1. Chapter 7: Sub and Function Procedures
Programming with Microsoft Visual Basic .NET, Second Edition

2. Creating Sub and Function Procedures Lesson A Objectives
Explain the difference between a Sub procedure and a Function procedure
Create a procedure that receives information passed to it
Explain the difference between passing data by value and by reference
Create a Function procedure
Programming with Microsoft Visual Basic .NET, Second Edition

3. Procedures
A procedure is a block of program code that performs a specific task
Procedures in Visual Basic .NET can be either Sub procedures or Function procedures
Sub procedures do not return a value
Function procedures return a value after performing their assigned task
Programming with Microsoft Visual Basic .NET, Second Edition

4. Sub Procedures Event procedures
Called by Visual Basic .NET in response to an event
Every event procedure has at least two parameters
sender: the object that raised the event
e: information about the object
Programming with Microsoft Visual Basic .NET, Second Edition

5. Sub Procedures (continued)
User-defined procedures
You must call explicitly
You can define parameters
Programming with Microsoft Visual Basic .NET, Second Edition

6. Including Parameters in a User-Defined Sub Procedure
Figure 7-2: Syntax for creating a user-defined Sub procedure
Programming with Microsoft Visual Basic .NET, Second Edition

7. Including Parameters in a User-Defined Sub Procedure (continued)
User-defined Sub procedures have both a procedure header and procedure footer
You use the keyword Private to indicate that only the procedures in the current form can access the procedure
You use the keyword Public when you want to allow unlimited access to the procedure
The Sub keyword identifies the procedure as a Sub procedure
Programming with Microsoft Visual Basic .NET, Second Edition

8. Including Parameters in a User-Defined Sub Procedure (continued)
parameterlist
Lists the data type and name of memory locations used by the procedure to store the information passed to it
Specifies how each item of information is passed: either by value or by reference
The procedure footer for a Sub procedure is always End Sub
Programming with Microsoft Visual Basic .NET, Second Edition

9. Passing Variables Passing by value: makes a copy of the data
Use ByVal before the parameter name
This is the default if you do not specify
Passing by reference: passes the address of the data
Use ByRef before the parameter name
Programming with Microsoft Visual Basic .NET, Second Edition

10. Passing Variables (continued)
Figure 7-3: Examples of passing variables by value
Programming with Microsoft Visual Basic .NET, Second Edition

11. Passing Variables (continued)
Figure 7-3: Examples of passing variables by value (continued)
Programming with Microsoft Visual Basic .NET, Second Edition

12. Passing Variables (continued)
Figure 7-4: Examples of passing variables by reference
Programming with Microsoft Visual Basic .NET, Second Edition

13. Passing Variables (continued)
Figure 7-4: Examples of passing variables by reference (continued)
Programming with Microsoft Visual Basic .NET, Second Edition

14. Function Procedures Function procedure
A block of code that performs a specific task
Typically referred to as a function
You can create your own functions, referred to as user-defined functions
The Return statement alerts the computer that the function has completed its task and ends the function after returning the value of its expression
Programming with Microsoft Visual Basic .NET, Second Edition

15. Function Procedures (continued)
Figure 7-6: User-defined function syntax and example
Programming with Microsoft Visual Basic .NET, Second Edition

16. Using a List Box Control Lesson B Objectives
Add a list box to a form
Add items to a list box
Sort the contents of a list box
Select a list box item from code
Programming with Microsoft Visual Basic .NET, Second Edition

17. Using a List Box Control Lesson B Objectives (continued)
Determine the selected item in a list box
Round a number
Code a list box’s SelectedValueChanged event
Programming with Microsoft Visual Basic .NET, Second Edition

18. Completing the Payroll Application’s User Interface
The payroll application should allow Mr. Williams to enter an employee’s:
Name
Hours worked
Rate of pay
Marital status (either “Married” or “Single”)
Number of withholding allowances
Programming with Microsoft Visual Basic .NET, Second Edition

19. Completing the Payroll Application’s User Interface (continued)
The application should calculate the employee’s:
Weekly gross pay
Federal withholding tax (FWT)
Social Security and Medicare (FICA) tax
Net pay
Programming with Microsoft Visual Basic .NET, Second Edition

20. Adding a List Box to a Form
Use a list box control to display a list of choices from which the user can select zero choices, one choice, or more than one choice
The number of choices the user is allowed to select is controlled by the list box control’s SelectionMode property
The Windows standard for list boxes is to display a minimum of three selections and a maximum of eight selections at a time
Programming with Microsoft Visual Basic .NET, Second Edition

21. Adding Items to a List Box
The items in a list box belong to a collection called the Items collection
The first item in the Items collection appears as the first item in the list box
The second item in the Items collection appears as the second item in the list box, and so on
The first item has an index of zero
The second item has an index of one, and so on
Programming with Microsoft Visual Basic .NET, Second Edition

22. Adding Items to a List Box (continued)
Use the Items collection’s Add method to specify the items you want displayed in a list box control
When you use the Add method to add an item to a list box, the position of the item in the list depends on the value stored in the list box’s Sorted property
Programming with Microsoft Visual Basic .NET, Second Edition

