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PHP Keywords

Introduction of PHP Keywords

Keywords are the words hold some meaning. In regular use of PHP language, these words cannot be used as a constant, a variable name, a method name, a class name, etc. These keywords when used are automatically understood by PHP. These PHP keywords, when used with variable names, can be confused with the actual keywords. Therefore, these keywords should not be used as variable names.

List of all PHP keywords

Following is a list:

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PHP Keywords

Keyword: abstract

Code:

<?php
//example to demonstrate abstract keyword
abstract class Program {
abstract protected function MethodOne();
public function display() {
echo '<br>'.$this->MethodOne();
}
}
class ProgramOne extends Program {
protected function MethodOne() {
echo '<br>'.'In MethodOne';
}
}
$objOne = new ProgramOne;
$objOne->display();
?>,

Output:

in method one

Keyword: and

Code :

<?php
//example to demonstrate and keyword
$a = 10;
$b = 11;
if($a ==10  and  $b == 11) {
echo 'Result :  True';
}
else
{
echo 'Result : False';
}
?>

Output: 

result two

Keyword: array()

Code:

<?php
//example to demonstrate array keyword
$directions  = array("e" => "east", "w" => "west", "n" => "north", "s" => "south");
print_r($directions);
?>

Output:

array

Keyword: as

Code:

<?php
//example to demonstrate array keyword
$directions  = array("e" => "east", "w" => "west", "n" => "north", "s" => "south");
foreach($directions as $key=>$value) {
echo '<br>'. $key. '=>'.$value;
}
?>

Output:

php keywords.4

Keyword: break

Code :

<?php
//use of break keyword without optional argument
$arr = array("water", "sky", "try", "sand");
foreach($arr as $key=>$value) {
if($value  == 'try') {
break ;          // can use break 1 also
}
echo '<br>'.$value;
}
?>

Output:

water sky

Keyword: case

Code:

<?php
//example to demonstrate case keyword
$i = 1;
while($i<5) {
switch($i) {
case 1:
echo "<br>"."One";
break;
case 2:
echo "<br>"."Two";
break;
case 3:
echo "<br>"."Three";
break;
default:
echo "<br>"."Default";
}
$i++;
}
?>

Output: 

default

Keyword:  catch

Code:

<?php
//example to demonstrate catch keyword
function Operation()
{
try {
$num1 = 10;
$num2 = 0;
if($num1 / $num2) {
throw new Exception('Divide By Zero');
}
} catch (Exception $e) {
die($e->getMessage());
}
}
Operation();
?>

Output:

warning

Keyword: class

Code:

<?php
//example to demonstrate class keyword
class ClassOne{
var $str = 'Hello World';
public function displayMethod() {
echo $this->str;
}
}
$obj = new ClassOne;
$obj->displayMethod();
?>

Output:

hello world

Keyword: const

the const keyword is used to define the name with a value using assignment operator like below

const AGE= 29;

There is no $ sign at the beginning of a constant name like a normal variable has.

Keyword: default

Code:

<?php
// example to demonstrate default keyword
$fruits = 'Cherries';
switch ($fruits) {
case 'Apple':
echo "Apple";
break;
case 'Banana':
echo "Banana";
break;
case 'Papaya':
echo "Papaya";
break;
default:
echo "Fruit is not Apple, Banana or Papaya ";
break;
}
?>

Output :

fruits

Keyword: do

Code:

<?php
// example to demonstrate do keyword
$x = 2;
do {
if($x > 2)
{
echo 'x is greater than 2';
}
else{
echo 'x is less than 2';
}
} while ($x < 2);
?>

Output:

x is less than 2

Keyword: die();

Code :

<?php
//example to demonstrate die keyword
$conn = mysqli_connect('localhost','root','','dbname');
if(!$conn) {
die("Unable to connect ");
}
?>

Output:

unknown database

Keyword: echo

Code:

<?php
// example to demonstrate echo keyword
echo 'Hello! ';
$name = 'John Doe';
echo 'My name is '. $name;
?>

Output:

php keywords.12

Keyword: else

Code:

<?php
// example to demonstrate else keyword
$a = 10;
if ($a > 5) {
echo "a is greater than 10";
} else {
echo "a is not greater than 10";
}
?>

Output:

php keywords.13

Keyword: elseif

Code:

<?php
// example to demonstrate elseif keyword
$a = 10;
if ($a > 10) {
echo "a is greater than 10";
} elseif ($a == 10) {
echo "a is equal to 10";
} else {
echo "a is smaller than 10";
}
?>

Output :

a is equal to 10

Keyword: empty

Code:

<?php
// example to demonstrate empty keyword
$str = 'Hello World!';
if(empty($str)) {
echo 'Variable is empty';
} else {
echo $str;
}
?>

Output:

php keywords.15

Keyword: endfor

Code:

<?php
// example to demonstrate endfor keyword
for($i=0;$i<5;$i++) :
echo "<br/>".$i;
endfor;
?>

