The Top 8 PHP Interview Questions Every Hiring Manager Should Ask

1. The provided array will consist of consecutive integers with a single missing integer.
2. A minimum of two elements will be present in the array.

$count = count($numbers);

$total = (($count + 1) * ($count + 2)) / 2;

$sum = array_sum($numbers);

return $total – $sum;

}

print_r(findMissingNumber(array(1, 2, 4, 5, 6)));

1. Not taking into account that only one number is missing.
2. Using iterative methods, which may not be efficient for larger arrays.

How would you handle negative numbers?

1. The file will have at least one number.
2. The file can have empty lines or lines with characters that aren’t numbers.
3. Every number within the file will be an integer.

    $sum = 0; 

    try {

        $file = new SplFileObject($filePath);       

        while (!$file->eof()) {

            $line = $file->fgets();           

            if (is_numeric($line)) {

                $sum += (int)$line;

            }

        }

    } catch (Exception $e) {

        echo “An error occurred: “ . $e->getMessage();

    }

    return $sum;

}

echo readFileAndSumNumbers(“numbers.txt”);

1. Not handling exceptions properly, which can lead to system crashes if the file doesn’t exist or isn’t accessible.
2. Not checking for numeric values correctly, potentially causing non-numeric values to be added or throwing errors.

1. How would you modify the function to return the average of the numbers instead of the sum?
2. How can you ensure the file is properly closed after reading?

    return (filter_var($email, FILTER_VALIDATE_EMAIL)) ? true : false;

}

echo isValidEmail(‘john@example.com’) ? ‘Valid’ : ‘Invalid’;

1. Overcomplicating the solution by manually crafting a regular expression instead of leveraging built-in PHP functions.
2. Not accounting for edge cases in email validation, such as domain extensions or special characters.

1. How would you modify the function to validate that the email’s domain exists?
2. Are there any limitations to using filter_var() with FILTER_VALIDATE_EMAIL in certain scenarios?

1. Create a PHP class named Circle. This class should encompass a private property called radius.
2. Add a constructor for defining the radius.
3. Integrate two public methods: getArea and getCircumference.

These methods will be employed to compute the area and the circumference of the circle in that order.

    private $radius;

    public function __construct($radius) {

        $this->radius = $radius;

    }

    public function getArea() {

        return pi() * pow($this->radius, 2);

    }

    public function getCircumference() {

        return 2 * pi() * $this->radius;

    }

}

$circle = new Circle(5);

echo “Area: “ . $circle->getArea();

echo “\nCircumference: “ . $circle->getCircumference();

1. Not using proper encapsulation by making the radius property public instead of private.
2. Incorrect formulas for area or circumference.
3. Failing to utilize built-in PHP functions like pi() and pow() for mathematical computations.

1. Why is the radius property declared private, and why might that be important?
2. How could you extend this class to incorporate other shapes or functionalities, like resizing the circle?

    // Create connection

    $conn = new mysqli($hostname, $username, $password, $dbname);  

    // Check connection

    if ($conn->connect_error) {

        die(“Connection failed: “ . $conn->connect_error);

    }

    $sql = “SELECT * FROM users”;

    $result = $conn->query($sql);

    $users = [];

    while($row = $result->fetch_assoc()) {

        $users[] = $row;

    }

   $conn->close();

    return $users;

}

1. Not handling database connection errors, which could lead to undescriptive failure messages or application crashes.
2. Forgetting to close the database connection after operations are completed.
3.  Not validating or sanitizing inputs, potentially leading to SQL injection vulnerabilities.

1. How would you modify this function to handle other types of databases, such as PostgreSQL?
2. How would you incorporate prepared statements to enhance security against SQL injection?
3. Discuss how you’d handle more complex queries or join operations to fetch data from multiple tables.

    // Hold the class instance.

    private static $instance = null;

    // The constructor is private to prevent initiation with outer code.

    private function __construct() {}

    // The object is created from within the class itself only if the class has no instance.

    public static function getInstance() {

        if (self::$instance == null) {

            self::$instance = new Singleton();

        }

        return self::$instance;

    }

}

The provided solution follows this pattern:

• Making the constructor private so the class cannot be instantiated from outside.
• Utilizing a private static property $instance to hold the single instance of the class.
• Introducing a public static method getInstance() that either returns the existing instance or creates a new one if none exists.

1. Not making the constructor private, allowing external code to create multiple instances.
2. Forgetting to check for existing instances before creating a new one, leading to potential multiple instances.
3. Not making the $instance property static would make it tied to an instance rather than the class.

1. Why is the Singleton pattern sometimes criticized? What are its potential downsides in software design?
2. How does the Singleton pattern differ from other creational design patterns?
3. Discuss scenarios where the Singleton pattern would be an appropriate choice and where it might not be suitable.

    $startMemory = memory_get_usage();

    sort($largeArray);

    $endMemory = memory_get_usage();

    $memoryUsed = $endMemory – $startMemory;

    return $memoryUsed;

}

1. Determines the current memory usage before performing any operations using memory_get_usage().
2. Sorts the input array using PHP’s built-in sort() function.
3. Determines the memory usage after the sorting operation.
4. Calculates the difference between the initial and final memory usage, which gives the amount of memory used during the operation.
5. Returns the calculated memory difference.

1. Not recording memory usage both before and after the operation would lead to incorrect calculations.
2. Modifying the original array in ways other than what’s described in the task causes memory measurements to be off.
3. Using functions other than memory_get_usage() may not give accurate or relevant results.

1. In what scenarios might PHP’s memory usage be a concern, and how can you mitigate excessive memory consumption?
2. How does PHP’s garbage collector work, and how does it help in managing memory?
3. What are other methods or tools you can use to monitor and optimize memory usage in PHP applications?

session_start();

// Set session variable

$_SESSION[“favorite_color”] = “blue”;

// Get session variable

$favoriteColor = $_SESSION[“favorite_color”];

1. Initiating a new session using the session_start() function.
2. Setting a session variable named “favorite_color” with a value of “blue“.
3. Retrieving and storing the value of the session variable “favorite_color” in the $favoriteColor variable.

• Forgetting to start the session using session_start() before using the $_SESSION superglobal.
• Incorrectly spelling or referencing session variable names, leading to undefined index errors.
• Not understanding the life cycle of a session or how data persists across different requests.

1. How can you destroy a session in PHP, and why might you want to do so?
2. What precautions should you take when storing sensitive data in session variables?
3. Describe other mechanisms in PHP for managing state across web requests. How do cookies differ from sessions in PHP?