PHP


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
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
·        PHP Installation
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
PHP Syntax
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>
PHP Variables
Variables are "containers" for storing information.
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 of null.
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.
PHP String Variables
A string variable is used to store and manipulate text.
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.

PHP Functions

The real power of PHP comes from its functions.
In PHP, there are more than 700 built-in functions.

PHP Built-in Functions

For a complete reference and examples of the built-in functions, please visit our PHP Reference.

PHP Functions

In this chapter we will show you how to create your own functions.
To keep the script from being executed when the page loads, you can put it into a function.
A function will be executed by a call to the function.
You may call a function from anywhere within a page.

Create a PHP Function

A function will be executed by a call to the function.

Syntax

function functionName()
{
code to be executed;
}
PHP function guidelines:
  • Give the function a name that reflects what the function does
  • The function name can start with a letter or underscore (not a number)

Example

A simple function that writes my name when it is called:
<html>
<body>

<?php
function writeName()
{
echo "Kai Jim Refsnes";
}

echo "My name is ";
writeName();
?>

</body>
</html>
Output:
My name is Kai Jim Refsnes

PHP Functions - Adding parameters

To add more functionality to a function, we can add parameters. A parameter is just like a variable.
Parameters are specified after the function name, inside the parentheses.

Example 1

The following example will write different first names, but equal last name:
<html>
<body>

<?php
function writeName($fname)
{
echo $fname . " Refsnes.<br />";
}

echo "My name is ";
writeName("Kai Jim");
echo "My sister's name is ";
writeName("Hege");
echo "My brother's name is ";
writeName("Stale");
?>

</body>
</html>
Output:
My name is Kai Jim Refsnes.
My sister's name is Hege Refsnes.
My brother's name is Stale Refsnes.

Example 2

The following function has two parameters:
<html>
<body>

<?php
function writeName($fname,$punctuation)
{
echo $fname . " Refsnes" . $punctuation . "<br />";
}

echo "My name is ";
writeName("Kai Jim",".");
echo "My sister's name is ";
writeName("Hege","!");
echo "My brother's name is ";
writeName("Ståle","?");
?>

</body>
</html>
Output:
My name is Kai Jim Refsnes.
My sister's name is Hege Refsnes!
My brother's name is Ståle Refsnes?

PHP Functions - Return values

To let a function return a value, use the return statement.

Example

<html>
<body>

<?php
function add($x,$y)
{
$total=$x+$y;
return $total;
}

echo "1 + 16 = " . add(1,16);
?>

</body>
</html>
Output:
1 + 16 = 17

PHP Forms and User Input

The PHP $_GET and $_POST variables are used to retrieve information from forms, like user input.

PHP Form Handling

The most important thing to notice when dealing with HTML forms and PHP is that any form element in an HTML page will automatically be available to your PHP scripts.

Example

The example below contains an HTML form with two input fields and a submit button:
<html>
<body>

<form action="welcome.php" method="post">
Name: <input type="text" name="fname" />
Age: <input type="text" name="age" />
<input type="submit" />
</form>

</body>
</html>
When a user fills out the form above and clicks on the submit button, the form data is sent to a PHP file, called "welcome.php":
"welcome.php" looks like this:
<html>
<body>

Welcome <?php echo $_POST["fname"]; ?>!<br />
You are <?php echo $_POST["age"]; ?> years old.

</body>
</html>
Output could be something like this:
Welcome John!
You are 28 years old.
The PHP $_GET and $_POST variables will be explained in the next chapters.

Form Validation

User input should be validated on the browser whenever possible (by client scripts). Browser validation is faster and reduces the server load.
You should consider server validation if the user input will be inserted into a database. A good way to validate a form on the server is to post the form to itself, instead of jumping to a different page. The user will then get the error messages on the same page as the form. This makes it easier to discover the error.

PHP $_GET Variable

In PHP, the predefined $_GET variable is used to collect values in a form with method="get".

The $_GET Variable

The predefined $_GET variable is used to collect values in a form with method="get"
Information sent from a form with the GET method is visible to everyone (it will be displayed in the browser's address bar) and has limits on the amount of information to send.

Example

<form action="welcome.php" method="get">
Name: <input type="text" name="fname" />
Age: <input type="text" name="age" />
<input type="submit" />
</form>
When the user clicks the "Submit" button, the URL sent to the server could look something like this:
http://www.w3schools.com/welcome.php?fname=Peter&age=37
The "welcome.php" file can now use the $_GET variable to collect form data (the names of the form fields will automatically be the keys in the $_GET array):
Welcome <?php echo $_GET["fname"]; ?>.<br />
You are <?php echo $_GET["age"]; ?> years old!

When to use method="get"?

When using method="get" in HTML forms, all variable names and values are displayed in the URL.
Note: This method should not be used when sending passwords or other sensitive information!
However, because the variables are displayed in the URL, it is possible to bookmark the page. This can be useful in some cases.
Note: The get method is not suitable for very large variable values. It should not be used with values exceeding 2000 characters.

PHP $_POST Function

In PHP, the predefined  $_POST variable is used to collect values in a form with method="post".

The $_POST Variable

The predefined $_POST variable is used to collect values from a form sent with method="post".
Information sent from a form with the POST method is invisible to others and has no limits on the amount of information to send.
Note: However, there is an 8 Mb max size for the POST method, by default (can be changed by setting the post_max_size in the php.ini file).

Example

<form action="welcome.php" method="post">
Name: <input type="text" name="fname" />
Age: <input type="text" name="age" />
<input type="submit" />
</form>
When the user clicks the "Submit" button, the URL will look like this:
http://www.w3schools.com/welcome.php
The "welcome.php" file can now use the $_POST variable to collect form data (the names of the form fields will automatically be the keys in the $_POST array):
Welcome <?php echo $_POST["fname"]; ?>!<br />
You are <?php echo $_POST["age"]; ?> years old.

When to use method="post"?

Information sent from a form with the POST method is invisible to others and has no limits on the amount of information to send.
However, because the variables are not displayed in the URL, it is not possible to bookmark the page.

The PHP $_REQUEST Variable

The predefined $_REQUEST variable contains the contents of both $_GET, $_POST, and $_COOKIE.
The $_REQUEST variable can be used to collect form data sent with both the GET and POST methods.

Example

Welcome <?php echo $_REQUEST["fname"]; ?>!<br />
You are <?php echo $_REQUEST["age"]; ?> years old.

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