PHP code is executed on the server.
What You Should Already Know
Before you continue you should have a basic understanding of the following:
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 large social networks!
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 is 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
What's new in PHP 7
- PHP 7 is much faster than the previous popular stable release (PHP 5.6)
- PHP 7 has improved Error Handling
- PHP 7 supports stricter Type Declarations for function arguments
- PHP 7 supports new operators (like the spaceship operator:
<=>) What Do I Need?
To start using PHP, you can:
- Find a web host with PHP and MySQL support
- Install a web server on your own PC, and then install PHP and MySQL
Use a Web Host With PHP Support
If your server has activated support for PHP you do not need to do anything.
Just create some
.phpfiles, place them in your web directory, and the server will automatically parse them for you.You do not need to compile anything or install any extra tools.
Because PHP is free, most web hosts offer PHP support.
Set Up PHP on Your Own PC
However, if your server does not support PHP, you must:
- install a web server
- install PHP
- install a database, such as MySQL
The official PHP website (PHP.net) has installation instructions for PHP: http://php.net/manual/en/install.php
PHP Online Compiler / Editor
With w3schools' online PHP compiler, you can edit PHP code, and view the result in your browser.
<?php
$txt = "PHP";
echo "I love $txt!";
?>I love PHP!Click on the "Try it Yourself" button to see how it works.
A PHP script is executed on the server, and the plain HTML result is sent back to the browser.
Basic PHP Syntax
A PHP script can be placed anywhere in the document.
A PHP script starts with
<?phpand 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>Note: PHP statements end with a semicolon (
;).
PHP Case Sensitivity
In PHP, 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 equal and legal:
Example
<!DOCTYPE html>
<html>
<body>
<?php
ECHO "Hello World!<br>";
echo "Hello World!<br>";
EcHo "Hello World!<br>";
?>
</body>
</html>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:
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>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:
<!DOCTYPE html>
<html>
<body>
<?php
// This is a single-line comment
# This is also a single-line comment
?>
</body>
</html>Example
Syntax for multiple-line comments:
<!DOCTYPE html>
<html>
<body>
<?php
/*
This is a multiple-lines comment block
that spans over multiple
lines
*/
?>
</body>
</html>Example
Using comments to leave out parts of the code:
<!DOCTYPE html>
<html>
<body>
<?php
// You can also use comments to leave out parts of a code line
$x = 5 /* + 15 */ + 5;
echo $x;
?>
</body>
</html>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;
?>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 (
$ageand$AGEare 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!";
?>The following example will produce the same output as the example above:
Example
<?php
$txt = "W3Schools.com";
echo "I love " . $txt . "!";
?>The following example will output the sum of two variables:
Example
<?php
$x = 5;
$y = 4;
echo $x + $y;
?>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.
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
Variable with global scope:
<?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>";
?>A variable declared within a function has a LOCAL SCOPE and can only be accessed within that function:
Example
Variable with local scope:
<?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>";
?>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
?>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
?>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();
?>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.
With PHP, there are two basic ways to get output: echo and print.
In this tutorial we use echo or print in almost every example. So, this chapter contains a little more info about those two output statements.
PHP echo and print Statements
echo and print are more or less the same. They are both used to output data to the screen.
The differences are small: echo has no return value while print has a return value of 1 so it can be used in expressions. echo can take multiple parameters (although such usage is rare) while print can take one argument. echo is marginally faster than print.
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.";
?>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;
?>The PHP print Statement
The print statement can be used with or without parentheses: print or print().
Display Text
The following example shows how to output text with the print command (notice that the text can contain HTML markup):
Example
<?php
print "<h2>PHP is Fun!</h2>";
print "Hello world!<br>";
print "I'm about to learn PHP!";
?>Display Variables
The following example shows how to output text and variables with the print statement:
Example
<?php
$txt1 = "Learn PHP";
$txt2 = "W3Schools.com";
$x = 5;
$y = 4;
print "<h2>" . $txt1 . "</h2>";
print "Study PHP at " . $txt2 . "<br>";
print $x + $y;
?>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;
?>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: decimal (base 10), hexadecimal (base 16), octal (base 8), or binary (base 2) notation
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);
?>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);
?>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);
?>You will learn a lot more about arrays in later chapters of this tutorial.
PHP Object
Classes and objects are the two main aspects of object-oriented programming.
A class is a template for objects, and an object is an instance of a class.
When the individual objects are created, they inherit all the properties and behaviors from the class, but each object will have different values for the properties.
Let's assume we have a class named Car. A Car can have properties like model, color, etc. We can define variables like $model, $color, and so on, to hold the values of these properties.
When the individual objects (Volvo, BMW, Toyota, etc.) are created, they inherit all the properties and behaviors from the class, but each object will have different values for the properties.
If you create a __construct() function, PHP will automatically call this function when you create an object from a class.
Example
<?php
class Car {
public $color;
public $model;
public function __construct($color, $model) {
$this->color = $color;
$this->model = $model;
}
public function message() {
return "My car is a " . $this->color . " " . $this->model . "!";
}
}
$myCar = new Car("black", "Volvo");
echo $myCar -> message();
echo "<br>";
$myCar = new Car("red", "Toyota");
echo $myCar -> message();
?>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);
?>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.
strlen() - Return the Length of a String
The PHP strlen() function returns the length of a string.
