How can PHP developers optimize their code to avoid errors related to unexpected characters in input, as seen in the forum thread?

PHP developers can optimize their code to avoid errors related to unexpected characters in input by sanitizing user input using functions like `htmlspecialchars()` or `mysqli_real_escape_string()`. These functions help prevent unexpected characters from causing issues such as SQL injection or cross-site scripting vulnerabilities.

// Sanitize user input using htmlspecialchars()
$user_input = htmlspecialchars($_POST['user_input']);

// Or using mysqli_real_escape_string()
$user_input = mysqli_real_escape_string($conn, $_POST['user_input']);