two basic statements to output text with PHP: echo and print.
In the example above we have used the echo statement to output the text "Hello World".

Comments in PHP

In PHP, we use // to make a one-line comment or /* and */ to make a comment block:
<html>
<body>

<?php
//This is a comment

/*
This is
a comment
block
*/
?>

</body>
</html>

Do You Remember Algebra From School?

Do you remember algebra from school? x=5, y=6, z=x+y
Do you remember that a letter (like x) could be used to hold a value (like 5), and that you could use the information above to calculate the value of z to be 11?
These letters are called variables, and variables can be used to hold values (x=5) or expressions (z=x+y).

PHP Variables

As with algebra, PHP variables are used to hold values or expressions.
A variable can have a short name, like x, or a more descriptive name, like carName.
Rules for PHP variable names:
  • 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 Variables

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:
<?php
$txt="Hello World!";
$x=16;
?>
Note: When you assign a text value to a variable, put quotes around the value.

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.

PHP Variable Scope

The scope of a variable is the portion of the script in which the variable can be referenced.
PHP has four different variable scopes:
  • local
  • global
  • static
  • parameter

Local Scope

A variable declared within a PHP function is local and can only be accessed within that function. (the variable has local scope):
<?php
$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:
<?php
$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:
<?php
$a = 5;
$b = 10;

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

myTest();
echo $b;
?>

Static Scope

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.
Note: The variable is still local to the function.

Parameters

A 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 also called arguments. We will discuss them in more detail when we talk about functions.

String Variables in PHP

String variables are used for values that contain characters.
In this chapter we are going to look at the most common functions and operators used to manipulate strings in PHP.
After we create a string we can manipulate it. A string can be used directly in a function or it can be stored in a variable.
Below, the PHP script assigns the text "Hello World" to a string variable called $txt:
<?php
$txt="Hello World";
echo $txt;
?>
The output of the code above will be:
Hello World
Now, lets try to use some different functions and operators to manipulate the string.

The Concatenation Operator

There is only one string operator in PHP.
The concatenation operator (.)  is used to put two string values together.
To concatenate two string variables together, use the concatenation operator:
<?php
$txt1="Hello World!";
$txt2="What a nice day!";
echo $txt1 . " " . $txt2;
?>
The output of the code above will be:
Hello World! What a nice day!
If we look at the code above you see that we used the concatenation operator two times. This is because we had to insert a third string (a space character), to separate the two strings.

The strlen() function

The strlen() function is used to return the length of a string.
Let's find the length of a string:
<?php
echo strlen("Hello world!");
?>
The output of the code above will be:
12
The length of a string is often used in loops or other functions, when it is important to know when the string ends. (i.e. in a loop, we would want to stop the loop after the last character in the string).

The strpos() function

The strpos() function is used to search for a character/text within a string.
If a match is found, this function will return the character position of the first match. If no match is found, it will return FALSE.
Let's see if we can find the string "world" in our string:
<?php
echo strpos("Hello world!","world");
?>
The output of the code above will be:
6
The position of the string "world" in the example above is 6. The reason that it is 6 (and not 7), is that the first character position in the string is 0, and not 1.

Complete PHP String Reference

For a complete reference of all string functions, go to our complete PHP String Reference.
The reference contains a brief description, and examples of use, for each function!

No comments:

Post a Comment

Subscribe to: Post Comments (Atom)