PHP Fundamentals Cheatsheet

PHP Syntax

PHP Tags

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<?php echo "Standard tag"; ?>
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<?= "Short echo tag" ?>

Statement Rules

Every statement ends with a semicolon (;)
Variables are case-sensitive ($name ≠ $Name)
Functions/keywords are case-insensitive (echo = ECHO)

Comments

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// Single-line comment
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# Also single-line
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/* Multi-line
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   comment */
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/** PHPDoc comment */

Variables

Declaration

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$name = "John";       // String
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$age = 25;            // Integer
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$price = 19.99;       // Float
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$isActive = true;     // Boolean
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$items = [1, 2, 3];   // Array

Naming Rules

Must start with $ followed by letter or underscore
Can contain letters, numbers, underscores
Cannot start with a number or contain hyphens

Scope

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$global = "accessible everywhere with global keyword";
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function example() {
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    global $global;           // Access global variable
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    $local = "only here";     // Local to function
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    static $count = 0;        // Persists between calls
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    $count++;
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}

References

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$a = 5;
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$b = &$a;    // $b references $a
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$b = 10;     // $a is now also 10

Constants

Defining Constants

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// Using define() - can be used anywhere
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define('SITE_NAME', 'My Website');
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define('COLORS', ['red', 'green', 'blue']);  // PHP 7+
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// Using const - must be at top level
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const MAX_USERS = 100;
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const TAX_RATE = 0.08;

Checking & Accessing

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if (defined('SITE_NAME')) {
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    echo SITE_NAME;
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}

Magic Constants

Constant	Description
`__FILE__`	Full path of current file
`__DIR__`	Directory of current file
`__LINE__`	Current line number
`__FUNCTION__`	Current function name
`__CLASS__`	Current class name
`__METHOD__`	Current class method

Arrays

Indexed Arrays

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$fruits = ["apple", "banana", "orange"];
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echo $fruits[0];       // apple
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$fruits[] = "grape";   // Add to end

Associative Arrays

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$user = [
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    "name" => "John",
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    "age" => 30,
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    "email" => "john@example.com"
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];
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echo $user["name"];    // John

Multidimensional Arrays

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$products = [
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    "laptop" => ["price" => 800, "qty" => 5],
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    "mouse" => ["price" => 25, "qty" => 20]
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];
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echo $products["laptop"]["price"];  // 800

Looping

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// Indexed
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foreach ($fruits as $fruit) {
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    echo $fruit;
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}
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// Associative (key => value)
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foreach ($user as $key => $value) {
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    echo "$key: $value";
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}

Common Array Functions

Function	Description
`count($arr)`	Get array length
`in_array($val, $arr)`	Check if value exists
`array_push($arr, $val)`	Add to end
`array_pop($arr)`	Remove from end
`array_merge($a, $b)`	Merge arrays
`array_keys($arr)`	Get all keys
`array_values($arr)`	Get all values
`sort($arr)`	Sort array

Strings

Single vs Double Quotes (Single-line)

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$name = "PHP";
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// Single quotes: literal (no parsing)
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echo 'Hello $name';      // Hello $name
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// Double quotes: variable interpolation
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echo "Hello $name";      // Hello PHP
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echo "Hello {$name}!";   // Hello PHP! (explicit syntax)

Heredoc & Nowdoc (Multi-line Strings)

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// Heredoc - parses variables (like double quotes)
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$html = <<<HTML
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<h1>Welcome, $name!</h1>
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<p>This can span multiple lines</p>
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HTML;
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// Nowdoc - literal (like single quotes)
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$js = <<<'JS'
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console.log('$name not parsed');
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// Also supports multiple lines
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JS;

Concatenation

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$greeting = "Hello" . " " . "World";  // Hello World
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$greeting .= "!";                      // Hello World!

Common String Functions

Function	Description
`strlen($str)`	String length
`strtoupper($str)`	Convert to uppercase
`strtolower($str)`	Convert to lowercase
`substr($str, 0, 5)`	Extract substring
`str_replace("a", "b", $str)`	Replace text
`trim($str)`	Remove whitespace
`explode(",", $str)`	Split string to array
`implode(",", $arr)`	Join array to string

Functions

Basic Declaration

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function greet($name) {
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    return "Hello, $name!";
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}
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echo greet("John");  // Hello, John!

Default Parameters

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function greet($name = "Guest", $greeting = "Hello") {
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    return "$greeting, $name!";
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}
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greet();              // Hello, Guest!
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greet("John");        // Hello, John!
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greet("John", "Hi");  // Hi, John!

Pass by Reference

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function increment(&$value) {
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    $value++;
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}
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$num = 5;
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increment($num);
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echo $num;  // 6

Variadic Parameters

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function sum(...$numbers) {
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    return array_sum($numbers);
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}
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echo sum(1, 2, 3, 4);  // 10

Type Hints (PHP 7+)

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// Parameter type hints
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function greet(string $name): void {
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    echo "Hello, $name!";
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}
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// Multiple types with return type
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function add(int $a, int $b): int {
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    return $a + $b;
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}
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// Nullable types (PHP 7.1+)
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function findUser(?int $id): ?array {
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    return $id ? ['id' => $id] : null;
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}
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// Union types (PHP 8+)
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function process(int|float $value): int|float {
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    return $value * 2;
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}

Common Type Hints: string, int, float, bool, array, object, mixed, void, null

Named Arguments (PHP 8+)

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function createUser($name, $email, $age = null) { }
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createUser(name: "John", email: "john@test.com");

Quick Reference Tables

Type Checking Functions

Function	Checks for
`is_string($var)`	String
`is_int($var)`	Integer
`is_float($var)`	Float
`is_bool($var)`	Boolean
`is_array($var)`	Array
`is_null($var)`	Null
`isset($var)`	Variable exists and not null
`empty($var)`	Empty value

Math Functions

Function	Description
`abs($n)`	Absolute value
`round($n)`	Round number
`ceil($n)`	Round up
`floor($n)`	Round down
`max($a, $b)`	Maximum value
`min($a, $b)`	Minimum value
`rand($min, $max)`	Random number

Date Functions

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echo date('Y-m-d');          // 2024-01-15
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echo date('H:i:s');          // 14:30:00
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echo time();                 // Unix timestamp
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echo strtotime('+1 week');   // Timestamp in 1 week