PHP Introduction

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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.

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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

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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“

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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 or PDF files. You can also output any text, such as XHTML and XML.

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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

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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: <=>)

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PHP Installation

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

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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 .php files, 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.

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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

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PHP Syntax

A PHP script is executed on the server, and the plain HTML result is sent back to the browser.

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Basic PHP Syntax

A PHP script can be placed anywhere in the document.

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

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:

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

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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:

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:

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PHP Comments

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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:

PHP Variables

Variables are “containers” for storing information.

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Creating (Declaring) PHP Variables

In PHP, a variable starts with the $ sign, followed by the name of the variable:

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.

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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)

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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:

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

The following example will output the sum of two variables:

Note: You will learn more about the echo statement and how to output data to the screen in the next chapter.

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PHP Variables Scope

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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

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Global and Local Scope

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

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

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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):

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:

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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:

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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Note: The variable is still local to the function.

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PHP echo and print Statements

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.

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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.

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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):

Display Variables

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

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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):

Display Variables

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

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

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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:

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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:

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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:

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PHP Boolean

A Boolean represents two possible states: TRUE or FALSE.

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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:

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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.

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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:

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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!”.

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PHP String Functions

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

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strlen() – Return the Length of a String

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

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str_word_count() – Count Words in a String

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

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strrev() – Reverse a String

The PHP strrev() function reverses a string.

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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.

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

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str_replace() – Replace Text Within a String

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

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PHP Numbers

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.

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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.

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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).

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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()

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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.

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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_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()

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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:

• is_finite()
• is_infinite()

However, the PHP var_dump() function returns the data type and value:

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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:

• is_nan()

However, the PHP var_dump() function returns the data type and value:

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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.

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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.

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PHP Math

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PHP has a set of math functions that allows you to perform mathematical tasks on numbers.

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PHP pi() Function

The pi() function returns the value of PI:

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PHP min() and max() Functions

The min() and max() functions can be used to find the lowest or highest value in a list of arguments:

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PHP abs() Function

The abs() function returns the absolute (positive) value of a number:

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PHP sqrt() Function

The sqrt() function returns the square root of a number:

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PHP round() Function

The round() function rounds a floating-point number to its nearest integer:

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Random Numbers

The rand() function generates a random number:

To get more control over the random number, you can add the optional min and max parameters to specify the lowest integer and the highest integer to be returned.

For example, if you want a random integer between 10 and 100 (inclusive), use rand(10, 100):

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PHP Constants

A constant is an identifier (name) for a simple value. The value cannot be changed during the script.

A valid constant name starts with a letter or underscore (no $ sign before the constant name).

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Note: Unlike variables, constants are automatically global across the entire script.

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Create a PHP Constant

To create a constant, use the define() function.

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Syntax

Parameters:

• name: Specifies the name of the constant
• value: Specifies the value of the constant
• case-insensitive: Specifies whether the constant name should be case-insensitive. Default is false. Note: Defining case-insensitive constants was deprecated in PHP 7.3. PHP 8.0 accepts only false, the value true will produce a warning.

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PHP const Keyword

You can also create a constant by using the const keyword.

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PHP Constant Arrays

In PHP7, you can create an Array constant using the define() function.

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Constants are Global

Constants are automatically global and can be used across the entire script.

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PHP Magic Constants

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PHP Predefined Constants

PHP has nine predefined constants that change value depending on where they are used, and therefor they are called “magic constants”.

These magic constants are written with a double underscore at the start and the end, except for the ClassName::class constant.

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Magic Constants

Here are the magic constants, with descriptions and examples:

Constant	Description
__CLASS__	If used inside a class, the class name is returned.
__DIR__	The directory of the file.
__FILE__	The file name including the full path.
__FUNCTION__	If inside a function, the function name is returned.
__LINE__	The current line number.
__METHOD__	If used inside a function that belongs to a class, both class and function name is returned.
__NAMESPACE__	If used inside a namespace, the name of the namespace is returned.
__TRAIT__	If used inside a trait, the trait name is returned.
ClassName::class	Returns the name of the specified class and the name of the namespace, if any.

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PHP Operators

Operators are used to perform operations on variables and values.

PHP divides the operators in the following groups:

• Arithmetic operators
• Assignment operators
• Comparison operators
• Increment/Decrement operators
• Logical operators
• String operators
• Array operators
• Conditional assignment operators

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PHP Arithmetic Operators

The PHP arithmetic operators are used with numeric values to perform common arithmetical operations, such as addition, subtraction, multiplication etc.

