CS 230 Fall 2009                                                Assignment 7 – More Looping                                                       100 Assignment points

Assigned: 10/26/2009

Due: 11/03/2009 at the start of class

Pre-Lab (Do Before Lab):  Bring materials – a way to save a copy for you and a copy to turn in. Plan out tasks, objects, and events needed for program. Write pseudocode for the main button.

Main Assignment:

We’re going to implement a credit card simulation program. Write a program that shows month-by-month how long it takes to pay off a credit card balance when only paying the minimum payment each month.  Get from the user the amount borrowed and the annual  interest rate to be paid.  Display in a RichTextBox for each month elapsed, the number of months elapsed to that point, the interest owed that month, the minimum payment (see below), and the new balance (after interest has been charged and minimum payment paid).  

After the balance has been paid off, display in labels or read-only textboxes the total number of months needed to pay off the balance and the total amount paid over the course of that time.

NOTE – this task MUST be done with a loop – I need to see the month by month results in the rich text box – and in order to see that, you cannot do a single one-time calculation. 

· Provide capabilities to 1) simulate, 2) clear (the inputs and outputs) to start again, and 3) to exit.

Please set the name of the project to something other than the default name (WindowsApplication1, …). It is helpful if you use a name that identifies you as well as the assignment (e.g. yourlastname assignment 7).

Background Knowledge:

· The interest rate is annual, but in doing your monthly calculations, you don’t get a full year’s worth of interest in a month!  Assume months are equal length to keep this simple. i.e. if the annual interest rate is 0.12, then the interest rate for a month is 0.01. If any questions, please ask!!!  Your calculations need to meet the requirements of the task

· The minimum payment is determined as follows –

o In general, the minimum payment is enough to pay the current interest plus 1 percent of the current balance (e.g. with $1000 owed and .12 interest rate, interest is $10, and 1% of the balance is $10, so the minimum payment is $10 + $10 = $20)

o However, the lowest minimum payment allowed is $10, unless …

o The minimum payment never is higher than paying off the whole remaining balance.

· The order of calculations matters. In this case, the starting balance is the basis of calculating the first month’s interest. The minimum payment is determined after new interest is charged. The payment is made after interest is charged.  The resulting new balance becomes the starting point for determining the next month’s interest. And so on.

Task Details:

· HINT: Can you use a “for next” loop? (Do you know when you reach the top of the loop how many times it will need to go around?)

· The annual interest rate should be entered as a decimal instead of a percent (this makes your job a little easier).

• Define numbers (especially those that could change sometime in the futures) as named constants
• We’re no longer going to assume that the clerk enters valid and reasonable values.  Ensure that the amount borrowed and the interest rate are numeric, and that the amount borrowed is positive, and the interest rate is between .03 and .33.  Don’t try to calculate anything if bad data has been entered (display a message).
• Don’t worry about rounding to cents during calculations (but do display results formatted as currency)
• MAKE SURE YOUR PROGRAM WORKS! (i.e. gets the correct answers).  It doesn’t have to just run, it needs to run correctly!  It should run on any inputs (We are now branching and looping – so the program must be tested on more inputs to ensure that all paths through the program code work!). For instance, does your program still do the right thing no matter how many of the inputs are invalid?   Think up some different examples to test the program on.  For each, calculate the correct answer by hand or in Excel and see if your program gets it!

Miscellaneous

• You must turn on Option Explicit and Option Strict.
• Put YOUR NAME, e-mail address, date, and purpose of the program in comments at the beginning of the program. The purpose should be what the program is supposed to do, not the learning goals.  
• You MUST include comments that explain your program in order to get full credit.
• Any variables that you declare should have meaningful names – descriptive of the data that they hold.
• Remember to indent to show the structure of the program (VB usually does this correctly).
• Name all textboxes and buttons and the rich text box (and any labels referred to in code) meaningfully, and use conventions for ending their names.
• Make textboxes that user should never enter a value in (results / outputs) “Read Only” (or use labels). Make the rich text box “Read Only”.
• Put your name on the form as a Label or as part of the form title.
• Try to use good user interface design. Make clear what user needs to do and what the answers mean. Make error messages as clear and helpful as possible!
• This is related to “the essential question”. I’ll leave that as an exercise for the reader.

Hand in:

• Compressed (zipped) folder with your entire project containing all files related to the project, submitted to Blackboard.  Please name the zip file something along the lines of yournameAssignment7
• Print out of your code.