How to write a loop for repeat sales in c++?

The instructions are below

You have been asked to write a program to calculate sales totals for a general store. Your program will not know how many products each customer will buy, so your program will have to repeat the process until the last product has been entered (use -1 for Product ID to end each sale). After each sale your program must ask if you want to do another sale (1 continue, 0 end program). At the beginning of the day, the cash drawer has $500 in it. At the end of the program you must display how much money is in the drawer after handling all your sales transactions.

First part asks to write a loop for repeat sale.