Output:

php keywords.16

Keyword: endif

Code :

<?php
// example to demonstrate endif keyword
if ($a > 10):
echo "a is greater than 10";
elseif ($a >10) :
echo "a is equal to 10";
else:
echo "a is not equal to 10";
endif;
?>

Output:

php keywords.17

Keyword: endforeach

 Code:

<?php
// example to demonstrate endforeach keyword
$arr = array(1,2,3,4,5,6,7,8,9,10);
foreach ($arr as $key=>$value):
echo '<br>'.$value;
endforeach;
?>

Output:

php keywords.18

Keyword: endswitch

Code:

<?php
// example to demonstrate endswitch keyword
$fruits = 'Cherries';
switch ($fruits):
case 'Apple':
echo "Apple";
break;
case 'Banana':
echo "Banana";
break;
case 'Papaya':
echo "Papaya";
break;
default:
echo "Fruit is not Apple, Banana or Papaya ";
break;
endswitch;
?>

Output:

php keywords.19

Keyword: endwhile

Code:

<?php
// example to demonstrate endwhile keyword
$i = 0;
while($i<5):
echo "<br>".$i;
$i++;
endwhile;
?>

Output:

php keywords.20

Keyword: eval()

Code:

<?php
//example to demonstrate eval keyword
$string1 = 'World';
$string2 = 'John Doe';
$string = 'Hello $string1 .  My name is $string2';
echo "<br>".$string;
eval("\$string = \"$string\";");
echo "<br>".$string;
?>

Output:

eval

Keyword: exit()

This keyword when encountered in a script, terminates the execution of the script.

Keyword: extends()

Code:

<?php
//example to demonstrate extends keyword
class ParentClass {
var $string = 'PHP';
public function display() {
echo $this->string;
}
}
class ExtendClass extends ParentClass {
public function display() {
echo 'Hello World!';
}
}
$obj1 = new ExtendClass;
$obj1->display();
?>

Output:

extends

Keyword: final

Code:

<?php
//example to demonstrate final keyword
class ParentClass {
var $string = 'PHP';
final public function display() {
echo $this->string;
}
}
class ExtendClass extends ParentClass {
public function display() {
echo 'Hello World!';
}
}
$obj1 = new ExtendClass;
$obj1->display();
?>

Output :

final

Keyword: catch

Code:

<?php
//example to demonstrate catch keyword
try {
$num1 = 10;
$num2 = 0;
if($num1 / $num2) {
throw new Exception('Divide By Zero');
}
} catch (Exception $e) {
echo '<br>'.$e->getMessage();
}
?>

Output:

catch

Keyword: for

Code:

<?php
// example to demonstrate for keyword
for($i=0; $i<10; $i++) {
if($i == 5) {
break;
}
echo '<br>'.$i;
}
?>

Output :

for

Keyword: foreach

Code:

<?php
// example to demonstrate foreach keyword
$array = array(10,20,30,40,50);
foreach($array as $value) {
echo '<br>'.$value/10;
}
?>

Output:

foreach

Keyword: function()

Code:

<?php
function calSum($a , $b) {
$c = $a + $b;
return $c;
}
$result = calSum(10 , 20);
echo '<br> The sum  :  '.$result;
?>

Output:

function

Keyword 34: global

Code:

<?php
//example to demonstrate global keyword
$a = 10;
$b = 20;
function fun() {
global $a;
global $b;
$result = $a + $b;
return $result;
}
$f = fun();
echo 'The result is '.$f;
?>

Output:

global

Keyword: if

Code:

<?php
// example to demonstrate if keyword
$sum = 10;
if($sum == 10) {
echo 'Sum is 10';
} else {
echo 'Sum is not 10';
}
?>

Output:

if

Keyword: implements

Code:

<?php
//example to demonstrate interface keyword
interface One
{
public function first();
}
class MainClass implements One {
public function first() {
echo 'This is the First function';
}
}
$obj = new MainClass;
echo $obj->first();
?>

Output :

implements

Keyword: include

Code:

file.php

<?php
//example to demonstrate include keyword
$a = 'The Earth';
$b = 'Round';
?>

index.php

<?php
include 'file.php';
echo $a . ' is '. $b. ' in Shape';
?>

Keyword  : include_once

Code:

file.php

<?php
//example to demonstrate include_once keyword
$a = 'The Earth';
$b = 'Round';
?>

index.php

<?php
Include_once 'file.php';
echo $a . ' is '. $b. ' in Shape';
?>

Output:

include once

Keyword: instanceOf

Code:

<?php
//example to demonstrate instanceOf keyword
class MainClass
{
public function MainCLassMethod(){
echo 'Hello World!';
}
}
class ExtendedClass extends MainClass
{
public function ExtendedClassMethod(){
echo 'Have a Nice Day!';
}
}
$obj1 = new ExtendedClass;
var_dump($obj1 instanceOf ExtendedClass);
?>

Output:

instanceof

Keyword: Interface

Code:

