What are the potential pitfalls of not defining variables within a function in PHP?

Not defining variables within a function in PHP can lead to potential issues such as variable scope conflicts, unexpected behavior, and difficulties in debugging code. To avoid these pitfalls, it is important to define all variables within a function to ensure clarity and prevent any unintended consequences.

function calculateTotal($price, $quantity) {
    $total = $price * $quantity;
    
    return $total;
}