What are the differences between using urlencode() and http_build_query() in constructing URLs for PayPal transactions in PHP?

When constructing URLs for PayPal transactions in PHP, it is important to properly encode the data to ensure it is correctly formatted and secure. The urlencode() function is used to encode individual query string parameters, while http_build_query() is used to encode an array of parameters into a query string. Using http_build_query() is generally preferred as it can handle arrays and nested data structures more efficiently.

// Example of constructing a PayPal transaction URL using http_build_query()

$params = array(
    'amount' => 100.00,
    'currency' => 'USD',
    'description' => 'Payment for goods',
    'return_url' => 'https://example.com/success',
    'cancel_url' => 'https://example.com/cancel'
);

$queryString = http_build_query($params);
$paypalUrl = 'https://www.paypal.com/cgi-bin/webscr?' . $queryString;

echo $paypalUrl;