Design a vending machine. The vending machine should allow a user to:

• Select a product from a list of available products.
• Insert money into the vending machine.
• Receive the selected product if enough money has been inserted.
• Receive any change due after a successful purchase.
• Cancel the transaction and receive a refund of the inserted money.
• The vending machine should also allow an administrator to:
  • Add new products to the vending machine.
  • Restock existing products.
  • Withdraw money from the vending machine.
  • Set product prices.

Requirements