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PHP Keywords
By Shahnail Khan Last updated : December 7, 2023
Like any programming language, PHP has its set of reserved words known as keywords. In this tutorial, we'll explore PHP keywords, including their definition, and syntax.
PHP Keywords
Keywords have specific meanings in the language and cannot be used for naming variables, functions, or classes.
PHP Keywords List
|
Keyword
|
Description
|
Syntax
|
|
abstract
|
Used to declare an abstract class or method
|
abstract class Shape { abstract function draw(); }
|
|
and
|
Logical AND operator
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if ($age >= 18 and $hasID) { ... }
|
|
array
|
Used to declare an array
|
$fruits = array("apple", "banana", "orange");
|
|
as
|
Used to alias a class or function
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use DateTime as MyDate;
|
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break
|
Exits a loop or switch statement
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for ($i = 0; $i < 10; $i++) { if ($i === 5) { break; } }
|
|
callable
|
Represents a callable entity (function or method)
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$callback = function($a, $b) { return $a + $b; };
|
|
case
|
Used in switch statements
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switch ($day) { case "Monday": ...; case "Tuesday": ...; }
|
|
catch
|
Exception handling block
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try { ... } catch (Exception $e) { ... }
|
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class
|
Used to declare a class
|
class User { public $name; public function __construct($name) { $this->name = $name; } }
|
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clone
|
Creates a copy of an object
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$user2 = clone $user1;
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const
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Used to define a constant
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const PI = 3.14159265359;
|
|
continue
|
Skips the current iteration of a loop
|
for ($i = 0; $i < 10; $i++) { if ($i === 5) { continue; } ... }
|
|
declare
|
Declares variables with specific types
|
declare(strict_types=1);
|
|
default
|
Used in switch statements
|
switch ($day) { case "Monday": ...; default: ...; }
|
|
die
|
Prints a message and exits the script
|
die("Error!");
|
|
do
|
Used with while loop to execute code at least once
|
do { ... } while ($condition);
|
|
echo
|
Outputs a string
|
echo "Hello, World!";
|
|
else
|
Used with if statements
|
if ($age >= 18) { ... } else { ... }
|
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elseif
|
Used with if statements as a shortcut for "else if"
|
if ($age >= 21) { ... } elseif ($age >= 18) { ... } else { ... }
|
|
empty
|
Checks if a variable is empty
|
if (empty($name)) { ... }
|
|
enddeclare
|
Used to close a declare block
|
enddeclare();
|
|
endfor
|
Ends a for loop
|
for ($i = 0; $i < 10; $i++) { ... } endfor;
|
|
endforeach
|
Ends a foreach loop
|
foreach ($fruits as $fruit) { ... } endforeach;
|
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endif
|
Ends an if statement
|
if ($age >= 18) { ... } endif;
|
|
endswitch
|
Ends a switch statement
|
switch ($day) { ... } endswitch;
|
|
endwhile
|
Ends a while loop
|
while ($condition) { ... } endwhile;
|
|
eval
|
Evaluates a string as code
|
eval('$result = 1 + 2;');
|
|
exit
|
Prints a message and exits the script
|
exit("Error!");
|
|
extends
|
Used to inherit properties and methods from another class
|
class User extends Person { ... }
|
|
final
|
Prevents a class from being inherited
|
final class Logger { ... }
|
|
finally
|
Always executes after a try/catch block, regardless of whether an exception was thrown
|
try { ... } catch (Exception $e) { ... } finally { ... }
|
|
for
|
Looping structure
|
for ($i = 0; $i < 10; $i++) { ... }
|
|
foreach
|
Looping structure for traversing arrays
|
foreach ($fruits as $fruit) { ... }
|
|
function
|
Used to define a function
|
function sum($a, $b) { return $a + $b; }
|
|
global
|
Used to declare variables accessible within the current scope
|
global $name;
|
|
goto
|
Jump to a specific label within the script
|
goto myLabel;
|
|
if
|
Conditional statement
|
if ($age >= 18) { ... }
|
|
implements
|
Used in a class to implement an interface
|
class MyClass implements MyInterface { ... }
|
|
include
|
Includes and evaluates a specified file
|
include "filename.php";
|
|
include_once
|
Includes and evaluates a file only once
|
include_once "filename.php";
