Its about the pay system of a shop.
The user enters a product ID,the interpreter gets the details from the file and appends it to a list and continues till the products are over.
If the user can't enter the ID he can add the product name directly which will get the details from the file and append to list again.
From the list the total price will be displayed and the product names which will be in the file.
There must also be a fucntion to delete a product from the list and make new sum accordingly.