Assignment Number 4 SE4D04 Page 1 of 7 The Design of the Computer-User Interface

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1 Assignment Number 4 SE4D04 Page 1 of 7 "Mortgage Payment Calculator" DESIGN - A program, which can be downloaded in source form with this assignment) has been created in a VB8 form (Windows.net V2), that replicates the illustration (Figure 1) at the right, upon first execution. Briefly, the user inputs the amount of money borrowed and the applicable interest rate in separate text boxes, suitably labeled for this purpose, as well as the payment schedule (once or twice monthly), and the duration of the loan, whereupon the calculator will output the payment($) required per the pay period. COMPONENTS (As given in Figure 2.) - 'include Text Boxes, Command Buttons, Option (Radio) Buttons, Check Buttons, and uses built-in Financial functions. (See last page of assignment.) A single form (default colour and shape) which is sized to about 75% of the total vertical available screen space and its title bar contains Assignment #, student name and Id ; Two Command Buttons captioned as follows: 1. Calculate 2. Close Four TextBoxes: 1. User input for an integer amount of Figure 1: The first screen that appears upon program execution. All buttons and user input boxes are active. dollars representing the amount borrowed (loan amount) labeled as Amount Borrowed ; 2. User input box for an integer representing the expected interest rate (in percentage); 3. Two text output boxes used by the program to provide the Payment($) per pay period (selected via checkboxes (see below)) either monthly or twice monthly, and the total amount of interest paid for the duration of the loan period; One set (i.e. a panel as a container) of intrinsic (only one can be user set) radio buttons which exhibit automatically mutually exclusive selection (i.e. only one button can be selected, removing another set button if one is already selected) representing the amortization period in integer years for explicit values of 15, 20, 25 & 30 years; and One set of checkboxes that must be manually programmed to behave mutually exclusively upon selection (as do the radio buttons where only one can be set), involving either twice monthly payment bi-monthly or once monthly monthly payments.

2 Assignment Number 4 SE4D04 Page 2 of 7 FUNCTIONALITY - Events: 1. On form load (or program execution run from *.exe file when compiled) all components display as shown in Figure 1. If the user selects Close, the program performs a normal stop and returns to the operating system. 2. If the user selects Calculate, (if inputs are properly assignment values (see below)) the program calculates, by using the built-in financial functions Pmt and Ipmt. The amount payable each period and The total interest payable over the lifetime of the mortage. 3. Upon output of the Payment/Period and Figure 2: This is the appearance of VB8 solution to the Total Interest($) assignment at design time, showing the two command buttons, the four textboxes, the four radio buttons and values in the textboxes two checkboxes, and their accompanying labels. (sutitably formatted as currency before displaying in the relevant textboxes), the program determines which payment schedule has been selected and changes the label on the Payment($)/Period to either Payment($)/2xMnthly or Payment($)/Mnthly. This behaviour is illustrated in Figure 3.

3 Assignment Number 4 SE4D04 Page 3 of 7 Error Conditions: 1. The program must check that the input to these text boxes is numeric, if not, an error is displayed in a message box. A group of Option (Radio) Buttons allows selection of amortization period as 15, 20, 25,30 years. Use a default value of 20 years. Mortgage payment is made either monthly or twice a month '(Not bi-weekly) at the beginning of the period. This is selected by a pair of Check Buttons. Selection of one of these buttons must deselect the other (which needs to be explicitly implemented in the code). If both check buttons are unchecked, a message box displays error, as shown in Figure The program should also detect when the two input text boxes (labelled Amount Borrowed($) or Annual Rate of Interest(%) ) contain either nothing (are null), or contain non-numeric characters, which is illustrated in Figure NOTE: it is possible upon first screen execution to not have one radio button selected. This is an unhandled exception which should be handled in any manner you feel is appropriate. (a (b Figure 3: (a) If the inputs are acceptable (i.e. they are not empty, contain integers, etc (see text) to the program, when the Calculate button is pressed, (b) both Payment($)/Period and Total Interest ($) are calculated and placed into the appropriate textbox. Also, the Payment($)/Period is changed to either Payment($)/2xMnthly or Payment($)/Mnthly, depending on which Payment Schedule is selected by the user: Bimonthly or Monthly, respectively.

