Learn PHP

PHP is a server scripting language, and a powerful tool for making dynamic and interactive Web pages.

PHP is a widely-used, free, and efficient alternative to competitors such as Microsoft's ASP.

PHP Introduction

PHP code is executed on the server.

What You Should Already Know?

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

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 or PDF files. 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: <=>)

PHP Installation

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 .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.

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 Syntax

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 <?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:

<!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:

<!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:

<!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>

PHP Comments

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:

<!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>

PHP 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:

<?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 ($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:

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

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

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

The following example will output the sum of two variables:

<?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.

You will learn more about strict and non-strict requirements, and data type declarations in the PHP Functions chapter.

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:

<?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:

<?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):

<?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:

<?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:

<?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.

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.

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):

<?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:

<?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):

<?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:

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

  print "<h2>" . $txt1 . "</h2>";
  print "Study PHP at " . $txt2 . "<br>";
  print $x + $y;
?>

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:

<?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:

<?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:

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

PHP Boolean

A Boolean represents two possible states: TRUE or FALSE.

<?php
$x = true;
$y = false;
?>

Booleans are often used in conditional testing.

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:

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

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.

<?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:

<?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.

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.

strlen() - Return the Length of a String

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

<?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.

<?php
echo str_word_count("Hello world!"); // outputs 2
?>

strrev() - Reverse a String The PHP strrev() function reverses a string.

<?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.

<?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.

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

PHP Numbers

In this chapter we will look in depth into Integers, Floats, and Number Strings.

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.

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()

<?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_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()

<?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:

is_finite()
is_infinite()

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

<?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:

is_nan()

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

<?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.

<?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;
?>

PHP Math

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

PHP pi() Function

The pi() function returns the value of PI:

<?php
echo(pi()); // returns 3.1415926535898
?>

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:

<?php
echo(min(0, 150, 30, 20, -8, -200));  // returns -200
echo(max(0, 150, 30, 20, -8, -200));  // returns 150
?>

PHP abs() Function

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

<?php
echo(abs(-6.7));  // returns 6.7
?>

PHP sqrt() Function

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

<?php
echo(sqrt(64));  // returns 8
?>

PHP round() Function

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

<?php
echo(round(0.60));  // returns 1
echo(round(0.49));  // returns 0
?>

Random Numbers

The rand() function generates a random number:

<?php
echo(rand());
?>

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):

<?php
echo(rand(10, 100));
?>

PHP Constants

Constants are like variables except that once they are defined they cannot be changed or undefined.

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).

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

Create a PHP Constant

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

Syntax

define(name, value, case-insensitive)

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

<?php
define("GREETING", "Welcome to W3Schools.com!");
echo GREETING;
?>

<?php
define("GREETING", "Welcome to W3Schools.com!", true);
echo greeting;
?>

PHP Constant Arrays

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

<?php
define("cars", [
  "Alfa Romeo",
  "BMW",
  "Toyota"
]);
echo cars[0];
?>

Constants are Global

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

<?php
define("GREETING", "Welcome to W3Schools.com!");

function myTest() {
  echo GREETING;
}

myTest();
?>

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

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

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

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.

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

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

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

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

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

PHP if...else...elseif Statements

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

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

PHP - The if Statement

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

Syntax

if (condition) {
  code to be executed if condition is true;
}

# Output "Have a good day!" if the current time (HOUR) is less than 20:
<?php
$t = date("H");

if ($t < "20") {
  echo "Have a good day!";
}
?>

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.

Syntax

if (condition) {
  code to be executed if condition is true;
} else {
  code to be executed if condition is false;
}

# Output "Have a good day!" if the current time is less than 20, and "Have a good night!" otherwise:
<?php
$t = date("H");

if ($t < "20") {
  echo "Have a good day!";
} else {
  echo "Have a good night!";
}
?>

PHP - The if...elseif...else Statement

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

Syntax

if (condition) {
  code to be executed if this condition is true;
} elseif (condition) {
  code to be executed if first condition is false and this condition is true;
} else {
  code to be executed if all conditions are false;
}

# Output "Have a good morning!" if the current time is less than 10, and "Have a good day!" if the current time is less than 20. Otherwise it will output "Have a good night!":
<?php
$t = date("H");

if ($t < "10") {
  echo "Have a good morning!";
} elseif ($t < "20") {
  echo "Have a good day!";
} else {
  echo "Have a good night!";
}
?>

PHP - The switch Statement

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

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

Syntax

switch (n) {
  case label1:
    code to be executed if n=label1;
    break;
  case label2:
    code to be executed if n=label2;
    break;
  case label3:
    code to be executed if n=label3;
    break;
    ...
  default:
    code to be executed if n is different from all labels;
}

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.

<?php
$favcolor = "red";

switch ($favcolor) {
  case "red":
    echo "Your favorite color is red!";
    break;
  case "blue":
    echo "Your favorite color is blue!";
    break;
  case "green":
    echo "Your favorite color is green!";
    break;
  default:
    echo "Your favorite color is neither red, blue, nor green!";
}
?>

📜 References

🤝 Contributors

Mengsreang-Chhoeung @mengsreang_dev

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Learn PHP

PHP Introduction

What You Should Already Know?

What is PHP?

PHP is an amazing and popular language!

What is a PHP File?

What Can PHP Do?

Why PHP?

What's new in PHP 7

PHP Installation

Use a Web Host With PHP Support

Set Up PHP on Your Own PC

PHP Syntax

Basic PHP Syntax

PHP Case Sensitivity

PHP Comments

PHP Variables

Creating (Declaring) PHP Variables

PHP Variables

Output Variables

PHP is a Loosely Typed Language

PHP Variables Scope

Global and Local Scope

PHP The global Keyword

PHP The static Keyword

PHP echo and print Statements

PHP echo and print Statements

The PHP echo Statement

The PHP print Statement

PHP Data Types

PHP String

PHP Integer

PHP Float

PHP Boolean

PHP Array

PHP Object

PHP NULL Value

PHP Resource

PHP Strings

PHP String Functions

PHP Numbers

PHP Numbers

PHP Integers

PHP Floats

PHP Infinity

PHP NaN

PHP Numerical Strings

PHP Casting Strings and Floats to Integers

PHP Math

PHP Constants

PHP Constants

Create a PHP Constant

PHP Constant Arrays

Constants are Global

PHP Operators

PHP Arithmetic Operators

PHP Assignment Operators

PHP Comparison Operators

PHP Increment / Decrement Operators

PHP Logical Operators

PHP String Operators

PHP Array Operators

PHP Conditional Assignment Operators

PHP if...else...elseif Statements

PHP Conditional Statements

PHP - The if Statement

PHP - The if...else Statement

PHP - The if...elseif...else Statement

PHP - The switch Statement