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PHP Syntax

Basic PHP Syntax

A PHP script can be placed anywhere in the document.

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

<?php
// PHP code goes here
?>

The default file extension for PHP files is .php".

A PHP file normally contains HTML tags, and some PHP scripting code.

Below, we have an example of a simple PHP file, with a PHP script that uses a built-in PHP function "echo" to output the text "Hello World!" on a web page:

Example

<!DOCTYPE html>
<html>
<body>
<h1>My first PHP page</h1>
                        
<?php
echo "Hello World!";
?>
                        
</body>
</html>

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>
                        
<h1>My first PHP page</h1>
                        
<?php
echo "Hello World!";
?>
                        
</body>
</html>
PHP Comments

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.

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>
PHP Variables

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;
?>

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!";
?>
PHP echo and print 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().

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.";
?>

The PHP print Statement

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

Example

<?php
print "<h2>PHP is Fun!</h2>";
print "Hello world!<br>";
print "I'm about to learn PHP!";
?>
PHP Data Types

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
  • 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.

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.

Example

$x = true;
$y = false;

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);
?>

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.

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.

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

Example

<?php
$x = "Hello world!";
$x = null;
var_dump($x);
?>
PHP Strings

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.

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

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.

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
?>

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!
?>
PHP Numbers

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

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.

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.

e float data type can commonly store a value up to 1.7976931348623E+308 (platform dependent), and have a maximum precision of 14 digits.

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.

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.

Example

Invalid calculation will return a NaN value:

<?php
$x = acos(8);
var_dump($x);
?>
PHP Math

PHP pi() Function

The pi() function returns the value of PI:

Example

<?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:

Example

<?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:

Example

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

PHP sqrt() Function

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

Example

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

PHP round() Function

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

Example

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

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).

Create a PHP Constant

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

Syntax

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

PHP Constant Arrays

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

Example

Create an Array constant:

<?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.

Example

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

function myTest() {
    echo GREETING;
}
    
myTest();
?>
PHP if else Statements

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.

PHP - The if Statement

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

Example

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.

Example

<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.

Example

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 switch Statement

The PHP switch Statement

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

Example

<?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!";
}
?>
PHP Loops

PHP Loops

Often when you write code, you want the same block of code to run over and over again a certain number of times. So, instead of adding several almost equal code-lines in a script, we can use loops.

Loops are used to execute the same block of code again and again, as long as a certain condition is true.

The PHP while Loop

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

Example

The example below displays the numbers from 1 to 5:

<?php
$x = 1;

while($x <= 5) {
    echo "The number is: $x <br>";
    $x++;
}
?>

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.

Example

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:

<?php
$x = 1;

do {
    echo "The number is: $x <br>";
    $x++;
} while ($x <= 5);
?>

The PHP for Loop

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

Example

The example below displays the numbers from 0 to 10:

<?php
for ($x = 0; $x <= 10; $x++) {
echo "The number is: $x <br>";
}
?>

The PHP foreach Loop

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

Example

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

<?php
$colors = array("red", "green", "blue", "yellow");

foreach ($colors as $value) {
    echo "$value <br>";
}
?>

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:

Example

<?php
for ($x = 0; $x < 10; $x++) {
if ($x == 4) {
break;
}
echo "The number is: $x <br>";
}
?>

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.

Example

This example skips the value of 4:

<?php
for ($x = 0; $x < 10; $x++) {
if ($x == 4) {
continue;
}
echo "The number is: $x <br>";
}
?>
PHP Functions

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.

Please check out our PHP reference for a complete overview of the PHP built-in functions.

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.

Create a User Defined Function in PHP

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

Example

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 ():

<?php
function writeMsg() {
echo "Hello world!";
}

writeMsg(); // call the function
?>
PHP Arrays

What is an Array?

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

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

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

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:

Example

<?php
$cars = array("Volvo", "BMW", "Toyota");
echo count($cars);
?>
PHP Superglobals

PHP Global Variables - Superglobals

Some predefined variables in PHP are "superglobals", which means that they are always accessible, regardless of scope - and you can access them from any function, class or file without having to do anything special.