23. The SelectedItem and SelectedIndex Properties
A list box’s SelectItem property and SelectedIndex property can be used both to:
Determine the item selected in the list box
Select a list box item from code
Programming with Microsoft Visual Basic .NET, Second Edition

24. The SelectedItem and SelectedIndex Properties (continued)
The selected item is also called the default list box item
Should be either the most used selection
Or, if all of the selections are used fairly equally, the first selection in the list
Programming with Microsoft Visual Basic .NET, Second Edition

25. Coding the uiCalculateButton Click Event Procedure
Figure 7-18: Pseudocode for the uiCalculateButton control’s Click event procedure
Programming with Microsoft Visual Basic .NET, Second Edition

26. Coding the GetFwtTax Function
The amount of federal withholding text (FWT) to deduct from an employee’s weekly gross pay is based on the employee’s:
Filing status: single (including head of household) or married
Weekly taxable wages
Programming with Microsoft Visual Basic .NET, Second Edition

27. Coding the GetFwtTax Function (continued)
To calculate the federal withholding tax you need to know the employee’s:
Gross pay amount
Marital status
Number of withholding allowances
Programming with Microsoft Visual Basic .NET, Second Edition

28. Coding the GetFwtTax Function (continued)
Figure 7-23: Pseudocode for the GetFwtTax function
Programming with Microsoft Visual Basic .NET, Second Edition

29. Coding the GetFwtTax Function (continued)
Figure 7-23: Pseudocode for the GetFwtTax function (continued)
Programming with Microsoft Visual Basic .NET, Second Edition

30. Completing the uiCalculateButton’s Click Event Procedure
You can call the GetFwtTax function from the uiCalculateButton’s Click event procedure
Programming with Microsoft Visual Basic .NET, Second Edition

31. Clearing the Contents of the Label Controls
The label controls should be cleared when the SelectedValueChanged event occurs for one of the list boxes in the interface
A list box’s SelectedValueChanged event occurs each time a different value is selected in the list box
Programming with Microsoft Visual Basic .NET, Second Edition

32. Completing the Payroll Application Lesson C Objectives
Add an existing form to a solution
Add a new module to a solution
Code the Sub Main procedure
Create an instance of a form
Display a form object using the ShowDialog method
Programming with Microsoft Visual Basic .NET, Second Edition

33. Adding an Existing Form to a Solution
The copyright screen for Interlocking Software Company is to be the splash screen for each custom application created by the company
The copyright screen identifies the application’s author and copyright year and includes the Interlocking Software Company logo
Programming with Microsoft Visual Basic .NET, Second Edition

34. Adding an Existing Form to a Solution (continued)
Figure 7-30: Copyright form
Programming with Microsoft Visual Basic .NET, Second Edition

35. Coding the Sub Main Procedure
Sub Main is a special procedure in Visual Basic .NET that can be declared as the “starting point” for an application
You can tell the computer to process the Sub Main procedure automatically when an application is started
Programming with Microsoft Visual Basic .NET, Second Edition

36. Coding the Sub Main Procedure (continued)
You enter the Sub Main procedure in a module
A module is a file that contains code that is not associated with any specific object in the interface
Programming with Microsoft Visual Basic .NET, Second Edition

37. Creating an Instance of a Form
A class definition (or class) specifies the attributes and behaviors of an object
When an application is started, Visual Basic .NET automatically processes the code contained in the Startup object
If the Sub Main procedure is the Startup object, neither the CopyrightForm class definition nor the PayrollForm class definition will be processed automatically
Programming with Microsoft Visual Basic .NET, Second Edition

38. Creating an Instance of a Form (continued)
To allow the payroll application to display the forms associated with the CopyrightForm and the PayrollForm classes, the Sub Main procedure will need to:
Instruct the computer to create the objects
Instruct the computer to display the objects on the screen
Programming with Microsoft Visual Basic .NET, Second Edition

39. Creating an Instance of a Form (continued)
Syntax used to instruct the computer to create an object from a class: Dim variablename As New classname
Programming with Microsoft Visual Basic .NET, Second Edition

40. Using a Form Object’s Show Dialog Method
The form object’s ShowDialog method allows you to display a form object on the screen
The syntax of the ShowDialog method is: form.ShowDialog()
Programming with Microsoft Visual Basic .NET, Second Edition

41. Summary
To pass a variable by value to a procedure, include the keyword ByVal before the parameter name in the procedure header’s parameterlist
To pass a variable by reference, include the keyword ByRef before the parameter name in the procedure header’s parameterlist
To add items to a list box, use the Items collection’s Add method
Programming with Microsoft Visual Basic .NET, Second Edition

42. Summary (continued)
To determine the item selected in a list box, or to select a list box item from code, set the list box’s SelectedItem property or its SelectedIndex property
To process code when a different value is selected in a list box, enter the code in either the list box’s SelectedValueChanged or SelectedIndexChanged event procedure
Programming with Microsoft Visual Basic .NET, Second Edition

43. Summary (continued)
To add an existing item to an application, click File on the menu bar then click Add Existing Item
To create an instance of an object from a class, use the syntax: Dim variablename As New classname
To display a form object on the screen, use the form object’s ShowDialog method, whose syntax is: form.ShowDialog()
Programming with Microsoft Visual Basic .NET, Second Edition