What common syntax errors should PHP developers be aware of when comparing usernames in a registration form?

PHP developers should be aware of common syntax errors when comparing usernames in a registration form, such as using a single equal sign (=) instead of a double equal sign (==) for comparison. This mistake can lead to unintended assignment rather than comparison. To avoid this error, developers should always use double equal signs when comparing values in PHP.

// Incorrect comparison using single equal sign
$username = "john_doe";

if($username = "john_doe") {
    echo "Username is correct";
}

// Correct comparison using double equal signs
$username = "john_doe";

if($username == "john_doe") {
    echo "Username is correct";
}