How can PHP developers ensure the safety and integrity of input values when working with user input?

PHP developers can ensure the safety and integrity of input values when working with user input by using functions like `htmlspecialchars()` to escape special characters and prevent XSS attacks, `mysqli_real_escape_string()` to prevent SQL injection attacks, and `filter_var()` to validate and sanitize input data. Additionally, developers should always validate and sanitize user input before processing or storing it in a database to prevent security vulnerabilities.

// Example of sanitizing user input using htmlspecialchars and mysqli_real_escape_string
$userInput = $_POST['input'];

// Sanitize input to prevent XSS attacks
$sanitizedInput = htmlspecialchars($userInput);

// Escape special characters to prevent SQL injection attacks
$escapedInput = mysqli_real_escape_string($connection, $sanitizedInput);