<?php
//example to demonstrate interface keyword
interface One
{
public function one();
}
interface Two
{
public function two();
}
class MainClass implements One, Two {
public function one() {
echo '<br> This is the one function';
}
public function two() {
echo '<br> This is the two function';
}
}
$obj = new MainClass;
echo $obj->one();
echo $obj->two();
?>

Output:

interface

Keyword: isset

Code:

<?php
//example to demonstrate isset keyword
$stringOne = '';
var_dump(isset($stringOne));
$stringTwo = NULL;
var_dump(isset($stringTwo));
?>

Output :

isset

Keyword: list

Code:

<?php
//example to demonstrate list keyword
$names = array('Ram','Mohan','Raghav');
list($person1, $person2, $person3) = $names;
echo "$person1, $person2 and $person3 are friends";
?>

Output:

list

Keyword: new

Code:

<?php
//example to demonstrate new keyword
class Student
{
public function score($name, $subject, $marks) {
echo "$name scored $marks marks in $subject";
}
}
$obj = new Student;
$obj->score('Sunil','Maths',90);
?>

Output:

new

Keyword: or

Code:

<?php
//example to demonstrate or keyword
$a = 10;
$b = 11;
if($a ==10  or $b == 12) {
echo 'Result :  True';
}
else
{
echo 'Result : False';
}
?>

Output :

or

Keyword: print

Code:

<?php
//example to demonstrate print keyword
$str = "PHP Programming";
print($str);
$stringOne = "Shyam, ";
$stringTwo = "How are you?";
print "<br>"."Hello $stringOne $stringTwo";
?>

Output :

print

Keyword: private

Code:

<?php
//example to demonstrate private keyword
class MainClass
{
private $str = 'Private';
function PrivateMethod()
{
echo 'In '. $this->str. ' Method';
}
}
$obj = new MainClass();
$obj->PrivateMethod(); //Shows Private Method
?>

Output:

private

Keyword: public

Code:

<?php
//example to demonstrate public keyword
class MainClass
{
public $str = 'Public';
function PublicMethod()
{
echo 'In '. $this->str. ' Method';
}
}
$obj = new MainClass();
$obj->PublicMethod(); //Shows Public Method
?>

Output:

public

Keyword: protected

Code:

<?php
//example to demonstrate protected keyword
class MainClass
{
protected $str = 'Protected';
function ProtectedMethod()
{
echo 'In '. $this->str. ' Method';
}
}
$obj = new MainClass();
$obj->ProtectedMethod(); //Shows Protected Method
?>

 Output:

protected

Keyword: return

Code:

<?php
//example to demonstrate return keyword
function sum() {
$a = 10;
$b = 20;
$c = $a +$b;
return $c;
}
$result = sum();
echo 'Sum : ' . $result;
?>

Output:

return

Keyword: switch

Code:

<?php
//example to demonstrate switch keyword
$i= 3;
switch($i) {
case 1:
echo "<br>"."One";
break;
case 2:
echo "<br>"."Two";
break;
case 3:
echo "<br>"."Three";
break;
default:
echo "<br>"."Default";
}
?>

Output:

PHP Keywords - switch output

Keyword: throw

Code:

<?php
//example to demonstrate throw keyword
function division($x, $y) {
try {
if($y == 0) {
throw new Exception('Divide By Zero');
}
}
catch (Exception $e) {
echo '<br>'.$e->getMessage();
}
}
division(10,0);
?>

Output:

PHP Keywords - throw output

Keyword: Try

Code:

<?php
//example to demonstrate try keyword
try{
$arr = array();
$arr_length = count($arr);
if($arr_length == 0) {
throw new Exception('Error : Empty Array!');
}
else {
echo 'Array found';
print_r($arr);
}
}
catch(Exception $e) {
echo '<br>'.$e->getMessage();
}
?>

Output:

PHP Keywords - try output

Keyword: unset

Code:

<?php
//example to demonstrate unset keyword
echo 'Hello World!'.'<br>';
$a = 10;
echo $a;
unset($a);
// echo $a; //this line when uncommented shows error : Undefined variable,  as the variable is unset
?>

Output:

PHP Keywords - unset output

Keyword: var

Code:

<?php
//example to demonstrate var keyword
class MainClass
{
var $str = 'PHP Programming';
public function displayMsg() {
echo $this->str;
}
}
$obj = new MainClass;
$obj->displayMsg();
?>

Output:

PHP Keywords - var Output

Keyword: while

Code: 

<?php
//example to demonstrate while keyword
$i = 0;
while ($i<10) {
echo '<br>'. $i;
$i++;
}
?>

 Output:

PHP Keywords - while

Conclusion

 In this article, you will learn about keywords in PHP with examples. These examples explain the usage of each of the keyword in PHP.

Recommended Articles

This is a guide to the PHP keywords. Here we discuss the Introduction to PHP keywords List of all PHP keywords along with keywords and outputs. You can also go through our other suggested articles to learn more–

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