PHP MCQ Questions

PHP 5.4+ array syntax: $array = [1, 2, 3]; or ['key' => 'value'];. Short syntax. Also array() works. Multiple correct syntaxes.

The empty() function checks if a variable is empty. It returns true for: '', 0, '0', NULL, FALSE, array(), and undefined variables. empty() combines isset() check with falsiness evaluation. Understanding empty() enables concise validation of variable content beyond just existence.

CDATA sections in XML preserve text literally without parsing. Syntax: . Useful for code, scripts, or text with special characters. Prevents XML parsing.

The preg_replace() function performs regex-based search and replace. It supports backreferences for captured groups in replacement. Syntax: preg_replace($pattern, $replacement, $subject). Understanding regex replacement enables complex text transformations.

The hash_equals() function performs timing-attack safe string comparison. Returns boolean. Important for comparing hashes or tokens where timing attacks could reveal information. Always use for security-sensitive comparisons instead of == or ===.

The __construct() magic method is constructor called when creating objects. It initializes object state. Constructor promotion (PHP 8) enables concise property declaration and initialization.

The get_defined_constants() function returns all defined constants as associative array with names as keys. Accepts categorize parameter grouping constants by category (Core, user, extensions). Useful for debugging or inspecting available constants.

The base64_encode() function encodes data to base64 string for safe transmission in text protocols. base64_decode() reverses process. Used for embedding binary data in JSON/XML or email. Not encryption - just encoding for text compatibility.

The __invoke() magic method allows calling objects as functions. Syntax: public function __invoke($args). Called when object used with function syntax: $obj(). Enables callable objects with state. Useful for callbacks, strategies, or function-like objects.

Value of $result = 25 % 6 is 1. Modulo operator returns remainder: 25 divided by 6 equals 4 with remainder 1. Calculation: 6*4=24, 25-24=1. Result: 1. Modulo useful for cycling, even/odd checks, wrapping indices. Always returns integer in PHP.

array_flip() swaps keys and values. Output: Array([a]=>1 [b]=>2 [c]=>3). Original keys become values, values become keys. Useful for reverse lookups.

The $this pseudo-variable references current object instance inside class methods. Access instance properties via $this->property and methods via $this->method(). Not available in static methods. Enables objects to reference their own state and behavior. Fundamental to object-oriented programming.

The mixed type accepts any type. It's default when no type specified. Useful when functions legitimately accept multiple types. Understanding mixed enables explicit any-type acceptance.

The in_array() function checks if value exists in array. Syntax: in_array($needle, $haystack, $strict). The strict parameter enables type checking. Understanding in_array() enables efficient membership testing without loops.

Synchronous cURL calls block execution until response received. Script waits for each request to complete. Default curl_exec() behavior. Use curl_multi for parallel async requests.

Output: A (not B). Loose == compares values after type juggling (123 == '123' true). Strict === requires same type (123 === '123' false).

The simplexml_load_string() function parses XML string into object. Properties represent elements, enabling easy access via object notation. xpath() method enables XPath queries. Simplifies XML processing significantly.

The getrusage() function returns resource usage statistics including user time, system time, page faults. Platform-specific. Useful for performance monitoring and profiling. Returns associative array with usage metrics.

DateInterval specification P0000-10-00T00:01:01 is INVALID format. Correct format: P[years]Y[months]M[days]DT[hours]H[minutes]M[seconds]S. Valid example: P0Y10M0DT0H1M1S means 10 months, 1 minute, 1 second. P prefix required, T separates date and time. Given format has hyphens which are invalid. Proper DateInterval uses ISO 8601 duration format.

PHP 7 multiple class import syntax: use Namespace\{ClassA, ClassB, ClassC}; Group import with curly braces. Example: use App\Models\{User, Product, Order}; Cleaner than separate use statements. Reduces redundancy. Alternative: individual imports: use Namespace\ClassA; use Namespace\ClassB; Group syntax preferred for multiple classes from same namespace.

The ceil() function rounds number up to next integer. Always rounds toward positive infinity. Returns float in PHP (unlike some languages). Useful for pagination calculations or ensuring minimum integer values.

The isset() function determines if a variable is declared and not NULL. Returns true if variable exists and has non-NULL value, false otherwise. Unlike empty() which checks falsy values, isset() only checks existence and NULL status. Safe for checking potentially undefined variables as it doesn't generate warnings. Essential for input validation.

Error 'headers already sent' occurs when output sent before header() call. Causes: whitespace before

The rollBack() method cancels transaction, reverting all changes made since beginTransaction(). Syntax: $pdo->rollBack(). Use in catch blocks when errors occur during transaction, ensuring database consistency.

The unlink() function deletes files. rmdir() removes directories. Understanding file deletion enables cleanup and file management.

echo: multiple parameters, no return. print: one parameter, returns 1. echo faster. Both language constructs. Minimal practical difference.

