PHP MCQ

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PHP is a recursive acronym: PHP: Hypertext Preprocessor. It is a server-side scripting language.

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<?php is the standard opening tag. The short tag <? requires short_open_tag=On and is not recommended for portability.

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PHP variables start with a $ sign followed by the name. PHP is dynamically typed — no type declaration is needed.

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echo and print both output text. echo can output multiple comma-separated strings; print returns 1 (a value).

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PHP supports // and # for single-line comments and /* ... */ for multi-line comments.

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The dot (.) operator concatenates strings in PHP. $str = "Hello" . " World";

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PHP supports both array() constructor and the shorthand [] syntax (PHP 5.4+).

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isset($var) returns true if $var is declared and not null. It returns false for null values and undefined variables.

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0 == "0" is true (type juggling). 0 === "0" is false (different types: int vs string).

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PHP functions are declared with the function keyword followed by the function name and parentheses.

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count($array) returns the number of elements. strlen() returns string length.

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$_POST contains data submitted via HTTP POST. $_GET contains URL query parameters. $_REQUEST contains both.

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PHP classes are defined with class MyClass { } and instantiated with new MyClass().

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$this refers to the current object instance inside non-static class methods.

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PHP uses extends for class inheritance and implements for interfaces.

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__construct() initializes object properties when new MyClass() is called.

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include gives a warning but continues if the file is not found. require gives a fatal error and halts. include_once and require_once prevent multiple inclusions.

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var_dump() outputs the type and value. For true: bool(true). It's more informative than echo or print_r.

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Associative array values are accessed with $arr['key'] or $arr["key"].

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$name = $_GET['name'] ?? 'Anonymous' returns $_GET['name'] if set, otherwise 'Anonymous'. Added in PHP 7.

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Both append to the end of an array. $arr[] = $val is preferred for single elements; array_push($arr, $a, $b) for multiple at once.

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Interfaces declare method signatures without implementations. A class implements an interface with the implements keyword.

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PHP functions have their own scope. To access a global variable inside a function, use the global keyword or $GLOBALS superglobal.

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intval("42") or (int)"42" both return 42. intval() allows specifying a base (e.g., intval("0xFF", 16)).

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empty($var) returns true for "", 0, "0", null, false, [], 0.0. It suppresses errors for undefined variables.

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Sessions store data server-side across requests. Start with session_start() and store data in $_SESSION. A session ID is stored in a cookie.

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The :: (Paamayim Nekudotayim) operator calls static methods: MyClass::method(). static:: is for late static binding.

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foreach ($array as $key => $value) iterates over arrays and objects. foreach ($array as $value) skips the key.

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$a <=> $b returns -1 if $a < $b, 0 if equal, 1 if $a > $b. Added in PHP 7, useful for usort() callbacks.

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htmlspecialchars() converts <, >, &, ", ' to HTML entities, preventing cross-site scripting (XSS) attacks.

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The ternary operator $result = $condition ? "yes" : "no" evaluates to $x if true, $y if false.

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Traits allow horizontal code reuse without inheritance. use MyTrait; inside a class includes the trait's methods.

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unset($var) destroys the variable. Inside a function, it only affects the local variable unless passed by reference.

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sort() sorts by value and re-indexes keys. asort() preserves keys. ksort() sorts by key. rsort() sorts in descending order.

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PDO provides a consistent interface for accessing multiple databases (MySQL, PostgreSQL, SQLite, etc.) and supports prepared statements.

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print_r() displays arrays and objects in a readable format. Pass true as the second argument to return the output as a string instead of printing it.

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PHP automatically converts types in loose comparisons. "1" == 1 is true because PHP juggles "1" to integer 1. Use === to avoid this.

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With strict_types=1 at the top of a file, passing a string to a function expecting int throws a TypeError instead of coercing.

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Magic methods like __construct, __get, __set, __toString, __invoke are called automatically by PHP in specific contexts.

