How can the PHP code be improved to prevent errors or unexpected behavior?

To prevent errors or unexpected behavior in PHP code, it is important to validate user input, sanitize data, handle exceptions, and use proper error handling techniques. Additionally, using strict data types, avoiding global variables, and following best practices such as using prepared statements for database queries can also help improve the code's reliability. 

// Example PHP code with improved error handling and data validation

// Validate user input
if(isset($_POST['username']) && !empty($_POST['username'])) {
    $username = $_POST['username'];
} else {
    die('Username is required');
}

// Sanitize data
$username = filter_var($username, FILTER_SANITIZE_STRING);

// Handle exceptions
try {
    // Code that may throw an exception
} catch(Exception $e) {
    echo 'An error occurred: ' . $e->getMessage();
}

// Proper error handling
mysqli_report(MYSQLI_REPORT_ERROR | MYSQLI_REPORT_STRICT);

// Strict data types
declare(strict_types=1);

// Avoid global variables
function getUserData() {
    $username = 'example';
    return $username;
}

// Use prepared statements for database queries
$stmt = $mysqli->prepare("SELECT * FROM users WHERE username = ?");
$stmt->bind_param("s", $username);
$stmt->execute();
$result = $stmt->get_result();

Keywords

error handling exception handling debugging code review unit testing

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