4 Assignment Number 4 SE4D04 Page 4 of 7 (a) (b) (c) (d) Figure 4: (a) If the Calculate button is clicked and NO Payment Schedule is selected, then a program pops up a modal window which must be acknowledged by the user (OK pressed), (b) when this is done, the program rewrites the Payment($) / Mnthly (or whatever) label back to Payment($) / Period ; (c) If the Calculate button is clicked and TWO Payment Schedules are selected, then a program pops up a modal window which must be acknowledged by the user (OK pressed), (d) When user inputs a Payment Schedule via checkbox & presses calculate, the behaviour is as in step 3 above, under Events heading.

5 Assignment Number 4 SE4D04 Page 5 of 7 (b) (a) Figure 5: (a) If either or both of the two input textboxes (Amount Borrowed($) or (Annual Rate of Interest(%)) contain null or non-numeric characters), the program will popup a modal error window, as illustrated (a) and (b); while, in (c) the null Payment Schedule brings out the usual error notification window as mentioned before, AFTER the detection and popup indicating non-numerical or null entries in either or both of the Amount Borrowed($) or Annual Rate of Interest(%) labeled textboxes, as put in by the user, and its subsequent dismissal (i.e. user selects OK in the popup as in either (a) or (b)). (c) In MS visual studio, the amortization payment schedule algorithm is an intrinsic (internal) function as outlined below.

6 Assignment Number 4 SE4D04 Page 6 of 7 PMT function Format PMT(principal;interestRate;term) Parameters principal - principal amount. interestrate - interest rate. If the interest rate is annual, divide the rate by 12. term - length of time, expressed in number of months. Data type returned number Description Returns the payment required to meet the requirements of the term, interestrate, and principal you supply. Examples In the following example, the PMT function calculates payments for purchasing a sports car costing $21,000, at an annual rate of 6.9% over 48 monthly payments. PMT(21000;.069/12;48) returns the payment amount $ PMT(Cost;.13;Years) returns a payment amount, based on the purchase value stored in Cost, at a 13 percent rate, over the duration stored in Years. "Your payment will be " & PMT(150000;.13/12;Months) & "." returns Your payment will be, followed by the payment amount, based on a total cost of $150,000, at a 13 percent annual percentage rate, over the duration stored in Months.

7 Assignment Number 4 SE4D04 Page 7 of 7 As a software engineer, interested in producing the best possible user interface, make ANY adjustments to this specific user interface that you feel could be done to improve usability for the end-user (e.g. use of colours, rearrangement of components (or even use of different components, if desired), presence or absence of components, different notices and behaviour on error conditions both from the point of view of notifying the user of a problem and how it can be more easily rectified). As a guide, I would expect 25% of the marks be allocated to the changes and another 25% derived from your reasoning given in the printed (word processed) report. Now do not go nuts and change everything! What is expected is for you to make changes to about half the things that are illustrated on the given solution and explain why you think that your changes improve something. WARNING, do not change the functionality of the program this is to be preserved at all costs. (You can add minor functionality, but the minimal set of operations, must still be present in your version, and you may even find that some of the calculations must be hand-coded if library intrinsic functions are not available in the programming environment you are working within. NOTE: the reason for this statement is that the fifth assignment is to reproduce your Mortgage Calculator in the WWW environment, using JavaScript and VBScript. In that assignment, you will be asked what the constraints are encountered by the designer as a result of selecting various programming environments: VB8 (this work), VBScript and JavaScript.) Severe mark reduction will occur if this functionality is compromised! HCI enhancements should always be checked for unintended adverse effects on program functionality. Good luck and may the force be with you! By the way, the force is like duct tape: it has a light side, it has a dark side, and it binds the universe together! END of the ASSIGNMENT