php13

Easy Learning with "Show PHP"

Our "Show PHP" tool makes it easy to learn PHP, it shows both the PHP source code and the HTML output of the code.

Example

<!DOCTYPE html>
<html>
<body>

<?php
echo "My first PHP script!";
?>


</body>
</html>

 

PHP scripts are executed on the server.


What You Should Already Know

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

  • HTML
  • CSS
  • JavaScript

If you want to study these subjects first, find the tutorials on our Home page.


What is PHP?

  • PHP is an acronym 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 is an amazing and popular language!

It is powerful enough to be at the core of the biggest blogging system on the web (WordPress)!
It is deep enough to run the largest social network (Facebook)!
It is also easy enough to be a beginner's first server side language!


What is a PHP File?

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

What Can PHP Do?

  • PHP can generate dynamic page content
  • PHP can create, open, read, write, delete, 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 be used to control user-access
  • 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.


Why PHP?

  • PHP runs on various platforms (Windows, Linux, Unix, Mac OS X, etc.)
  • PHP is compatible with almost all servers used today (Apache, IIS, etc.)
  • PHP supports a wide range of databases
  • PHP is free. Download it from the official PHP resource: www.php.net
  • PHP is easy to learn and runs efficiently on the server side

Basic PHP Syntax

A PHP script can be placed anywhere in the document.

A PHP script starts with <?php and ends with ?>:

<?php
// 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 file, with a PHP script that uses a built-in PHP function "echo" to output the text "Hello World!" on a web page:

Example

<!DOCTYPE html>
<html>
<body>

<h1>My first PHP page</h1>

<?php
echo "Hello World!";
?>

</body>
</html>
Run example »
 

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


Comments in PHP

A comment in PHP code is a line that is not read/executed as 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 what you are doing
  • 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

<!DOCTYPE html>
<html>
<body>

<?php
// This is a single-line comment

# This is also a single-line comment

/*
This is a multiple-lines comment block
that spans over multiple
lines
*/

// You can also use comments to leave out parts of a code line
$x = 5 /* + 15 */ + 5;
echo $x;
?>

</body>
</html>
Run example »
 

PHP Case Sensitivity

In PHP, all keywords (e.g. if, else, while, echo, etc.), classes, functions, and user-defined functions are NOT case-sensitive.

In the example below, all three echo statements below are legal (and equal):

Example

<!DOCTYPE html>
<html>
<body>

<?php
ECHO "Hello World!<br>";
echo "Hello World!<br>";
EcHo "Hello World!<br>";
?>

</body>
</html>
Run example »
 

However; all variable names are case-sensitive.

In 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):

Example

<!DOCTYPE html>
<html>
<body>

<?php
$color = "red";
echo "My car is " . $color . "<br>";
echo "My house is " . $COLOR . "<br>";
echo "My boat is " . $coLOR . "<br>";
?>

</body>
</html>
Run example»
 

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:

Example

<?php
$txt = "Hello world!";
$x = 5;
$y = 10.5;

echo $txt ;

echo $x ;
echo $y ;
?>
Run example »
 

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:

Example

<?php
$txt = "W3Schools.com";
echo "I love $txt!";
?>
Run example »
 

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

Example

<?php
$txt = "W3Schools.com";
echo "I love " . $txt . "!";
?>
Run example »
 

The following example will output the sum of two variables:

Example

<?php
$x = 5;
$y = 4;
echo $x + $y;
?>
Run example »
 

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

In other languages such as C, C++, and Java, the programmer must declare the name and type of the variable before using it.


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:

  • local
  • global
  • static

Global and Local Scope

A variable declared outside a function has a GLOBAL SCOPE and can only be accessed outside a function:

Example

<?php
$x = 5; // global scope

function myTest() {
    // using x inside this function will generate an error
    echo "<p>Variable x inside function is: $x</p>";
}
myTest();

echo "<p>Variable x outside function is: $x</p>";
?>
Run example »
 

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

Example

<?php
function myTest() {
    $x = 5; // local scope
    echo "<p>Variable x inside function is: $x</p>";
}
myTest();

// using x outside the function will generate an error
echo "<p>Variable x outside function is: $x</p>";
?>
Run example »
 

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):

Example

<?php
$x = 5;
$y = 10;

function myTest() {
    global $x, $y;
    $y = $x + $y;
}

myTest();
echo $y; // outputs 15
?>
Run example »
 

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:

Example

<?php
$x = 5;
$y = 10;

function myTest() {
    $GLOBALS['y'] = $GLOBALS['x'] + $GLOBALS['y'];
}

myTest();
echo $y; // outputs 15
?>
Run example »
 

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:

Example

<?php
function myTest() {
    static $x = 0;
    echo $x;
    $x++;
}

myTest();
myTest();
myTest();
?>
Run example »
 

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.

PHP 5 echo and print Statements


In PHP there are two basic ways to get output: echo and print.

In this tutorial we use echo (and print) in almost every example. So, this chapter contains a little more info about those two output statements.


