1. Programming with Microsoft Visual Basic 2010 5th Edition
Chapter Seven
Sub and Function Procedures

2. Previewing Harvey Industries Application
Open the Harvey.exe file
The Harvey Industries application calculates payroll for an employee
Figure 7-1 Interface showing the payroll calculations

3. Lesson A Objectives After studying Lesson A, you should be able to:
Explain the difference between a Sub procedure and a Function procedure
Create a procedure that receives information passed to it
Create a Function procedure
Explain the difference between passing data by value and passing data by reference

4. More About Sub Procedures
A block of program code that performs specific task
Two types of Sub procedures in Visual Basic
Event procedure
Procedure associated with specific object and event
Independent Sub procedure
Independent of any object and event
Processed only when called (invoked)

5. Passing Variables Variables Passing by value Passing by reference
Have both value and unique address
Passing by value
Passes a copy of the variable’s value
Passing by reference
Passes a variable’s address

6. Passing Variables by Value
Provides only the contents of variable to receiving procedure (called procedure)
How to pass by value:
Include keyword ByVal before parameter
Reasons to pass by value:
Procedure needs to know the contents of variable
Procedure does not need to change original value
(此變數只會出現在assignment statement右邊)
By default, Visual Basic passes by value
example

7. Figure 7-5 ShowMsg procedure and btnDisplay Click event procedure
(定義程序時的參數)
(引用程序時的參數)
Figure 7-5 ShowMsg procedure and btnDisplay Click event procedure

8. Passing Variables by Reference
Provides the address of variable to receiving procedure
Address : memory location
Receiving procedure can thus change the value of the variable
Reason to pass by reference
Procedure needs to change variable’s contents
(此變數會出現在assignment statement左邊，異動值傳回呼叫的程式)
How to pass by reference
Include keyword ByRef before parameter
example

9. lstHours
lstRate
43.0
7.75
Figure 7-8 CalcGrossPay procedure and btnCalc control’s Click event procedure

10. Passing Variables by Reference (cont’d.)
Figure 7-9 Argument values before the Call CalcGrossPay statement is processed
program

11. alias (Called by ByRef) (Called by ByVal) program
Figure 7-10 Argument and parameter values after the Call statement and CalcGrossPay procedure header are processed
program

12. Figure 7-11 Argument and parameter values after the first statement in the CalcGrossPay procedure is processed
program

13. Figure 7-12 Argument and parameter values after the statement in the selection structure’s true path is processed
program

14. Figure 7-13 Argument and parameter values after the CalcGrossPay procedure ends
program

15. Function Procedures Function procedure
A block of code that performs specific task
Returns a value after completing its task
Visual Basic provides built-in functions
Can also create your own functions
As datatype in header indicates return type of data
Return expression type must agree with As datatype
Syntax & example

16. Figure 7-14 Function procedure syntax, examples, and steps

17. Invoking Function Procedures
Figure 7-15 Examples of invoking the GetNewPrice function

18. Sub procedure方式
Figure 7-16 CalcGrossPay function and btnCalc control’s Click event procedure

19. Lesson A Summary Two types of Sub procedures
Event and independent
Function: Performs task and returns a value
Independent procedures and functions
Called from application’s code using Call statement
Pass by value
Send a copy of variable’s contents to procedure or function
Pass by reference
Send variable’s address to procedure or function

20. Lesson B Objectives After studying Lesson B, you should be able to:
Include a combo box in an interface
Add items to a combo box
Select a combo box item from code
Determine the item either selected or entered in a combo box
Code a combo box’s TextChanged event procedure

21. Including a Combo Box in an Interface
Allows user to select from a number of choices
Allows user to type an entry not on list
Can save space on form
List box does not share features two and three
DropDownStyle property
Values: Simple, DropDown (default), DropDownList
comparison

22. Including a Combo Box in an Interface
cboCity
cboState
cboName
Figure 7-19 Examples of the combo box styles
Program for this UI

23. Figure 7-20 Code associated with the combo boxes in Figure 7-19

24. Including a Combo Box in an Interface (cont’d.)
To process code when Text property changes
Use TextChanged event procedure
Use Item collection’s Add method to add item
Other properties of combo box
Sorted: Sorts items in dictionary order
SelectedIndex: Used to select item in list portion
SelectedItem: Contains value of item selected
Text: Contains the value that appears in text portion
Use label control to provide keyboard access to the combo box
example

25. Including a Combo Box in an Interface (cont’d.)
Figure 7-22 Gross pay amount shown in the interface

26. Lesson B Summary Use ComboBox tool to add combo box to a form
Specify style of combo box using DropDownStyle property
Use Items collection’s Add method to add items to Combo box
Use combo box’s Sorted property to sort items in combo’s list
Enter code in combo box’s TextChanged event procedure
To process code when Text property changes
Usage of SelectedIndex, SelectedItem, or Text property:
To select combo box item from code
To determine item that was selected

27. Lesson C Objectives After studying Lesson C, you should be able to:
Prevent a form from closing
Round a number

28. Creating Harvey Industries Application
Application objective is to calculate:
Employee’s weekly gross and net pay (初步薪資與淨薪資)
Federal withholding tax (FWT)
Social Security and Medicare (FICA) tax
Net pay