Example
Return the length of the string "Hello world!":
<?php
echo strlen("Hello world!"); // outputs 12
?>str_word_count() - Count Words in a String
The PHP str_word_count() function counts the number of words in a string.
Example
Count the number of word in the string "Hello world!":
<?php
echo str_word_count("Hello world!"); // outputs 2
?>strrev() - Reverse a String
The PHP strrev() function reverses a string.
Example
Reverse the string "Hello world!":
<?php
echo strrev("Hello world!"); // outputs !dlrow olleH
?>strpos() - Search For a 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.
Example
Search for the text "world" in the string "Hello world!":
<?php
echo strpos("Hello world!", "world"); // outputs 6
?>Tip: The first character position in a string is 0 (not 1).
str_replace() - Replace Text Within a String
The PHP str_replace() function replaces some characters with some other characters in a string.
Example
Replace the text "world" with "Dolly":
<?php
echo str_replace("world", "Dolly", "Hello world!"); // outputs Hello Dolly!
?>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!
One thing to notice about PHP is that it provides automatic data type conversion.
So, if you assign an integer value to a variable, the type of that variable will automatically be an integer. Then, if you assign a string to the same variable, the type will change to a string.
This automatic conversion can sometimes break your code.
PHP Integers
2, 256, -256, 10358, -179567 are all integers.
An integer is a number without any decimal part.
An integer data type is a non-decimal number between -2147483648 and 2147483647 in 32 bit systems, and between -9223372036854775808 and 9223372036854775807 in 64 bit systems. A value greater (or lower) than this, will be stored as float, because it exceeds the limit of an integer.
Note: Another important thing to know is that even if 4 * 2.5 is 10, the result is stored as float, because one of the operands is a float (2.5).
Here are some 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)
PHP has the following predefined constants for integers:
- PHP_INT_MAX - The largest integer supported
- PHP_INT_MIN - The smallest integer supported
- PHP_INT_SIZE - The size of an integer in bytes
PHP has the following functions to check if the type of a variable is integer:
- is_int()
- is_integer() - alias of is_int()
- is_long() - alias of is_int()
Example
Check if the type of a variable is integer:
<?php
$x = 5985;
var_dump(is_int($x));
$x = 59.85;
var_dump(is_int($x));
?>PHP Floats
A float is a number with a decimal point or a number in exponential form.
2.0, 256.4, 10.358, 7.64E+5, 5.56E-5 are all floats.
The float data type can commonly store a value up to 1.7976931348623E+308 (platform dependent), and have a maximum precision of 14 digits.
PHP has the following predefined constants for floats (from PHP 7.2):
- PHP_FLOAT_MAX - The largest representable floating point number
- PHP_FLOAT_MIN - The smallest representable positive floating point number
- - PHP_FLOAT_MAX - The smallest representable negative floating point number
- PHP_FLOAT_DIG - The number of decimal digits that can be rounded into a float and back without precision loss
- PHP_FLOAT_EPSILON - The smallest representable positive number x, so that x + 1.0 != 1.0
PHP has the following functions to check if the type of a variable is float:
- is_float()
- is_double() - alias of is_float()
Example
Check if the type of a variable is float:
<?php
$x = 10.365;
var_dump(is_float($x));
?>PHP Infinity
A numeric value that is larger than PHP_FLOAT_MAX is considered infinite.
PHP has the following functions to check if a numeric value is finite or infinite:
However, the PHP var_dump() function returns the data type and value:
Example
Check if a numeric value is finite or infinite:
<?php
$x = 1.9e411;
var_dump($x);
?>PHP NaN
NaN stands for Not a Number.
NaN is used for impossible mathematical operations.
PHP has the following functions to check if a value is not a number:
However, the PHP var_dump() function returns the data type and value:
Example
Invalid calculation will return a NaN value:
<?php
$x = acos(8);
var_dump($x);
?>PHP Numerical Strings
The PHP is_numeric() function can be used to find whether a variable is numeric. The function returns true if the variable is a number or a numeric string, false otherwise.
Example
Check if the variable is numeric:
<?php
$x = 5985;
var_dump(is_numeric($x));
$x = "5985";
var_dump(is_numeric($x));
$x = "59.85" + 100;
var_dump(is_numeric($x));
$x = "Hello";
var_dump(is_numeric($x));
?>Note: From PHP 7.0: The is_numeric() function will return FALSE for numeric strings in hexadecimal form (e.g. 0xf4c3b00c), as they are no longer considered as numeric strings.
PHP Casting Strings and Floats to Integers
Sometimes you need to cast a numerical value into another data type.
The (int), (integer), or intval() function are often used to convert a value to an integer.
Example
Cast float and string to integer:
<?php
// Cast float to int
$x = 23465.768;
$int_cast = (int)$x;
echo $int_cast;
echo "<br>";
// Cast string to int
$x = "23465.768";
$int_cast = (int)$x;
echo $int_cast;
?>
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