 


The PHP echo Statement

The echo statement can be used with or without parentheses: echo or echo().

Display Text

The following example shows how to output text with the echo command (notice that the text can contain HTML markup):

Example

<?php
echo "<h2>PHP is Fun!</h2>";
echo "Hello world!<br>";
echo "I'm about to learn PHP!<br>";
echo "This ", "string ", "was ", "made ", "with multiple parameters.";
?>
Run example »
 

Display Variables

The following example shows how to output text and variables with the echo statement:

Example

<?php
$txt1 = "Learn PHP";
$txt2 = "W3Schools.com";
$x = 5;
$y = 4;

echo "<h2>$txt1</h2>";
echo "Study PHP at $txt2<br>";
echo $x + $y;
?>
Run example »
 
 

PHP Data Types

 

Variables can store data of different types, and different data types can do different things.

PHP supports the following data types:

  • String
  • Integer
  • Float (floating point numbers - also called double)
  • Boolean
  • Array
  • Object
  • NULL
  • Resource

PHP String

A string is a sequence of characters, like "Hello world!".

A string can be any text inside quotes. You can use single or double quotes:

Example

<?php 
$x = "Hello world!";
$y = 'Hello world!';

echo $x;
echo "<br>";
echo $y;
?>
Run example »
 

PHP Integer

An integer data type is a non-decimal number between -2,147,483,648 and 2,147,483,647.

Rules for integers:

  • An integer must have at least one digit
  • An integer must not have a decimal point
  • An integer can be either positive or negative
  • Integers can be specified in three formats: decimal (10-based), hexadecimal (16-based - prefixed with 0x) or octal (8-based - prefixed with 0)

In the following example $x is an integer. The PHP var_dump() function returns the data type and value:

Example

<?php 
$x = 5985;
var_dump($x);

?>
Run example »
 
 

PHP Float

A float (floating point number) is a number with a decimal point or a number in exponential form.

In the following example $x is a float. The PHP var_dump() function returns the data type and value:

Example

<?php 
$x = 10.365;
var_dump($x);
?>
Run example »
 

PHP Boolean

A Boolean represents two possible states: TRUE or FALSE.

$x = true;
$y = false;

Booleans are often used in conditional testing. You will learn more about conditional testing in a later chapter of this tutorial.


PHP Array

An array stores multiple values in one single variable.

In the following example $cars is an array. The PHP var_dump() function returns the data type and value:

Example

<?php 
$cars = array("Volvo","BMW","Toyota");
var_dump($cars);
?>
Run example »
 

You will learn a lot more about arrays in later chapters of this tutorial.


PHP Object

An object is a data type which stores data and information on how to process that data.

In PHP, an object must be explicitly declared.

First we must declare a class of object. For this, we use the class keyword. A class is a structure that can contain properties and methods:

Example

<?php
class Car {
    function Car() {
        $this->model = "VW";
    }
}

// create an object
$herbie = new Car();

// show object properties
echo $herbie->model;
?>
Run example »
 

You will learn more about objects in a later chapter of this tutorial.


PHP NULL Value

Null is a special data type which can have only one value: NULL.

A variable of data type NULL is a variable that has no value assigned to it.

Tip: If a variable is created without a value, it is automatically assigned a value of NULL.

Variables can also be emptied by setting the value to NULL:

Example

<?php
$x = "Hello world!";
$x = null;
var_dump($x);
?>
Run example »
 

PHP Resource

The special resource type is not an actual data type. It is the storing of a reference to functions and resources external to PHP.

A common example of using the resource data type is a database call.

We will not talk about the resource type here, since it is an advanced topic.

PHP Strings


A string is a sequence of characters, like "Hello world!".


PHP String Functions

In this chapter we will look at some commonly used functions to manipulate strings.


Get The Length of a String

The PHP strlen() function returns the length of a string.

The example below returns the length of the string "Hello world!":

Example

<?php
echo strlen("Hello world!"); 
?>
Run example »

 


Count The Number of Words in a String

The PHP str_word_count() function counts the number of words in a string:

Example

<?php
echo str_word_count("Hello world!"); 
?>
Run example »


Reverse a String

The PHP strrev() function reverses a string:

Example

<?php
echo strrev("Hello world!"); 
?>
Run example »


Search For a Specific Text Within a String

The PHP strpos() function searches for a specific text within a string.

If a match is found, the function returns the character position of the first match. If no match is found, it will return FALSE.

The example below searches for the text "world" in the string "Hello world!":

Example

<?php
echo strpos("Hello world!", "world");
?>
Run example »

Tip: The first character position in a string is 0 (not 1).


Replace Text Within a String

The PHP str_replace() function replaces some characters with some other characters in a string.

The example below replaces the text "world" with "Dolly":

Example

<?php
echo str_replace("world", "Dolly", "Hello world!"); // outputs Hello Dolly!
?>
Run example »


Complete PHP String Reference

For a complete reference of all string functions, go to our complete PHP String Reference.

The PHP string reference contains description and example of use, for each function!


 
 
 

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