29. Coding FormClosing Event Procedure
Occurs when form is about to be closed because:
Computer processes Me.Close() statement
User clicks Close button on form’s title bar
Typical functions of FormClosing event procedure
Verifying that user wants to close application
Taking appropriate action based on user’s response
To prevent closing
Set Cancel property of FormClosing procedure’s e parameter to true

30. Coding the FormClosing Event Procedure
Figure 7-27 Pseudocode for the FormClosing event procedure
result

31. Coding the FormClosing Event Procedure (cont’d.)
Figure 7-28 Message box displayed by the code in the FormClosing event procedure
 實作練習在429~430頁

32. Coding btnCalc Control’s Click EventUI
Figure 7-29 Pseudocode for the btnCalc control’s Click event procedure
 實作練習在431~432頁

33. Creating the GetFwt Function
GetFwt function emulates FWT table lookup
Determining federal withholding tax (FWT)
Evaluate weekly taxable wages (可稅週薪) and filing status
Use data to look up FWT in special FWT tables
How to calculate weekly taxable wages
Multiply number of withholding allowances by $70.19
Subtract this result from weekly gross pay
pseudocode

34. Creating the GetFwt Function (cont’d.)
Figure 7-35 Pseudocode for the GetFwt function

35. Creating the GetFwt Function (Married)
Figure 7-33 FWT calculations for a married (已婚的) taxpayer whose weekly taxable wages are $388.46

36. Creating the GetFwt Function (Single)
Figure 7-34 FWT calculations for a single (單身的) taxpayer whose weekly taxable wages are $600

37. GetFwt Function Header and Footer
Figure 7-36 GetFwt function header and footer
 實作練習在435~439頁

38. Completing the btnCalc Control’s Click Event Procedure
Must call GetFwt function from btnCalc’s Click event procedure
Math.Round function
Round value to specific number of decimal places
Syntax: Math.Round (value[, digits])
value: Numeric expression to work on
digits: Integer indicating number of places to right of decimal point
 實作練習在436~438頁

39. Adding an Existing Form to a Solution
Add an existing form to Chap07/Harvey Industries Solution
Make sure that added form uses a different form name from any form name of Harvey Industries Solution in
Visual Studio and disk file system
The splash screen for Country Charming Inn in Chapter 1 is to be integrated into Chap07/Harvey Industries Solution
The splash screen identifies the application’s author and copyright year, or shows welcome message
實作練習 : 需下載
Chap07/ Harvey Industries Solution
Chap07/Splash Solution
Chap02/Playtime Solution

40. Adding an Existing Form to a Solution
Figure 1-31: Completed splash screen 40

41. Adding an Existing Form to a Solution
Rename the form in Splash Solution
Project->加入現有項目->Find Splash Form.vb to add
Open a new form by Timer’s Tick event
Add following codes in the Tick event of the timer tmrExit
Me.Hide()
tmrExit.Enabled = False
Dim mForm As New frmMain
mForm.ShowDialog()
Me.Close()
Syntax used to instruct the computer to create an object from a class:
Dim variablename As New classname
Otherwise, the form frmMain will show up many times.
The name of the main form in Harvey Industries Solution 41

42. Include Image File for the Added Form
VB doesn’t import image files automatically for the added form.
You can do it by one of the following steps
Make the statement Me.picCountry.Image = …… as a comment
Click Splash Form’s PictureBox picCountry
Use the task box of the PictureBox to set up its image file (image file is in the Resources folder of the Chap07/Splash Solution ) 42

43. Assigning the Startup Form
When an application is started, VB.NET automatically invokes the form set as the Startup object of a project
The setup steps for Startup object are as follows:
Right click on the project in the Project Explorer Window to open the Properties Window
Click the Application tab in Properties Window
Click the Startup object ComboBox to set up the startup form → choose frmSplash 43

44. ShowDialog() vs. Show() Method
A form object’s ShowDialog() method allows you to display the form object on the screen with focus transfer (dialog-style interaction)
The syntax is: form.ShowDialog()
The form object’s Show() method allows you to display a form object on the screen without focus transfer
The syntax is: form.Show () 44

45. Show Another Form by a Button
Download Chap02/Playtime Solution, Chap07/Harvey Industries Solution
How to use a button to open a new form
Project->加入現有項目->Find Playtime Form.vb to add
Include Image File for the PictureBox PictureBox1
Add following codes in the Click event of a button Show Playtime on the Harvey Industries’ MainForm
Me.Hide() ‘Show a form at a time
Dim hForm As New frmPlaytime
hForm.ShowDialog()
Me.Show()
frmPlaytime.Show() or .ShowDialog() ‘Show 2 forms
frmPlaytime.Focus() (when using frmPlaytime.Show() )
The name of main form in Playtime Solution 45 45

46. Lesson C Summary
Use form’s FormClosing event procedure to process code when form is about to be closed
Set Cancel property of FormClosing event procedure’s e parameter to true to prevent form from being closed
Use Math.Round function to round number to specific number of decimal places