PHP MCQ Questions

Readonly properties (PHP 8.1+) can only be initialized once and never modified. Declared with readonly keyword. Entire classes can be readonly (PHP 8.2+) making all properties readonly. Enables immutable objects preventing accidental modifications.

The strlen() function returns string length in bytes. For multibyte strings (UTF-8), use mb_strlen() instead, which counts characters correctly. Understanding the difference prevents incorrect length calculations with international characters.

Controller in MVC (Model-View-Controller) handles user input, processes requests, orchestrates model and view. Receives user actions (form submissions, clicks), calls appropriate model methods for data operations, selects view to display, passes data to view. Acts as intermediary between model (data/business logic) and view (presentation). Implements application flow control.

The instanceof operator checks if object is instance of class or implements interface. Returns boolean. Understanding instanceof enables safe type checking before operations.

The extends keyword creates inheritance relationship, allowing child class to inherit parent's non-private properties and methods. PHP supports single inheritance only. Syntax: class Child extends Parent. Override methods using parent:: to call parent version. Enables code reuse and polymorphism through inheritance hierarchies.

Key differences: GET appends data to URL (visible, limited size ~2KB), POST sends data in request body (invisible, larger size). GET cached/bookmarked, POST not. GET for retrieval, POST for submission/modification. GET idempotent, POST not necessarily. GET less secure (data in URL/history/logs), POST more secure. Use GET for read, POST for write operations.

The umask() function sets default file permission mask affecting newly created files. Returns previous mask. Important for security ensuring files created with appropriate permissions.

The cal_from_jd() and cal_to_jd() functions convert between Julian Day Count and calendar dates. JD enables date arithmetic across calendars. Useful for astronomical or historical date calculations.

Output: 5\n3\n4 (with actual newlines if interpreted). Function passes by reference (&$arg), so modifications affect original. First call: returns 3, $a becomes 4. Second call: returns 4, $a becomes 5. Echo outputs $a (5), $b (3), $c (4) separated by literal \n strings (or newlines if in actual execution).

The mb_strtoupper() function converts multibyte string to uppercase respecting encoding. Unlike strtoupper() which only handles ASCII, mb_strtoupper() works with international characters. mb_strtolower() does reverse.

The json_encode() function converts PHP values into JSON strings. Options parameter controls encoding behavior: JSON_PRETTY_PRINT for readability, JSON_UNESCAPED_UNICODE for international characters, JSON_NUMERIC_CHECK for numeric string conversion. Returns false on error; use json_last_error() for debugging. Critical for APIs and JavaScript communication.

The preferred if statement style uses braces even for single statements and meaningful variable names. For example, if ($userIsActive) { processUser(); } is better than if ($a) processUser();. This prevents errors when adding statements later, improves readability, and follows PSR standards. Always use braces and descriptive variables for maintainability.

The __get() magic method intercepts property access to undefined or inaccessible properties. Syntax: public function __get($name). Enables dynamic property access, lazy loading, or property virtualization. Pair with __set() for write access. Useful for property overloading and computed properties.

The next() function advances internal array pointer to next element and returns its value. Returns false when reaching end. Part of array traversal functions. Useful for manual iteration when foreach isn't suitable or when needing pointer control.

The usort() function sorts array using user-defined comparison callback. The callback should return -1, 0, or 1. It enables custom sorting logic beyond simple value comparison.

NULL is absence of value, variable exists but has no value. Unset variables are NULL. is_null() tests for NULL. Empty is broader concept: empty string '', 0, '0', false, null, empty array [] all considered empty. empty() function returns true for NULL plus other falsy values. NULL is specific type, empty is state.

The iconv() function converts string between character encodings. More widely available than mb_convert_encoding(). Syntax: iconv($from, $to, $string). Adding '//TRANSLIT' or '//IGNORE' to $to parameter controls invalid character handling.

The file_put_contents() function writes string to file, creating or overwriting it. FILE_APPEND flag appends instead. Understanding file writing enables data persistence.

The array_reduce() function reduces array to single value by iteratively applying callback. Callback receives carry value and current element, returning new carry. Syntax: array_reduce($array, $callback, $initial). Perfect for summing, concatenating, or aggregating array values into single result through functional programming approach.

Missing: no session_start() before session functions. Add session_start() at beginning. Headers already sent if any output before header(). Proper sequence matters.

The nl_langinfo() function returns locale-specific information for various categories. More detailed than localeconv() for cultural conventions. Platform-specific. Useful for internationalization.

The bindColumn() method binds result column to variable. Each fetch() updates bound variables. Syntax: $stmt->bindColumn(1, $var). Useful for processing results without array access, but fetch() with FETCH_ASSOC is more common.

The correct way to join strings in PHP is using the dot (.) operator: $str = 'abcdef' . 'ghi';. The plus (+) operator is for arithmetic addition, not string concatenation. Using + with strings attempts numeric conversion. The .= operator appends to existing strings. Proper concatenation prevents errors and unexpected results.

The http_build_query() function builds URL-encoded query string from associative array. Handles encoding automatically. Useful for constructing URLs programmatically or preparing API requests with parameters.

Object-oriented associative array style: $result->fetch_assoc() for mysqli returns associative array with column names as keys. $stmt->fetchAll(PDO::FETCH_ASSOC) for PDO. Access via column names: $row['column_name']. OOP syntax uses arrow operator on result object. Returns one row per fetch call.

