What potential issues can arise when using global variables in PHP functions, and what are some alternatives for passing necessary information?

Using global variables in PHP functions can lead to code that is harder to maintain and debug, as it becomes unclear where the variable is being modified. Instead of relying on global variables, it is recommended to pass necessary information as parameters to the function. This makes the code more modular and easier to understand.

// Using parameters to pass necessary information instead of global variables
function calculateTotal($quantity, $price) {
    return $quantity * $price;
}

// Example usage
$total = calculateTotal(5, 10);
echo $total; // Output: 50