Operator	Name	Example	Result
+	Addition	$x + $y	Sum of $x and $y
–	Subtraction	$x – $y	Difference of $x and $y
*	Multiplication	$x * $y	Product of $x and $y
/	Division	$x / $y	Quotient of $x and $y
%	Modulus	$x % $y	Remainder of $x divided by $y
**	Exponentiation	$x ** $y	Result of raising $x to the $y’th power

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PHP Assignment Operators

The PHP assignment operators are used with numeric values to write a value to a variable.

The basic assignment operator in PHP is “=”. It means that the left operand gets set to the value of the assignment expression on the right.

Assignment	Same as…	Description
x = y	x = y	The left operand gets set to the value of the expression on the right
x += y	x = x + y	Addition
x -= y	x = x – y	Subtraction
x *= y	x = x * y	Multiplication
x /= y	x = x / y	Division
x %= y	x = x % y	Modulus

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PHP Comparison Operators

The PHP comparison operators are used to compare two values (number or string):

Operator	Name	Example	Result
==	Equal	$x == $y	Returns true if $x is equal to $y
===	Identical	$x === $y	Returns true if $x is equal to $y, and they are of the same type
!=	Not equal	$x != $y	Returns true if $x is not equal to $y
<>	Not equal	$x <> $y	Returns true if $x is not equal to $y
!==	Not identical	$x !== $y	Returns true if $x is not equal to $y, or they are not of the same type
>	Greater than	$x > $y	Returns true if $x is greater than $y
<	Less than	$x < $y	Returns true if $x is less than $y
>=	Greater than or equal to	$x >= $y	Returns true if $x is greater than or equal to $y
<=	Less than or equal to	$x <= $y	Returns true if $x is less than or equal to $y
<=>	Spaceship	$x <=> $y	Returns an integer less than, equal to, or greater than zero, depending on if $x is less than, equal to, or greater than $y. Introduced in PHP 7.

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PHP Increment / Decrement Operators

The PHP increment operators are used to increment a variable’s value.

The PHP decrement operators are used to decrement a variable’s value.

Operator	Name	Description
++$x	Pre-increment	Increments $x by one, then returns $x
$x++	Post-increment	Returns $x, then increments $x by one
–$x	Pre-decrement	Decrements $x by one, then returns $x
$x–	Post-decrement	Returns $x, then decrements $x by one

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PHP Logical Operators

The PHP logical operators are used to combine conditional statements.

Operator	Name	Example	Result
and	And	$x and $y	True if both $x and $y are true
or	Or	$x or $y	True if either $x or $y is true
xor	Xor	$x xor $y	True if either $x or $y is true, but not both
&&	And	$x && $y	True if both $x and $y are true
||	Or	$x || $y	True if either $x or $y is true
!	Not	!$x	True if $x is not true

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PHP String Operators

PHP has two operators that are specially designed for strings.

Operator	Name	Example	Result
.	Concatenation	$txt1 . $txt2	Concatenation of $txt1 and $txt2
.=	Concatenation assignment	$txt1 .= $txt2	Appends $txt2 to $txt1

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PHP Array Operators

The PHP array operators are used to compare arrays.

Operator	Name	Example	Result
+	Union	$x + $y	Union of $x and $y
==	Equality	$x == $y	Returns true if $x and $y have the same key/value pairs
===	Identity	$x === $y	Returns true if $x and $y have the same key/value pairs in the same order and of the same types
!=	Inequality	$x != $y	Returns true if $x is not equal to $y
<>	Inequality	$x <> $y	Returns true if $x is not equal to $y
!==	Non-identity	$x !== $y	Returns true if $x is not identical to $y

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PHP Conditional Assignment Operators

The PHP conditional assignment operators are used to set a value depending on conditions:

Operator	Name	Example	Result
?:	Ternary	$x = expr1 ? expr2 : expr3	Returns the value of $x. The value of $x is expr2 if expr1 = TRUE. The value of $x is expr3 if expr1 = FALSE
??	Null coalescing	$x = expr1 ?? expr2	Returns the value of $x. The value of $x is expr1 if expr1 exists, and is not NULL. If expr1 does not exist, or is NULL, the value of $x is expr2. Introduced in PHP 7

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PHP if…else…elseif Statements

Conditional statements are used to perform different actions based on different conditions.

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PHP Conditional Statements

Very often when you write code, you want to perform different actions for different conditions. You can use conditional statements in your code to do this.

In PHP we have the following conditional statements:

• if statement – executes some code if one condition is true
• if...else statement – executes some code if a condition is true and another code if that condition is false
• if...elseif...else statement – executes different codes for more than two conditions
• switch statement – selects one of many blocks of code to be executed

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PHP – The if Statement

The if statement executes some code if one condition is true.