|
|
instanceof
|
Checks if an object is an instance of a class
|
if ($obj instanceof MyClass) { ... }
|
|
insteadof
|
Used in trait to specify a precedence of a certain trait over another
|
use Trait1, Trait2 { Trait1::method insteadof Trait2; }
|
|
interface
|
Declares an interface
|
interface MyInterface { ... }
|
|
isset
|
Checks if a variable is set
|
if (isset($variable)) { ... }
|
|
list
|
Assigns variables as if they were an array
|
list($a, $b) = [1, 2];
|
|
namespace
|
Declares a namespace
|
namespace MyNamespace;
|
|
new
|
Creates a new object
|
$object = new ClassName();
|
|
or
|
Logical OR operator
|
if ($condition1 or $condition2) { ... }
|
|
print
|
Outputs a string
|
print "Hello, World!";
|
|
private
|
Specifies that a method or property can only be accessed within the class
|
private $name;
|
|
protected
|
Specifies that a method or property can only be accessed within the class and its subclasses
|
protected $name;
|
|
public
|
Specifies that a method or property can be accessed from outside the class
|
public $name;
|
|
require
|
Requires and evaluates a specified file
|
require "filename.php";
|
|
require_once
|
Requires and evaluates a file only once
|
require_once "filename.php";
|
|
return
|
Exits a function and returns a value
|
function add($a, $b) { return $a + $b; }
|
|
static
|
Declares a static method or property
|
static $counter = 0;
|
|
switch
|
Selects one of many blocks to be executed
|
switch ($day) { case "Monday": ...; break; }
|
|
throw
|
Throws an exception
|
throw new Exception("Error message");
|
|
trait
|
Introduces a trait into a class
|
class MyClass { use MyTrait; }
|
|
try
|
Implements exception handling
|
try { ... } catch (Exception $e) { ... }
|
|
unset
|
Unsets a variable
|
unset($variable);
|
|
use
|
Imports a namespace or trait
|
use MyNamespace\MyClass;
|
|
var
|
Declares a variable
|
var $name;
|
|
while
|
Creates a while loop
|
while ($condition) { ... }
|
PHP Keywords Examples
Explore these examples to understand about the keywords in PHP scripts.
To understand both of the examples, you should have the knowledge of the following PHP topics:
Example 1
Create a PHP function called divideNumbers that takes two parameters and returns the result of dividing them. Handle division by zero using a try-catch block and throw a custom exception. (Learn: Exception Handling in PHP)
<?php
function divideNumbers($numerator, $denominator)
{
try {
if ($denominator === 0) {
throw new Exception("Cannot divide by zero");
}
return $numerator / $denominator;
} catch (Exception $e) {
echo "Error: " . $e->getMessage();
}
}
$result = divideNumbers(10, 0);
?>
The output of the above example is:
Error: Cannot divide by zero
In this example, we have a function called "divideNumbers" that divides two numbers. The tricky part is, if the second number (denominator) is zero, it can cause an error. So, we use the keywords try, catch, and throw to handle this situation. When the denominator is zero, the program doesn't stop executing; instead, it throws a special message saying "Cannot divide by zero," and the program continues running without any major problems.
Example 2
You are asked to implement a simple arithmetic calculator in PHP. Write a function "calculate" that takes two numbers and an arithmetic operator as parameters and returns the result of the operation.
- The function should handle addition (+), subtraction (-), multiplication (*), and division (/) operations.
- For division, return null if the second number is zero.
- If the operator is not one of the valid arithmetic operators, return null.
Solution
Read the problem carefully. Once you read, think of the easiest approach. Since we have to perform three tasks, we can use the switch statement.
<?php
function calculate($num1, $num2, $operator)
{
switch ($operator) {
case "+":
return $num1 + $num2;
case "-":
return $num1 - $num2;
case "*":
return $num1 * $num2;
case "/":
// Check for division by zero
return $num2 != 0 ? $num1 / $num2 : null;
default:
return null; // Invalid operator
}
}
// Test the function with the provided examples
$result1 = calculate(5, 3, "+");
$result2 = calculate(10, 4, "-");
$result3 = calculate(6, 2, "*");
$result4 = calculate(8, 2, "/");
$result5 = calculate(8, 2, "%");
echo $result1 . "<br>";
echo $result2 . "<br>";
echo $result3 . "<br>";
echo $result4 . "<br>";
var_dump($result5);
?>
The output of the above example is:
8
6
12
4
NULL
This solution uses a switch statement to perform the appropriate arithmetic operation based on the provided operator. The function returns the result of the operation or null for invalid operators or division by zero.