The PHP superglobal variables are:

  • $GLOBALS
  • $_SERVER
  • $_REQUEST
  • $_POST
  • $_GET
  • $_FILES
  • $_ENV
  • $_COOKIE
  • $_SESSION
PHP RegEx

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.

Using preg_match()

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

Example

Use a regular expression to do a case-insensitive search for "w3schools" in a string:

<?php
$str = "Visit W3Schools";
$pattern = "/w3schools/i";
echo preg_match($pattern, $str); // Outputs 1
?>

Using preg_match_all()

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

Use a regular expression to do a case-insensitive count of the number of occurrences of "ain" in a string:

Example

<?php
$str = "The rain in SPAIN falls mainly on the plains.";
$pattern = "/ain/i";
echo preg_match_all($pattern, $str); // Outputs 4
?>
PHP Form Handling

PHP - A Simple HTML Form

The example below displays a simple HTML form with two input fields and a submit button:

Example

<html>
<body>

<form action="welcome.php" method="post">
Name: <input type="text" name="name"><br>
E-mail: <input type="text" name="email"><br>
<input type="submit">
</form>

</body>
</html>

Example

The same result could also be achieved using the HTTP GET method:

<html>
<body>

<form action="welcome_get.php" method="get">
Name: <input type="text" name="name"><br>
E-mail: <input type="text" name="email"><br>
<input type="submit">
</form>

</body>
</html>
PHP Form Validation

PHP Form Validation

The HTML form we will be working at in these chapters, contains various input fields: required and optional text fields, radio buttons, and a submit button:

Text Fields

The name, email, and website fields are text input elements, and the comment field is a textarea. The HTML code looks like this:

syntax

type="text" name="name">
type="text" name="email">
type="text" name="website">
area name="comment" rows="5" cols="40"></textarea>

Radio Buttons

The gender fields are radio buttons and the HTML code looks like this:

syntax

radio" name="gender" value="female">Female
radio" name="gender" value="male">Male
radio" name="gender" value="other">Other

The Form Element

The HTML code of the form looks like this:

syntax

="post" action="<?php echo htmlspecialchars($_SERVER["PHP_SELF"]);?>">
PHP Form Required

PHP - Required Fields

syntax

<?php
// define variables and set to empty values
$nameErr = $emailErr = $genderErr = $websiteErr = "";
$name = $email = $gender = $comment = $website = "";

if ($_SERVER["REQUEST_METHOD"] == "POST") {
if (empty($_POST["name"])) {
    $nameErr = "Name is required";
} else {
    $name = test_input($_POST["name"]);
}

if (empty($_POST["email"])) {
    $emailErr = "Email is required";
} else {
    $email = test_input($_POST["email"]);
}

if (empty($_POST["website"])) {
    $website = "";
} else {
    $website = test_input($_POST["website"]);
}

if (empty($_POST["comment"])) {
    $comment = "";
} else {
    $comment = test_input($_POST["comment"]);
}

if (empty($_POST["gender"])) {
    $genderErr = "Gender is required";
} else {
    $gender = test_input($_POST["gender"]);
}
}
?>

PHP - Display The Error Messages

Then in the HTML form, we add a little script after each required field, which generates the correct error message if needed (that is if the user tries to submit the form without filling out the required fields):

Example

<form method="post" action="<?php echo htmlspecialchars($_SERVER["PHP_SELF"]);?>">

Name: <input type="text" name="name">
<span class="error">* <?php echo $nameErr;?></span>
<br><br>
E-mail:
<input type="text" name="email">
<span class="error">* <?php echo $emailErr;?></span>
<br><br>
Website:
<input type="text" name="website">
<span class="error"><?php echo $websiteErr;?></span>
<br><br>
Comment: <textarea name="comment" rows="5" cols="40"></textarea>
<br><br>
Gender:
<input type="radio" name="gender" value="female">Female
<input type="radio" name="gender" value="male">Male
<input type="radio" name="gender" value="other">Other
<span class="error">* <?php echo $genderErr;?></span>
<br><br>
<input type="submit" name="submit" value="Submit">