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str_replace("cat", "dog", "the cat sat") returns "the dog sat". It is case-sensitive; str_ireplace() is case-insensitive.

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Abstract classes can provide partial implementations and state. A class can only extend one abstract class but implement multiple interfaces.

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$fn = function($x) use ($factor) { return $x * $factor; }; captures $factor by value. use (&$var) captures by reference.

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self:: refers to the defining class. static:: refers to the called class (late binding), enabling proper polymorphism in static methods.

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DI passes dependencies (e.g., a database connection) via constructors or methods instead of using new inside the class, enabling mocking in tests.

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function gen() { yield 1; yield 2; } creates a Generator object. Values are produced on-demand, saving memory for large sequences.

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array_map(fn($x) => $x * 2, [1,2,3]) returns [2,4,6]. For filtering use array_filter(); for reducing use array_reduce().

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array_slice(array: $arr, offset: 0, length: 3) uses named args. They improve readability and allow skipping middle optional parameters.

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match($val) { 1 => "one", 2 => "two" } uses === comparison, throws UnhandledMatchError for no match, and has no fall-through.

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Fibers allow suspending and resuming execution at any point, enabling cooperative multitasking and async-like patterns without callback hell.

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PHP 8 union types (int|string) allow parameters or returns to be one of the listed types. PHP 8.2 adds intersection types (Iterator&Countable).

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#[Route("/home")] is an attribute. Unlike docblock annotations, attributes are native PHP syntax readable via Reflection, enabling frameworks to use them natively.

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$user?->getAddress()?->getCity() returns null if $user or getAddress() is null, avoiding multiple isset() checks. Added in PHP 8.

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The _once variants track included files to prevent duplicate inclusion. The difference between include and require is error behavior.

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PSR (PHP Standards Recommendation) guidelines include PSR-4 (autoloading), PSR-7 (HTTP messages), and PSR-12 (coding style).

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PSR-4 maps App\ to src/. Composer's autoloader implements it; class App\Controllers\HomeController maps to src/Controllers/HomeController.php.

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switch uses loose == comparison and allows accidental fall-through. match uses ===, must handle all cases (or have default), and can be assigned directly.

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public readonly string $name allows setting $name once (usually in __construct). Any subsequent write throws Error.

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function f(...$args) collects variadic args. f(...$array) unpacks the array as individual arguments.

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[1,2] + [3,4,5] = [1,2,5] (+ keeps first values for existing keys). array_merge([1,2],[3,4,5]) = [1,2,3,4,5] (appends).

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$copy = clone $original; creates a shallow copy. Define __clone() to perform deep copies of nested objects.

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enum Status { case Active; case Inactive; } Pure enums have no value. Backed enums: enum Status: string { case Active = 'active'; }.

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SPL provides SplStack, SplQueue, SplDoublyLinkedList, ArrayObject, RecursiveIteratorIterator, and more.

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Without strict_types, PHP coerces "5" to 5 when an int is expected. With strict_types=1, this throws a TypeError.

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Composer manages project dependencies via composer.json, installs packages into vendor/, and generates the PSR-4 autoloader.

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fn($x) => $x * $factor automatically captures $factor by value without use. Added in PHP 7.4.

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The intl extension wraps ICU library functionality: NumberFormatter, DateFormatter, Collator, MessageFormatter for locale-sensitive operations.

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ReflectionClass, ReflectionMethod, ReflectionProperty allow inspecting code structure at runtime — used by DI containers, ORMs, and testing frameworks.

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Fix session fixation by calling session_regenerate_id(true) after login to assign a new session ID, invalidating any pre-login ID set by an attacker.

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IoC containers auto-wire dependencies by inspecting constructor type hints via Reflection. Laravel's App::make() and type-hint injection in controllers use this.

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setcookie("name", "value", time()+3600) is equivalent to header("Set-Cookie: name=value; ..."). Both require no output before they are called.

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array_walk($arr, function(&$val, $key) { $val = strtoupper($val); }) modifies values in place. Return value is bool, not the modified array.

