Thanks to Kathi Fisler, professor at WPI, for the assignment this is based on.

The Goals

• Use structs to model complex information
• Practice writing data definitions
• Practice using the design recipe for structs

The Assignment

A cellular phone company defines different service plans around three pieces of information: the region in which the plan is active, the number of minutes included, and whether the plan includes text messaging. The company defines three regions: Puget Sound, Pacific Northwest, and Nationwide.

1. Develop a data model for service plans. Include the define-struct needed to model plans and three examples of plans created with your model.
2. Develop a data model for customer subscriptions for cellular service. A subscription contains the customer’s name, number, service plan, and a discount code (one of none, long-dist-cust, or long-term-cust). Include the define-struct needed to model your subscriptions and three examples of data created with your model. You may choose/design your own data model for phone numbers (but be sure to document it if it’s not a built-in kind of data!).
3. Write a program regional-rate which consumes a region and returns the monthly rate for that region. Regional rates are according to the following table:
   

   Puget Sound	$19.95
   Pacific Northwest	$29.95
   Nationwide	$49.95

4. Write a program minutes-surcharge which consumes a number of minutes (assume non-negative) and returns the rate for that number of minutes. The first 150 minutes are free. Each 250 minutes beyond the first 150 costs $12. Your program should return only whole-number multiples of 12. For example, 151 minutes costs $12, 400 minutes costs $12, and 500 minutes costs $24.
5. Write a program message-surcharge which consumes a discount code and returns a number representing the rate for text messaging under that code. The rates should follow the table below:
   

   long-dist-cust	$3.95
   long-term-cust	$0 (free)
   none	$5.95

6. Write a program subscription-rate which takes a subscription and returns the total rate for that subscription. The subscription rate is the total of the regional rate, minutes surcharge, and messaging surcharge. The messaging surcharge should be 0 if the plan does not include messaging.
7. Write a program enable-messaging, which consumes a subscription and returns a subscription with the same name, number, and discount code as the original subscription, but with a plan that includes text messaging.

(4 votes, average: 2.50 out of 5)

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