Php Cheatsheet

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");           // length
str_word_count("Hi all");  // word count
strrev("Harry");           // reverse
strpos("Hello world","world"); // position
str_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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