A vending machine sells 12 different soft drinks. Each drink costs €1.10. The price of the drink is clearly displayed or "Out of stock" is displayed where a particular drink is not available.
When a user wants to buy a drink, they insert their money (coins only) into the vending machine and select the drink. When the correct amount, or more than the correct amount, has been inserted, the drink that they selected is dispensed and change (if any) is given. If change is not available, the user is told "Change not available" and they can choose to still select the drink and forfeit the change, or they can cancel the order. If the correct change is available, the change is dispensed in the lowest number of coins possible (based on the coins in the machine).
The vending machine manager regularly goes to the machine to add more drinks and to remove any coins from the machine. He/She must have a key'. The manager can then add drinks to the machine (up to a maximum of 20 units per drink) and can remove money, but must leave coins available for change in the machine. The manager can also add coins if necessary to the machine. The boxes inside the machine store a maximum of 500 €2 coins, a maximum of 300 €1 coins and a maximum of 200 50c, 20c, 10c, 2c and lc coins. The manager can also have a report printed that indicates:
• The number of each drink sold.
• The amount of revenue generated. This should include the amount generated through sales and the amount generated through left change.
• The amount of money that was removed from the machine.