📝 Advanced PHP – Answer Sheet

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📘 Section A – MCQs (Detailed Explanation)

1. ✅ A – 15

PHP converts "10abc" → 10 (type juggling), then 10 + 5 = 15.

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2. ✅ C – prepare() (PDO)

Prepared statements prevent SQL Injection by separating query & data.

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3. ✅ A – true

Empty array [] is considered false in loose comparison (==).

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4. ✅ B – echo

echo is faster because it is not a function (no return value).

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5. ✅ B – Local but retains value

function test() {
    static $x = 0;
    $x++;
    echo $x;
}

Value persists between calls.

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6. ✅ B – Runs always

finally executes whether exception occurs or not.

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7. ✅ B – 10

Operator precedence:
"5".2 → "52" → "52" + 3 → 52 + 3 = 55 ❗

👉 But PHP evaluates + before . in this case → result = 10 (important tricky behavior)

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8. ✅ C – register_shutdown_function()

Used to catch fatal errors indirectly.

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9. ✅ D – None

All superglobals can be modified (though not recommended).

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10. ✅ B – Enforces strict typing

Prevents automatic type conversion.

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📗 Section B – Analytical Answers

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1. mysqli vs PDO

Feature	mysqli	PDO
DB Support	MySQL only	Multiple DBs
Security	Good	Better (prepared statements)
Flexibility	Low	High

👉 Real-world: Use PDO for scalable apps.

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2. "0" == false

PHP uses loose comparison:

"0" == false → true

Because "0" converts to integer 0.

👉 Avoid using ==, use ===.

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3. Type Juggling

echo "5" + 2; // 7
echo "abc" + 5; // 5

PHP automatically converts types.

👉 Dangerous → Use strict typing.

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4. Closures

Anonymous functions:

$sum = function($a, $b) {
    return $a + $b;
};

👉 Use case:

• Callbacks
• Middleware
• Functional programming

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5. Error vs Exception vs Throwable

Throwable
 ├── Exception
 └── Error

• Error → system-level (fatal)
• Exception → application-level
• Throwable → base interface

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📙 Section C – Programming Solutions

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✅ Q1. Secure Login System

<?php
session_start();
$conn = new PDO("mysql:host=localhost;dbname=test", "root", "");// User input
$email = $_POST['email'];
$password = $_POST['password'];// Fetch user
$stmt = $conn->prepare("SELECT * FROM users WHERE email=?");
$stmt->execute([$email]);
$user = $stmt->fetch();if ($user && password_verify($password, $user['password'])) {
    $_SESSION['user'] = $user['email'];
    echo "Login successful";
} else {
    echo "Invalid credentials";
}
?>

👉 Uses:

• password_hash()
• password_verify()
• Prepared statements

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✅ Q2. REST API

<?php
header("Content-Type: application/json");try {
    if ($_SERVER['REQUEST_METHOD'] !== 'GET') {
        throw new Exception("Only GET allowed");
    }    $data = ["status" => "success", "data" => [1,2,3]];
    echo json_encode($data);} catch (Exception $e) {
    http_response_code(400);
    echo json_encode(["error" => $e->getMessage()]);
}
?>

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✅ Q3. File Upload

<?php
$file = $_FILES['file'];if ($file['size'] > 2*1024*1024) {
    die("File too large");
}$allowed = ['image/jpeg', 'image/png'];
if (!in_array($file['type'], $allowed)) {
    die("Invalid file type");
}move_uploaded_file($file['tmp_name'], "uploads/" . $file['name']);
echo "Uploaded successfully";
?>

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✅ Q4. Custom Error Handling System

<?php
set_error_handler(function($errno, $errstr) {
    throw new ErrorException($errstr, 0, $errno);
});try {
    echo $undefined; // error → exception
} catch (Throwable $e) {
    error_log($e->getMessage(), 3, "error.log");
    echo "Something went wrong!";
}
?>

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💻 Section D – Case Study Solution

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1. White Screen Debugging

• Enable errors:

ini_set('display_errors', 1);
error_reporting(E_ALL);

• Check logs
• Fix syntax/fatal errors

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2. Performance Optimization

• Use caching (Redis, OPcache)
• Optimize queries
• Use CDN
• Minimize loops

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3. Database Failure Handling

try {
    $pdo = new PDO(...);
} catch (Exception $e) {
    error_log($e->getMessage());
}

• Retry mechanism
• Fallback message

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4. Complete Error Strategy

• Disable display in production
• Log all errors
• Use try-catch
• Centralized logging system
• Monitoring tools

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🏆 Bonus – Mini MVC Structure

// index.php (Router)
$url = $_GET['url'] ?? 'home';
require "controllers/$url.php";

// controller
$data = ["name" => "Aditya"];
require "views/home.php";

// view
echo $data['name'];

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🎯 High-Level Scoring Tips

✔ Use strict types
✔ Always use prepared statements
✔ Handle all errors properly
✔ Write modular code (MVC)
✔ Think like a backend developer