Chapter 7: Sub and Function
Procedures
Programming with Microsoft Visual Basic
.NET, Second Edition
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
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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
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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
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Sub Procedures (continued)
• User-defined procedures
– You must call explicitly
– You can define parameters
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Including Parameters in a UserDefined Sub Procedure
Figure 7-2: Syntax for creating a user-defined Sub procedure
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Including Parameters in a UserDefined 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
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Including Parameters in a UserDefined 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
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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
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Passing Variables (continued)
Figure 7-3: Examples of passing variables by value
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Passing Variables (continued)
Figure 7-3: Examples of passing variables by value (continued)
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Passing Variables (continued)
Figure 7-4: Examples of passing variables by reference
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Passing Variables (continued)
Figure 7-4: Examples of passing variables by reference
(continued)
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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
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Function Procedures (continued)
Figure 7-6: User-defined function syntax and example
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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
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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
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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
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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
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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
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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
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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
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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
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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
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Coding the uiCalculateButton Click
Event Procedure
Figure 7-18: Pseudocode for the uiCalculateButton control’s
Click event procedure
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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
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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
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Coding the GetFwtTax Function
(continued)
Figure 7-23: Pseudocode for the GetFwtTax function
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Coding the GetFwtTax Function
(continued)
Figure 7-23: Pseudocode for the GetFwtTax function (continued)
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Completing the uiCalculateButton’s
Click Event Procedure
• You can call the GetFwtTax function from the
uiCalculateButton’s Click event procedure
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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
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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
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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
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Adding an Existing Form to a
Solution (continued)
Figure 7-30: Copyright form
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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
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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
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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
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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
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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
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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()
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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
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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
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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()
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