Procedural associative array style: mysqli_fetch_assoc($result) returns associative array with column names as keys. Access: $row['column_name']. Procedural functions take result resource as parameter. Alternative: mysqli_fetch_array($result, MYSQLI_ASSOC). Returns one row per call, NULL when no more rows.

The SplDoublyLinkedList class implements doubly-linked list with stack and queue operations. SplStack and SplQueue extend it. Useful for implementing specific data structures.

The var_dump() function displays detailed information about variables including type, length, and nested structure. Unlike print_r(), shows types explicitly. Essential debugging tool for understanding variable content and structure. Output not meant for production display.

ucwords('ThiS iS a SenTEnCe') outputs 'ThiS IS A SenTEnCe'. Capitalizes first letter of each word, preserves rest. Word-level capitalization.

Use output buffering: ob_start(); var_dump($var); $dump = ob_get_clean(); Captures var_dump output into string variable. Useful for logging or processing.

Without seeing the snippet, cannot determine output. The ! (NOT) operator inverts boolean: !true becomes false, !false becomes true. !(expression) negates result. Applied to non-boolean values: converts to boolean first then inverts. Example: !0 is true, !5 is false. Understanding negation essential for conditional logic.

The gc_collect_cycles() function forces garbage collection cycle. PHP automatically garbage collects circular references but manual collection can free memory immediately. gc_enabled() checks if garbage collector enabled.

The class_uses() function returns array of traits used by class. Includes traits used by parent classes and traits. Useful for checking trait composition.

$_REQUEST is superglobal combining $_GET, $_POST, and $_COOKIE arrays. Contains data from all three sources. Order controlled by variables_order directive. Security concern: unclear data source. Better practice: use specific superglobals ($_GET, $_POST) for clarity and security. Avoid $_REQUEST when possible to know exact data origin.

Public members are accessible everywhere, protected members only within the class and its subclasses, private members only within the defining class itself. Public enables external access, protected enables inheritance while hiding from outside, private ensures encapsulation. Proper visibility controls access, enforces encapsulation, and prevents unintended modifications.

The SplObjectStorage class implements object set or object-to-data map. Objects are keys, can store associated data. Useful for tracking objects or implementing observer pattern.

The compact() function creates associative array from variable names and their values. Variable names are strings that become keys. Syntax: compact('var1', 'var2'). Useful for passing multiple variables to views, templates, or functions as single array. Opposite operation is extract().

The array_combine() function creates array using one array for keys and another for values. Arrays must have equal length. If duplicate values in keys array, later overwrites. Useful for pairing separate key and value lists into associative array.

The htmlspecialchars() function converts special characters to HTML entities preventing XSS attacks. Always use when outputting user data to HTML. Converts <, >, &, ', " by default. Critical security function for web applications.

The printf() and vprintf() functions output formatted strings directly instead of returning. printf() uses variable arguments, vprintf() uses array. Useful for formatted output without intermediate variables.

The array_unique() function removes duplicate values from array. It uses value comparison, preserving first occurrence. Understanding uniqueness checking enables eliminating redundant array elements.

The preg_match() function performs regular expression matching, returning 1 if pattern matches, 0 if not, or false on error. Syntax: preg_match($pattern, $subject, $matches). The $matches array captures matched groups. For global matching, use preg_match_all(). Essential for complex pattern matching, validation, and text extraction.

Code contains syntax error: 'printf(foods var export food true)' is invalid PHP syntax. Should be: var_export($food, true) or printf with proper format. Cannot determine output due to syntax error. Correct syntax might be: print_r($food) or var_export($food, true) or echo var_export($food, true). Tests recognition of invalid PHP syntax.

The try-catch block handles exceptions. Code in try block executes, and if exception thrown, matching catch block handles it. finally block executes regardless. Understanding exception handling enables robust error management.

The array_reduce() function iteratively reduces array to single value using callback. The callback receives accumulator and current value. Syntax: array_reduce($array, $callback, $initial). It's perfect for summing, multiplying, or aggregating array values functionally.

The abs() function returns absolute value of number (removes sign). Works with integers and floats. Returns same type as input. Simple but essential for distance calculations, magnitude comparisons, or ensuring positive values.

The header() function sends raw HTTP headers to browser. Must be called before any output (whitespace, HTML, echo). Common uses: header('Location: page.php') for redirects, header('Content-Type: application/json') for API responses. Headers control caching, authentication, CORS, and content types. Understanding HTTP headers is crucial for web development.

The $_COOKIE superglobal accesses cookie values sent by client. Cookies are user-controlled so always validate and sanitize. Never trust cookie data for security decisions. Use signed cookies or server-side sessions for sensitive data.

Access static properties/methods: ClassName::$property or ClassName::method(). Within class, use self::$property or static::$property (late static binding). Example: Utilis::$numstudent or self::$numstudent inside class. Static members belong to class, not instances. No $this in static context. Use :: (scope resolution operator) for access.

The explode() function splits strings into arrays based on delimiter. Syntax: explode($delimiter, $string, $limit). Limit parameter controls maximum array elements. Example: explode(',', 'a,b,c') returns ['a','b','c']. Opposite of implode(). Essential for parsing CSV, splitting sentences, or processing delimited data.