PHP Cheat Sheet — Syntax, Arrays, and Common Patterns

<?php
// Variables start with $
$name = "Alice";
$age = 30;
$price = 19.99;
$active = true;
$nothing = null;
// Type checking
gettype($name);     // “string”
is_string($name);   // true
is_int($age);       // true
isset($name);       // true (exists and not null)
empty($name);       // false
// Type casting
$num = (int) “42”;
$str = (string) 42;
$float = (float) “3.14”;
// Constants
define(‘MAX_SIZE’, 100);
const APP_NAME = ‘MyApp’;
// String interpolation
echo “Hello $name”;
echo “Hello {$name}!”;
echo ‘No $interpolation here’;  // Single quotes = literal

strlen($str)                    // Length
strtolower($str)                // Lowercase
strtoupper($str)                // Uppercase
trim($str)                      // Remove whitespace
str_contains($str, "hello")     // Contains (PHP 8+)
str_starts_with($str, "Hello")  // Starts with (PHP 8+)
str_replace("old", "new", $str) // Replace
substr($str, 0, 5)              // Substring
explode(",", $str)              // Split → array
implode(", ", $arr)             // Join array → string
sprintf("Hello %s, age %d", $name, $age)

// Indexed array
$fruits = ["apple", "banana", "cherry"];
$fruits[] = "date";          // Append
$fruits[0];                  // "apple"
count($fruits);              // 4
// Associative array (like a dict/map)
$user = [
“name” => “Alice”,
“email” => “alice@example.com”,
“age” => 30,
];
$user[“name”];               // “Alice”
$user[“role”] = “admin”;     // Add key
// Check key exists
array_key_exists(“name”, $user);  // true
isset($user[“name”]);             // true
// Common functions
sort($fruits);                    // Sort (modifies in place)
array_push($fruits, “elderberry”);
array_pop($fruits);               // Remove last
in_array(“apple”, $fruits);       // Contains
array_merge($arr1, $arr2);        // Merge
array_keys($user);                // [“name”, “email”, “age”]
array_values($user);              // [“Alice”, “alice@…”, 30]
// Array destructuring (PHP 7.1+)
[$first, $second] = $fruits;
[“name” => $name, “age” => $age] = $user;

$nums = [1, 2, 3, 4, 5];
// Map
$doubled = array_map(fn($n) => $n * 2, $nums);
// [2, 4, 6, 8, 10]
// Filter
$evens = array_filter($nums, fn($n) => $n % 2 === 0);
// [2, 4]
// Reduce
$sum = array_reduce($nums, fn($carry, $n) => $carry + $n, 0);
// 15
// Foreach
foreach ($user as $key => $value) {
echo “$key: $value\n”;
}

// Basic function
function greet(string $name): string {
    return "Hello, $name!";
}
// Default parameters
function connect(string $host = “localhost”, int $port = 3306): void {
// …
}
// Nullable types
function findUser(int $id): ?User {
return null; // Can return User or null
}
// Arrow functions (PHP 7.4+)
$double = fn($x) => $x * 2;
// Spread operator
function sum(int …$nums): int {
return array_sum($nums);
}
sum(1, 2, 3, 4); // 10
// Named arguments (PHP 8+)
connect(port: 5432, host: “db.example.com”);

class User {
    // Constructor promotion (PHP 8+)
    public function __construct(
        private string $name,
        private string $email,
        private int $age = 0,
    ) {}
public function getName(): string {
    return $this->name;
}
}
$user = new User(“Alice”, “alice@example.com”, 30);
// Interface
interface Printable {
public function toString(): string;
}
// Enum (PHP 8.1+)
enum Status: string {
case Active = ‘active’;
case Inactive = ‘inactive’;
}
// Match expression (PHP 8+)
$label = match($status) {
Status::Active => ‘Active’,
Status::Inactive => ‘Inactive’,
};

try {
    $result = riskyOperation();
} catch (InvalidArgumentException $e) {
    echo "Invalid: " . $e->getMessage();
} catch (Exception $e) {
    echo "Error: " . $e->getMessage();
} finally {
    // Always runs
}
// Null coalescing
$name = $user[“name”] ?? “Anonymous”;
// Nullsafe operator (PHP 8+)
$city = $user?->getAddress()?->getCity();