Php

Basics

Hello World

The echo statement is used to output strings or variables:

<?php echo "Hello World!"; print "Hello Again!"; // 'print' also works?>

Note: echo can take multiple parameters (though rarely used), while print always returns 1 and takes a single argument.

Comments

Single-line comments

// This is a comment# This is also a comment

Multi-line comments

/*    This is a    multi-line comment*/

Debugging Functions

var_dump($var) → Displays structured info (type + value).
print_r($var) → Prints human-readable info (good for arrays).
var_export($var) → Returns parsable string representation.

<?php$names = ["Harry", "Rohan"];var_dump($names);print_r($names);?>

Variables

Variables start with $.
Case-sensitive.
Must start with a letter or underscore.

<?php$title = "PHP Cheat Sheet";$_count = 10;?>

Constants:

define("PI", 3.14);echo PI;

Data Types

String
Integer
Float (double)
Boolean
Array
Object
NULL
Resource (special variable holding reference to external resources like DB connections)

Escape Characters

Valid in double-quoted strings and heredoc:

\n → newline
\r → carriage return
\t → tab
\\ → backslash
\" → double quote
\$ → dollar sign

⚠️ \e, \v, \f exist but are rarely useful in PHP.

Operators

Arithmetic

+ - * / % **

Assignment

=, +=, -=, *=, /=, %=, .=

Comparison

==, ===, !=, <>, !==, >, <, >=, <=, <=>

(<> is the same as !=) <=> (spaceship operator) returns -1, 0, 1.

Increment / Decrement

++$x, $x++, --$x, $x--

Logical

&&, ||, and, or, xor, !

String

. → concatenation .= → concatenation assignment

Array

+ (union), ==, ===, !=, !==

Conditional Operators

Ternary

$result = ($age >= 18) ? "Adult" : "Minor";

Null Coalescing

$username = $_GET['user'] ?? "Guest";

Control Structures

If / Else / Elseif

if ($x > 10) {    echo "Greater";} elseif ($x == 10) {    echo "Equal";} else {    echo "Smaller";}

Switch

switch ($color) {    case "red":        echo "Stop";        break;    case "green":        echo "Go";        break;    default:        echo "Wait";}

Loops

for ($i=0; $i<5; $i++) { echo $i; } foreach ($arr as $value) { echo $value; }foreach ($arr as $key => $value) { echo "$key => $value"; } while ($x < 5) { $x++; } do { $x++; } while ($x < 5);

Break / Continue are supported.

Functions

function greet($name = "Guest") {    return "Hello, $name";}echo greet("Harry");

Arguments can have default values.
Functions can return values.
PHP supports type declarations:

function add(int $a, int $b): int {    return $a + $b;}

Superglobals

$GLOBALS
$_SERVER
$_GET
$_POST
$_REQUEST
$_FILES (for uploads)
$_COOKIE
$_SESSION
$_ENV

Arrays

$indexed = ["Harry", "Rohan"];$assoc = ["name" => "Harry", "age" => 25];$multi = [  ["Volvo", 100],  ["BMW", 200]];

String Functions

strlen("Harry");           // lengthstr_word_count("Hi all");  // word countstrrev("Harry");           // reversestrpos("Hello world","world"); // positionstr_replace("world","PHP","Hello world"); // replace

File Handling

$file = fopen("test.txt","r");$content = fread($file, filesize("test.txt"));fclose($file); file_put_contents("test.txt","New content");echo file_get_contents("test.txt");

Error Handling

try {    throw new Exception("Error!");} catch (Exception $e) {    echo $e->getMessage();}

OOP in PHP

class Bike {    public $color;    public function __construct($c) { $this->color = $c; }    public function getColor() { return $this->color; }} $myBike = new Bike("red");echo $myBike->getColor();

Access Modifiers: public, private, protected Other OOP Features: inheritance, interfaces, traits, abstract classes, namespaces.

Useful Functions

isset($var) → checks if variable is set
empty($var) → checks if variable is empty
unset($var) → destroys variable
is_array(), is_string(), is_int(), is_null()

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