... modify code but you can modify other stuff like item name, item price, item quantity.
7.If you are doing billing and any product quantity becomes zero then in inventory status you will also get a warning of low quantity.
8.Whole application revolves around only one record file on the basis of which both billing and Inventory control unit depends and using of either billing or Inventory control options affects record.txt
9.Multiple real-life logic is also applied in the application.