In what ways can global variables lead to error-prone code and make debugging more challenging in PHP applications?

Global variables can lead to error-prone code and make debugging more challenging in PHP applications because they can be modified from anywhere in the code, making it harder to track changes and dependencies. To mitigate this issue, it is recommended to avoid using global variables whenever possible and instead pass variables as parameters to functions or use classes to encapsulate data.

// Avoid using global variables by passing variables as parameters to functions
function calculateTotal($price, $quantity) {
    return $price * $quantity;
}

$price = 10;
$quantity = 5;
$total = calculateTotal($price, $quantity);
echo "Total: $total";