How can visibility of variables impact the functionality of PHP functions within a script?

The visibility of variables within a PHP function can impact its functionality if variables are not properly scoped. To ensure that variables are accessible within a function, they should either be passed as parameters or declared as global variables within the function.

// Using parameters to pass variables to a function
function calculateSum($num1, $num2) {
    return $num1 + $num2;
}

$result = calculateSum(5, 3);
echo $result; // Output: 8

// Using global variables within a function
$num1 = 5;
$num2 = 3;

function calculateSum() {
    global $num1, $num2;
    return $num1 + $num2;
}

$result = calculateSum();
echo $result; // Output: 8