What are some best practices for passing and using variables in PHP functions to ensure proper functionality?

When passing variables to PHP functions, it's essential to ensure proper data type consistency and avoid global variables to maintain code readability and reusability. One best practice is to explicitly pass variables as function parameters rather than relying on global scope, which can lead to unexpected behavior. Additionally, using type hints in function parameters can help enforce data type consistency and prevent errors.

// Passing variables as function parameters
function calculateTotal(int $quantity, float $price) {
    return $quantity * $price;
}

$quantity = 5;
$price = 10.99;

$total = calculateTotal($quantity, $price);
echo "Total: $" . $total;