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Syntax

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PHP – The if…else Statement

The if...else statement executes some code if a condition is true and another code if that condition is false.

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Syntax

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PHP – The if…elseif…else Statement

The if...elseif...else statement executes different codes for more than two conditions.

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Syntax

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Short Hand If

To write shorter code, you can write if statements on one line.

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Short Hand If…Else

If…else statements can also be written in one line, but the syntax is a bit different.

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Nested If

You can have if statements inside if statements, this is called nested if statements.

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PHP switch Statement

The switch statement is used to perform different actions based on different conditions.

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The PHP switch Statement

Use the switch statement to select one of many blocks of code to be executed.

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Syntax

This is how it works: First we have a single expression n (most often a variable), that is evaluated once. The value of the expression is then compared with the values for each case in the structure. If there is a match, the block of code associated with that case is executed. Use break to prevent the code from running into the next case automatically. The default statement is used if no match is found.

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PHP Loops

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The PHP while Loop

The while loop executes a block of code as long as the specified condition is true.

Syntax

Example Explained

• $x = 1; – Initialize the loop counter ($x), and set the start value to 1
• $x <= 5 – Continue the loop as long as $x is less than or equal to 5
• $x++; – Increase the loop counter value by 1 for each iteration

This example counts to 100 by tens:

Example Explained

• $x = 0; – Initialize the loop counter ($x), and set the start value to 0
• $x <= 100 – Continue the loop as long as $x is less than or equal to 100
• $x+=10; – Increase the loop counter value by 10 for each iteration

The do...while loop – Loops through a block of code once, and then repeats the loop as long as the specified condition is true.

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The PHP do…while Loop

The do...while loop will always execute the block of code once, it will then check the condition, and repeat the loop while the specified condition is true.

Syntax

Examples

The example below first sets a variable $x to 1 ($x = 1). Then, the do while loop will write some output, and then increment the variable $x with 1. Then the condition is checked (is $x less than, or equal to 5?), and the loop will continue to run as long as $x is less than, or equal to 5:

This example sets the $x variable to 6, then it runs the loop, and then the condition is checked:

The PHP for Loop

The for loop is used when you know in advance how many times the script should run.

Syntax

Parameters:

• init counter: Initialize the loop counter value
• test counter: Evaluated for each loop iteration. If it evaluates to TRUE, the loop continues. If it evaluates to FALSE, the loop ends.
• increment counter: Increases the loop counter value

Example Explained

• $x = 0; – Initialize the loop counter ($x), and set the start value to 0
• $x <= 10; – Continue the loop as long as $x is less than or equal to 10
• $x++ – Increase the loop counter value by 1 for each iteration

This example counts to 100 by tens:

Example Explained

• $x = 0; – Initialize the loop counter ($x), and set the start value to 0
• $x <= 100; – Continue the loop as long as $x is less than or equal to 100
• $x+=10 – Increase the loop counter value by 10 for each iteration

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The PHP foreach Loop

The foreach loop works only on arrays, and is used to loop through each key/value pair in an array.

Syntax

For every loop iteration, the value of the current array element is assigned to $value and the array pointer is moved by one, until it reaches the last array element.

Examples

The following example will output the values of the given array ($colors):

The following example will output both the keys and the values of the given array ($age):

PHP Break

You have already seen the break statement used in an earlier chapter of this tutorial. It was used to “jump out” of a switch statement.

The break statement can also be used to jump out of a loop.

This example jumps out of the loop when x is equal to 4:

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PHP Continue

The continue statement breaks one iteration (in the loop), if a specified condition occurs, and continues with the next iteration in the loop.

This example skips the value of 4:

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Break and Continue in While Loop

You can also use break and continue in while loops:

The real power of PHP comes from its functions.

PHP has more than 1000 built-in functions, and in addition you can create your own custom functions.

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PHP Built-in Functions

PHP has over 1000 built-in functions that can be called directly, from within a script, to perform a specific task.

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PHP User Defined Functions

Besides the built-in PHP functions, it is possible to create your own functions.

• A function is a block of statements that can be used repeatedly in a program.
• A function will not execute automatically when a page loads.
• A function will be executed by a call to the function.

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Create a User Defined Function in PHP

A user-defined function declaration starts with the word function:

Syntax

Tip: Give the function a name that reflects what the function does!

