Preparing for Assignment 3

Setup

• Assignment 3 builds on Assignment 2, and we are using the same basic scenario. Save the spreadsheet you used for Assignment 2 as YourNameAssignment3, making sure it’s a macro-enabled workbook

• You will again have a model Ice Cream Order to follow along with, building on the first version used for Assignment 2

Before Writing the Code:Requirements

• Remember, writing is the third step of the process, not the first!

• Start by reviewing the requirements and making up some use cases and tests. You will need at least five or six tests to do a good job

• Think about the process. What should happen first? What next? Work through a typical use case on paper

Before Writing the Code:Specification

• Start by making a plan. If you don’t want to do a flowchart for the whole program, write down the major steps in English (this is called “pseudo code”)

• Think about what variables and constants you might need

• We used our pseudo code steps as major comments in our code; you can write these first and then fill in

• You will need to hand in a flow chart for the conditionals that control what happens with the option buttons

Writing the Code

• It is a HUGE mistake to write all the code and then try to debug it

• Write a small piece and run it to make sure it works. Then write another small piece

• This way if there is a bug you know it is probably in the small piece of new code you just wrote. You don’t have to hunt for it through the new program

• If you get a runtime error, click on debug and VBA will highlight the line where the error occurred. You can also step through your code.

Give Yourself Enough Time

• Things may go well but when writing code it is common to get a hard-to-find bug or two

• Start early so you have plenty of time to hunt them down

• Use the TA and the message boards, but please don’t post large chunks of code on the boards; you can mail code to the TA if you want him or her to look at it

A FEW NEW TOOLS…

The UserForm_Initialize Event

• UserForm_Initialize is similar to Workbook_Open; it’s an event routine that is called when the form is loaded into memory

• We used named constants to define the various prices for options; the labels for the buttons and check boxes are completed using these at load time

• This allows us to provide the information in one place only, so it is easy to change if we need to

Formatting

• We used formatting functions to make our numbers print nicely

• Format(TIPPERCENT, "Percent") formats the number TIPPERCENT, which is a constant equal to .15, as 15%

• We also used the “Currency” format. Note: if you bought your computer in another country, it may format in a currency other than dollars. This is OK; you don’t have to change it.

Error Handling

• In a well-written program, user mistakes are caught and the user is given a chance to correct them

• Often this type of code is a large, even major, part of the program

• We haven’t done much in this regard yet but we did catch the mistake if no commission option is selected

Note error handling in the Else clause

If optVanilla.Value = True Then flavorName = "vanilla" flavorPrice = VANILLAPRICE ElseIf optChocolate.Value = True Then flavorName = "chocolate" flavorPrice = CHOCOLATEPRICE ElseIf optStrawberry.Value = True Then flavorName = "strawberry" flavorPrice = STRAWBERRYPRICE Else 'no option chosen MsgBox ("You need to select a flavor") Exit Sub End If