CS 230 Spring 2007                                          Assignment 6 – More Looping                                                         100 points

Assigned: 02/28/2007

Due: 03/14/2007 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 text box – and in order to see that, you cannot do a single one-time calculation. 

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

Hand in:

• Floppy disk  or CD-R with an entire folder containing all files related to the project. 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 6). Use Windows to copy the whole folder, instead of trying to “Save As”.
• Print out of your code.  

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).

· 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. If any questions, please ask!!!  Your calculations need to meet the requirements of the task.

· The minimum payment is determined as follows –

· 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 $20)

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

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

• 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).
• 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. Comments are indicated with a single quote (everything after the single quote is only for humans)
• You MUST include comments that explain your program in order to get full credit.
• Remember to use meaningful variable names
• 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 meaningfully, and use conventions for starting their names.
• Make textboxes (and rich text box) that user should never enter a value in (results / outputs) “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!