In the example below, we create a function named “writeMsg()”. The opening curly brace ( { ) indicates the beginning of the function code, and the closing curly brace ( } ) indicates the end of the function. The function outputs “Hello world!”. To call the function, just write its name followed by brackets ():

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PHP Function Arguments

Information can be passed to functions through arguments. An argument is just like a variable.

Arguments are specified after the function name, inside the parentheses. You can add as many arguments as you want, just separate them with a comma.

The following example has a function with one argument ($fname). When the familyName() function is called, we also pass along a name (e.g. Jani), and the name is used inside the function, which outputs several different first names, but an equal last name:

The following example has a function with two arguments ($fname and $year):

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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 us an option to specify the expected data type when declaring a function, and by adding the strict declaration, it will throw a “Fatal Error” if the data type mismatches.

In the following example we try to send both a number and a string to the function without using strict:

To specify strict we need to set declare(strict_types=1);. This must be on the very first line of the PHP file.

In the following example we try to send both a number and a string to the function, but here we have added the strict declaration:

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PHP Default Argument Value

The following example shows how to use a default parameter. If we call the function setHeight() without arguments it takes the default value as argument:

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PHP Functions – Returning values

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

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PHP Return Type Declarations

PHP 7 also supports Type Declarations for the return statement. Like with the type declaration for function arguments, by enabling the strict requirement, it will throw a “Fatal Error” on a type mismatch.

To declare a type for the function return, add a colon ( : ) and the type right before the opening curly ( { )bracket when declaring the function.

In the following example we specify the return type for the function:

You can specify a different return type, than the argument types, but make sure the return is the correct type:

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Passing Arguments by Reference

In PHP, arguments are usually passed by value, which means that a copy of the value is used in the function and the variable that was passed into the function cannot be changed.

When a function argument is passed by reference, changes to the argument also change the variable that was passed in. To turn a function argument into a reference, the & operator is used:

An array stores multiple values in one single variable:

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What is an Array?

An array is a special variable, which can hold more than one value at a time.

If you have a list of items (a list of car names, for example), storing the cars in single variables could look like this:

However, what if you want to loop through the cars and find a specific one? And what if you had not 3 cars, but 300?

The solution is to create an array!

An array can hold many values under a single name, and you can access the values by referring to an index number.

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Create an Array in PHP

In PHP, the array() function is used to create an array:

In PHP, there are three types of arrays:

• Indexed arrays – Arrays with a numeric index
• Associative arrays – Arrays with named keys
• Multidimensional arrays – Arrays containing one or more arrays

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Get The Length of an Array – The count() Function

The count() function is used to return the length (the number of elements) of an array:

PHP Indexed Arrays

There are two ways to create indexed arrays:

The index can be assigned automatically (index always starts at 0), like this:

or the index can be assigned manually:

The following example creates an indexed array named $cars, assigns three elements to it, and then prints a text containing the array values:

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Loop Through an Indexed Array

To loop through and print all the values of an indexed array, you could use a for loop, like this:

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PHP $_SERVER

$_SERVER is a PHP super global variable which holds information about headers, paths, and script locations.

The example below shows how to use some of the elements in $_SERVER:

The following table lists the most important elements that can go inside $_SERVER:

Element/Code	Description
$_SERVER[‘PHP_SELF’]	Returns the filename of the currently executing script
$_SERVER[‘GATEWAY_INTERFACE’]	Returns the version of the Common Gateway Interface (CGI) the server is using
$_SERVER[‘SERVER_ADDR’]	Returns the IP address of the host server
$_SERVER[‘SERVER_NAME’]	Returns the name of the host server (such as www.w3schools.com)
$_SERVER[‘SERVER_SOFTWARE’]	Returns the server identification string (such as Apache/2.2.24)
$_SERVER[‘SERVER_PROTOCOL’]	Returns the name and revision of the information protocol (such as HTTP/1.1)
$_SERVER[‘REQUEST_METHOD’]	Returns the request method used to access the page (such as POST)
$_SERVER[‘REQUEST_TIME’]	Returns the timestamp of the start of the request (such as 1377687496)
$_SERVER[‘QUERY_STRING’]	Returns the query string if the page is accessed via a query string
$_SERVER[‘HTTP_ACCEPT’]	Returns the Accept header from the current request
$_SERVER[‘HTTP_ACCEPT_CHARSET’]	Returns the Accept_Charset header from the current request (such as utf-8,ISO-8859-1)
$_SERVER[‘HTTP_HOST’]	Returns the Host header from the current request
$_SERVER[‘HTTP_REFERER’]	Returns the complete URL of the current page (not reliable because not all user-agents support it)
$_SERVER[‘HTTPS’]	Is the script queried through a secure HTTP protocol
$_SERVER[‘REMOTE_ADDR’]	Returns the IP address from where the user is viewing the current page
$_SERVER[‘REMOTE_HOST’]	Returns the Host name from where the user is viewing the current page
$_SERVER[‘REMOTE_PORT’]	Returns the port being used on the user’s machine to communicate with the web server
$_SERVER[‘SCRIPT_FILENAME’]	Returns the absolute pathname of the currently executing script
$_SERVER[‘SERVER_ADMIN’]	Returns the value given to the SERVER_ADMIN directive in the web server configuration file (if your script runs on a virtual host, it will be the value defined for that virtual host) (such as someone@w3schools.com)
$_SERVER[‘SERVER_PORT’]	Returns the port on the server machine being used by the web server for communication (such as 80)
$_SERVER[‘SERVER_SIGNATURE’]	Returns the server version and virtual host name which are added to server-generated pages
$_SERVER[‘PATH_TRANSLATED’]	Returns the file system based path to the current script
$_SERVER[‘SCRIPT_NAME’]	Returns the path of the current script
$_SERVER[‘SCRIPT_URI’]	Returns the URI of the current page

