Programming with
Microsoft Visual Basic 2010
5th Edition
CHAPTER SEVEN
SUB AND FUNCTION PROCEDURES
Previewing the Harvey
Industries Application
Open the Harvey Industries.exe file
The Harvey Industries application calculates payroll for an employee
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Programming with Microsoft Visual Basic 2010, 5th Edition
Previewing the Harvey
Industries Application (cont’d.)
Figure 7-1 Interface showing the payroll calculations
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Programming with Microsoft Visual Basic 2010, 5th Edition
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
Explain the difference between passing data by value and passing data
by reference
Create a Function procedure
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Programming with Microsoft Visual Basic 2010, 5th Edition
More About Sub Procedures
Procedure
◦ 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)
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Programming with Microsoft Visual Basic 2010, 5th Edition
Passing Variables
Variables
◦ Have both value and unique address
Passing by value
◦ Passes a copy of the variable’s value
◦ Example: Disclosing your bank account balance
Passing by reference
◦ Passes a variable’s address
◦ Example: Disclosing your bank account number
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Programming with Microsoft Visual Basic 2010, 5th Edition
Passing Variables by Value
Provides only contents of variable to receiving procedure
How to pass by value:
◦ Include keyword ByVal before parameter
Reasons to pass by value:
◦ Procedure needs to know contents of variable
◦ Procedure does not need to change original value
By default, Visual Basic passes by value
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Programming with Microsoft Visual Basic 2010, 5th Edition
Example: Event and Sub
Procedure
Programming with Microsoft Visual Basic 2010, 5th Edition
Figure 7-5 ShowMsg procedure and btnDisplay Click event procedure
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Programming with Microsoft Visual Basic 2010, 5th Edition
Passing Variables by Reference
Provides address (memory location) of variable to procedure
◦ Receiving procedure can thus access variable
Reason to pass by reference
◦ Procedure needs to change variable’s contents
How to pass by reference
◦ Include keyword ByRef before parameter
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Example (Using Sub
Procedures)
Programming with Microsoft Visual Basic 2010, 5th Edition
Figure 7-8 CalcGrossPay procedure and btnCalc control’s Click event procedure
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Programming with Microsoft Visual Basic 2010, 5th Edition
Function Procedures
Function procedure
◦ Block of code that performs specific task
◦ Returns 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
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Programming with Microsoft Visual Basic 2010, 5th Edition
Figure 7-14 Function procedure syntax, examples, and steps
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Programming with Microsoft Visual Basic 2010, 5th Edition
Function Procedures (cont’d.)
Figure 7-15 Examples of invoking the GetNewPrice function
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Programming with Microsoft Visual Basic 2010, 5th Edition
Example: Using Functions
Programming with Microsoft Visual Basic 2010, 5th Edition
Figure 7-16 CalcGrossPay function and btnCalc control’s Click event procedure
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Lesson A Summary
Two types of Sub procedures
◦ Event and independent
Function: Performs task and returns value
Independent procedures and functions
◦ Called from application’s code using Call statement
Pass by value
◦ Send copy of variable’s contents to procedure or function
Pass by reference
◦ Send variable’s address to procedure or function
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Programming with Microsoft Visual Basic 2010, 5th Edition
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
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Programming with Microsoft Visual Basic 2010, 5th Edition
Including a Combo Box in an
Interface
Combo box
◦ Allows user to select from number of choices
◦ Allows user to type 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
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Programming with Microsoft Visual Basic 2010, 5th Edition
Including a Combo Box in an
Interface (cont’d.)
Figure 7-19 Examples of the combo box styles
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Programming with Microsoft Visual Basic 2010, 5th Edition
Figure 7-20 Code associated with the combo boxes in Figure 7-19
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Programming with Microsoft Visual Basic 2010, 5th Edition
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 value that appears in text portion
Use label control to provide keyboard access to the combo box
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Programming with Microsoft Visual Basic 2010, 5th Edition
Including a Combo Box in an
Interface (cont’d.)
Figure 7-22 Gross pay amount shown in the interface
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Programming with Microsoft Visual Basic 2010, 5th Edition
Lesson B Summary
Use ComboBox tool to add combo box to 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
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Programming with Microsoft Visual Basic 2010, 5th Edition
Lesson B Summary (cont’d.)
Use SelectedIndex, SelectedItem, or Text property:
◦ To select combo box item from code
◦ To determine item that was selected
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Programming with Microsoft Visual Basic 2010, 5th Edition
Lesson C Objectives
After studying Lesson C, you should be able to:
Prevent a form from closing
Round a number
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Programming with Microsoft Visual Basic 2010, 5th Edition
Creating the Harvey Industries
Application
Application objective is to calculate:
◦
◦
◦
◦
Employee’s weekly gross pay
Federal withholding tax (FWT)
Social Security and Medicare (FICA) tax
Net pay
Review TOE chart for requirements
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Programming with Microsoft Visual Basic 2010, 5th Edition
Coding the Harvey Industries
Application (cont’d.)
Figure 7-26 User interface for the Harvey Industries application
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Programming with Microsoft Visual Basic 2010, 5th Edition
Coding the FormClosing Event
Procedure
FormClosing event
◦ Occurs when form is about to be closed because:
◦ Computer processes Me.Close() statement
◦ User clicks Close button on form’s title bar
Requirement for 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
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Programming with Microsoft Visual Basic 2010, 5th Edition
Coding the FormClosing Event
Procedure (cont’d.)
Figure 7-27 Pseudocode for the FormClosing event procedure
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Programming with Microsoft Visual Basic 2010, 5th Edition
Coding the FormClosing Event
Procedure (cont’d.)
Figure 7-28 Message box displayed by the code
in the FormClosing event procedure
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Programming with Microsoft Visual Basic 2010, 5th Edition
Coding the btnCalc Control’s
Click Event Procedure
Figure 7-29
Pseudocode for
the btnCalc
control’s Click
event procedure
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Programming with Microsoft Visual Basic 2010, 5th Edition
Coding the btnCalc Control’s
Click Event Procedure (cont’d.)
Figure 7-30 Selection structure entered in the procedure
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Programming with Microsoft Visual Basic 2010, 5th Edition
Creating the GetFwt Function
How to calculate weekly taxable wages
◦ Multiply number of withholding allowances by $70.19
◦ Subtract this result from weekly gross pay
Determining federal withholding tax (FWT)
◦ Evaluate weekly taxable wages and filing status
◦ Use data to look up FWT in special FWT tables
GetFwt function emulates FWT table lookup
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Programming with Microsoft Visual Basic 2010, 5th Edition
Creating the GetFwt Function
(cont’d.)
Figure 7-33 FWT calculations for a married taxpayer
whose weekly taxable wages are $388.46
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Programming with Microsoft Visual Basic 2010, 5th Edition
Creating the GetFwt Function
(cont’d.)
Figure 7-34 FWT calculations for a single taxpayer whose
weekly taxable wages are $600
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Creating the GetFwt Function
(cont’d.)
Figure 7-35 Pseudocode for the GetFwt function
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Programming with Microsoft Visual Basic 2010, 5th Edition
Creating the GetFwt Function
(cont’d.)
Figure 7-36 GetFwt function header and footer
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Programming with Microsoft Visual Basic 2010, 5th Edition
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
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Programming with Microsoft Visual Basic 2010, 5th Edition
Completing the btnCalc Control’s
Click Event Procedure (cont’d.)
Figure 7-37 Payroll calculations displayed in the interface
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Programming with Microsoft Visual Basic 2010, 5th Edition
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
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Programming with Microsoft Visual Basic 2010, 5th Edition