Terminating a loop based on user input

How do I terminate a loop in a PL/SQL block depending upon user input.

For Example:
Suppose the purpose of the PL/SQL vlock is to display total of all the numbers entered by the user. The user enters one number after which a confirmation is asked whether he wants to enter more numbers. If the responds with a Y then the next number is asked. This continues till the user responds with N. Then the total of all the numbers are returned.