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PHP $_GET

PHP $_GET is a PHP super global variable which is used to collect form data after submitting an HTML form with method=”get”.

$_GET can also collect data sent in the URL.

Assume we have an HTML page that contains a hyperlink with parameters:

When a user clicks on the link “Test $GET”, the parameters “subject” and “web” are sent to “test_get.php”, and you can then access their values in “test_get.php” with $_GET.

The example below shows the code in “test_get.php”:

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PHP Regular Expressions

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What is a Regular Expression?

A regular expression is a sequence of characters that forms a search pattern. When you search for data in a text, you can use this search pattern to describe what you are searching for.

A regular expression can be a single character, or a more complicated pattern.

Regular expressions can be used to perform all types of text search and text replace operations.

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Syntax

In PHP, regular expressions are strings composed of delimiters, a pattern and optional modifiers.

In the example above, / is the delimiter, w3schools is the pattern that is being searched for, and i is a modifier that makes the search case-insensitive.

The delimiter can be any character that is not a letter, number, backslash or space. The most common delimiter is the forward slash (/), but when your pattern contains forward slashes it is convenient to choose other delimiters such as # or ~.

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Regular Expression Functions

PHP provides a variety of functions that allow you to use regular expressions. The preg_match(), preg_match_all() and preg_replace() functions are some of the most commonly used ones:

Function	Description
preg_match()	Returns 1 if the pattern was found in the string and 0 if not
preg_match_all()	Returns the number of times the pattern was found in the string, which may also be 0
preg_replace()	Returns a new string where matched patterns have been replaced with another string

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Using preg_match()

The preg_match() function will tell you whether a string contains matches of a pattern.

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Using preg_match_all()

The preg_match_all() function will tell you how many matches were found for a pattern in a string.

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Using preg_replace()

The preg_replace() function will replace all of the matches of the pattern in a string with another string.

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Regular Expression Modifiers

Modifiers can change how a search is performed.

Modifier	Description
i	Performs a case-insensitive search
m	Performs a multiline search (patterns that search for the beginning or end of a string will match the beginning or end of each line)
u	Enables correct matching of UTF-8 encoded patterns

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Regular Expression Patterns

Brackets are used to find a range of characters:

Expression	Description
[abc]	Find one character from the options between the brackets
[^abc]	Find any character NOT between the brackets
[0-9]	Find one character from the range 0 to 9

Metacharacters

Metacharacters are characters with a special meaning:

Metacharacter	Description
|	Find a match for any one of the patterns separated by | as in: cat|dog|fish
.	Find just one instance of any character
^	Finds a match as the beginning of a string as in: ^Hello
$	Finds a match at the end of the string as in: World$
\d	Find a digit
\s	Find a whitespace character
\b	Find a match at the beginning of a word like this: \bWORD, or at the end of a word like this: WORD\b
\uxxxx	Find the Unicode character specified by the hexadecimal number xxxx

Quantifiers

Quantifiers define quantities:

Quantifier	Description
n+	Matches any string that contains at least one n
n*	Matches any string that contains zero or more occurrences of n
n?	Matches any string that contains zero or one occurrences of n
n{x}	Matches any string that contains a sequence of X n‘s
n{x,y}	Matches any string that contains a sequence of X to Y n‘s
n{x,}	Matches any string that contains a sequence of at least X n‘s

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Grouping

You can use parentheses ( ) to apply quantifiers to entire patterns. They also can be used to select parts of the pattern to be used as a match.