</form>
PHP Form URL/E-mail

PHP - Validate Name

The code below shows a simple way to check if the name field only contains letters, dashes, apostrophes and whitespaces. If the value of the name field is not valid, then store an error message:

syntax

$name = test_input($_POST["name"]);
if (!preg_match("/^[a-zA-Z-' ]*$/",$name)) {
$nameErr = "Only letters and white space allowed";
}

PHP - Validate E-mail

The easiest and safest way to check whether an email address is well-formed is to use PHP's filter_var() function.

In the code below, if the e-mail address is not well-formed, then store an error message:

syntax

put($_POST["email"]);
$email, FILTER_VALIDATE_EMAIL)) {
alid email format";

PHP - Validate URL

The code below shows a way to check if a URL address syntax is valid (this regular expression also allows dashes in the URL). If the URL address syntax is not valid, then store an error message

syntax

input($_POST["website"]);
"/\b(?:(?:https?|ftp):\/\/|www\.)[-a-z0-9+&@#\/%?=~_|!:,.;] * [-a-z0-9+&@#\/%=~_|]/i",$website)) {
nvalid URL";

PHP - Validate Name, E-mail, and URL

Now, the script looks like this:

Example

<?php
// define variables and set to empty values
$nameErr = $emailErr = $genderErr = $websiteErr = "";
$name = $email = $gender = $comment = $website = "";

if ($_SERVER["REQUEST_METHOD"] == "POST") {
if (empty($_POST["name"])) {
    $nameErr = "Name is required";
} else {
$name = test_input($_POST["name"]);
// check if name only contains letters and whitespace
if (!preg_match("/^[a-zA-Z-' ]*$/",$name)) {
    $nameErr = "Only letters and white space allowed";
}
}

if (empty($_POST["email"])) {
    $emailErr = "Email is required";
} else {
    $email = test_input($_POST["email"]);
    
// check if e-mail address is well-formed
if (!filter_var($email, FILTER_VALIDATE_EMAIL)) {
    $emailErr = "Invalid email format";
}
}

if (empty($_POST["website"])) {
    $website = "";
} else {
    $website = test_input($_POST["website"]);

// check if URL address syntax is valid (this regular expression also allows dashes in the URL)
if (!preg_match("/\b(?:(?:https?|ftp):\/\/|www\.)[-a-z0-9+&@#\/%?=~_|!:,.;]*[-a-z0-9+&@#\/%=~_|]/i",$website)) {
    $websiteErr = "Invalid URL";
}
}

if (empty($_POST["comment"])) {
    $comment = "";
} else {
$comment = test_input($_POST["comment"]);
}

if (empty($_POST["gender"])) {
    $genderErr = "Gender is required";
} else {
    $gender = test_input($_POST["gender"]);
}
}
?>
PHP Form Complete

PHP - Keep The Values in The Form

To show the values in the input fields after the user hits the submit button, we add a little PHP script inside the value attribute of the following input fields: name, email, and website. In the comment textarea field, we put the script between the <textarea> and </textarea> tags. The little script outputs the value of the $name, $email, $website, and $comment variables.

Then, we also need to show which radio button that was checked. For this, we must manipulate the checked attribute (not the value attribute for radio buttons):

Example

Name: <input type="text" name="name" value="<?php echo $name;?>">

E-mail: <input type="text" name="email" value="<?php echo $email;?>">

Website: <input type="text" name="website" value="<?php echo $website;?>">

Comment: <textarea name="comment" rows="5" cols="40"><?php echo $comment;?></textarea>

Gender:
<input type="radio" name="gender"
<?php if (isset($gender) && $gender=="female") echo "checked";?>
value="female">Female
<input type="radio" name="gender"
<?php if (isset($gender) && $gender=="male") echo "checked";?>
value="male">Male
<input type="radio" name="gender"
<?php if (isset($gender) && $gender=="other") echo "checked";?>
value="other">Other