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$name = "Alice"; $age = 30; compact("name", "age") returns ["name" => "Alice", "age" => 30]. The inverse is extract().

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final public function calculate() in a parent class prevents child classes from overriding it, enforcing the algorithm's behavior.

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PHP 5.3+ generates a strict warning: abstract static methods are logically problematic since static methods cannot be truly overridden (no dynamic dispatch).

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ob_start(); echo "Hello"; $content = ob_get_clean(); captures "Hello" without sending it. Used for template engines and testing.

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Unlike DateTime::modify() which mutates, DateTimeImmutable::modify() returns a new object. Prevents accidental mutation in code that passes dates around.

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PHP 8.1 allows array unpacking with string keys: [...$defaults, ...$overrides]. The splat creates a merged array with later values overwriting earlier ones.

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$fn = strlen(...) is equivalent to Closure::fromCallable("strlen"). Works for functions, methods, static methods: $fn = $obj->method(...).

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Generators are limited to yielding at explicit yield statements. Fibers can suspend at any point in nested function calls, enabling deeper coroutine patterns.

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serialize() preserves PHP objects (class name + state) for PHP-to-PHP transfer. json_encode() is portable, human-readable, but loses PHP class information.

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OPcache stores compiled PHP bytecode in shared memory. Subsequent requests skip parsing/compilation, dramatically reducing response time.

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PHP Fibers (8.1) are stackful coroutines with Fiber::suspend(). Async frameworks like ReactPHP use Fibers as the foundation for async/await syntax.

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PHP 8's JIT (tracing and function modes) compiles frequently executed code to native x86 machine code, improving CPU-intensive workloads.

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PHP objects are passed by handle. $b = $a means both point to the same object. Modifying $b modifies the same object. Use clone $a for an independent copy.

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WeakMap allows attaching data to objects without preventing their garbage collection. Useful for caching per-object metadata without memory leaks.

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function f(Iterator&Countable $x) requires $x to implement both Iterator and Countable. Intersection types are the dual of union types.

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$b = $a copies the reference count. When $b is modified, PHP separates them (copy-on-write). This avoids expensive copies when arrays are only read.

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A zval (Zend value) is the C structure holding any PHP value: type flag, reference count, and a union for the value. PHP 7 redesigned zvals to reduce memory usage.

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Named arguments bind by parameter name, so renaming a parameter is a breaking change for any callers relying on the old name.

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Psalm and PHPStan analyze PHP code statically, catching type mismatches and null pointer bugs that PHP's runtime would only catch when that code path is executed.

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Use ini_set("memory_limit", "512M") for scripts requiring more memory. Generators and lazy iterators avoid loading entire datasets into memory.

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Custom session handlers implement open, close, read, write, destroy, gc methods. Used for distributed session storage in horizontally-scaled PHP applications.

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Using SplStack enforces LIFO semantics. SplMinHeap gives O(log n) min-element access. They communicate intent and enforce correctness over generic arrays.

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With preloading, frameworks precompile their core files. Workers inherit the preloaded code without parsing overhead. Requires FPM restart to update preloaded files.

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function f(string $name, ...$args): named args like name: "x" work, but variadic ...$args cannot be individually targeted by name.

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match($val) without a default that covers all cases throws UnhandledMatchError when no arm matches. This is intentional — use default to handle unexpected values explicitly.

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function redirect(string $url): never { header("Location: $url"); exit(); } — never communicates to static analyzers and the reader that this function never returns.

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class Logger { function __call($name, $args) { log($name); return $this->wrapped->$name(...$args); } } wraps any object adding logging without modifying it.

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PHP type juggling: "0" is falsy (empty-string-like in bool context), so "0" == false is true. But (bool)"0" === false. This asymmetry is a known PHP gotcha, fixed with ===.

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PHP's runtime types are enforced by declare(strict_types=1) and type declarations. Generic types (Collection<User>) are only in docblocks, analyzed by Psalm/PHPStan, not enforced at runtime.