Instructions

A friend of yours has an old wholesale store called Gross Store. The name comes from the quantity of the item that the store sell: it's all in gross unit. Your friend asked you to implement a point of sale (POS) system for his store. First, you want to build a prototype for it. In your prototype, your system will only record the quantity. Your friend gave you a list of measurements to help you:

1. Store the unit of measurement in your program

In order to use the measurement, you need to store the measurement in your program.

2. Create a new customer bill

You need to implement a function that create a new (empty) bill for the customer.

3. Add an item to the customer bill

To implement this, you'll need to:

• Return false if the given unit is not in the units map.
• Otherwise add the item to the customer bill, indexed by the item name, then return true.
• If the item is already present in the bill, increase its quantity by the amount that belongs to the provided unit.

Note that the returned value is type bool.

4. Remove an item from the customer bill

To implement this, you'll need to:

• Return false if the given item is not in the bill
• Return false if the given unit is not in the units map.
• Return false if the new quantity would be less than 0.
• If the new quantity is 0, completely remove the item from the bill then return true.
• Otherwise, reduce the quantity of the item and return true.

Note that the returned value is type bool.

5. Return the quantity of a specific item that is in the customer bill

To implement this, you'll need to:

• Return 0 and false if the item is not in the bill.
• Otherwise, return the quantity of the item in the bill and true.

Note that the returned value are types int and bool.