The array_splice() function removes portion and optionally replaces it. Modifies original array. Syntax: array_splice($array, $offset, $length, $replacement). Returns removed elements. Useful for editing arrays or inserting elements.

The disk_free_space() and disk_total_space() functions report disk space information. Useful for checking available space before operations or displaying storage statistics. Values in bytes.

The strcspn() function returns length of initial segment not containing any specified characters. Opposite of strspn(). Useful for validation or finding first occurrence of forbidden characters.

Value of $total: 2 + 5 * 20 - 6 / 3. Order of operations (PEMDAS): 5*20=100, 6/3=2, then 2+100-2=100. Multiplication and division before addition and subtraction. Result: 100. Use parentheses to override: (2+5)*20 would be different. Understanding operator precedence crucial for correct calculations.

The strcasecmp() function performs case-insensitive string comparison. Like strcmp() but ignores case differences. Returns same values: 0 for equal, <0 or >0 for inequality. Useful for case-insensitive matching.

array_splice($array, $position, 0, [$item]) fastest for insertion. Third parameter 0 means insert without deleting. Handles insertion and re-indexing in one operation.

The closeCursor() method frees resources from result set, allowing new query execution on same statement. Syntax: $stmt->closeCursor(). Useful when not fetching all results before next query. Prevents 'cannot execute while results pending' errors.

memory_get_peak_usage() returns maximum memory used by script. Useful for optimization, finding memory leaks, monitoring resource usage. Returns bytes.

The jdmonthname() function returns month name for Julian Day in specified calendar. Modes control language and abbreviation. Useful for displaying month names from Julian Day calculations.

The sprintf() function returns formatted string using format specifiers (%s, %d, %f). Unlike printf() which outputs, sprintf() returns string. Essential for precise numeric formatting or template-based string generation.

The dot (.) operator concatenates strings in PHP. Syntax: $result = $str1 . $str2. The compound operator .= appends to existing strings: $str .= ' more text'. Unlike JavaScript which uses + for concatenation, PHP reserves + for arithmetic to avoid type confusion. Concatenation creates new strings; original strings remain unchanged.

The '?' is ternary operator for conditional expressions: $result = condition ? true_val : false_val. Also null coalescing: ?? for isset checks. Short conditional syntax.

The exec() method executes SQL statement and returns number of affected rows. Syntax: $count = $pdo->exec($sql). For INSERT/UPDATE/DELETE without parameters. Returns false on error. Don't use for SELECT queries.

The session_start() function initializes or resumes sessions. It must be called before accessing $_SESSION. Sessions store server-side data identified by session ID cookie. Understanding sessions enables maintaining user state across requests.

The Stringable interface (PHP 8.0+) marks classes implementing __toString(). Automatically implemented by classes with __toString(). Useful as type hint for objects convertible to string.

The curl_multi_* functions enable parallel HTTP requests improving performance when making multiple external calls. Significantly faster than sequential requests. Essential for performance-critical integrations.

The correct way to send SMTP email is using the mail() function for basic needs, but production applications should use dedicated libraries like PHPMailer or SwiftMailer/Symfony Mailer. These libraries support SMTP authentication, TLS/SSL encryption, HTML emails, attachments, and proper header handling. Basic syntax: mail($to, $subject, $message, $headers) but libraries prevent injection and provide better error handling.

The highlight_string() function outputs syntax highlighted version of PHP code string. highlight_file() does same for files. Uses color scheme from php.ini or default. Returns highlighted code as string if return parameter true. Useful for code display or documentation.

The gc_disable() and gc_enable() functions control garbage collector. Disabling can improve performance in specific scenarios like batch processing. Memory usage may increase. Re-enable when done.

Class syntax: class ClassName { properties; methods; }. Can include visibility modifiers (public, private, protected), static members, constants (const NAME = value), constructor (__construct), destructor (__destruct), inheritance (extends), interfaces (implements). Example: class User { public $name; public function getName() { return $this->name; } }

Output: 'Your favorite color is green!'. Switch statement matches $favcolor value against cases. Finds match at case 'green', executes that block, break prevents fall-through to default. Switch uses loose comparison (==). Cases evaluated top-to-bottom until match found. Default executes if no match. Break statements essential to prevent fall-through.

Correct code: printf('#%02x%02x%02x', $r, $g, $b); or sprintf('#%02x%02x%02x', $r, $g, $b); or dechex() for each. %02x formats as 2-digit lowercase hexadecimal, padding with zero. 255 becomes ff, 0 becomes 00. Result: #ff0000 (red). sprintf returns string, printf outputs directly.

The session_destroy() function destroys all session data. It doesn't unset $_SESSION variables or delete the session cookie. Complete session cleanup requires unsetting $_SESSION and deleting the cookie separately. Understanding session destruction enables proper logout functionality.

Correct: $a++; or $a += 1; or $a = $a + 1;. Multiple valid increment methods. ++ operator most concise.