What are some common causes of black question marks representing spaces in PHP code?

When black question marks appear in PHP code, it usually indicates that there is a character encoding issue, often caused by using a different character encoding than what is expected by the PHP interpreter. To solve this issue, make sure that your PHP files are saved with the correct character encoding, such as UTF-8.

// Make sure to save your PHP files with UTF-8 encoding
// Example: Save your file with UTF-8 encoding in a text editor like Notepad++

<?php
// Your PHP code here
?>