What potential issues can arise when using global variables in PHP scripts?

Using global variables in PHP scripts can lead to potential issues such as variable scope conflicts, difficulty in tracking variable changes, and security vulnerabilities. To mitigate these problems, it's recommended to limit the use of global variables and instead use function parameters or return values to pass data between functions.

// Avoid using global variables and pass data through function parameters or return values instead

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

$number1 = 5;
$number2 = 10;

$result = calculateSum($number1, $number2);

echo "The sum of $number1 and $number2 is: $result";