You can make use of dot notation to find the selected items without having to loop through the rows. This can also be used to get the number of selected rows by looking at the array size.

Long ll_count
Long ll_customer_id[]

// Get each of the selected
ll_customer_id = dw_customers.Object.customer_id.Current.Selected

// Find the number of selected items by finding the size of the array
ll_count = upperBound(ll_customer_id)