Programming with Microsoft Visual Basic 2010 5 th Edition

Programming with Microsoft Visual Basic 2010 5th Edition

CHAPTER SEVEN

SUB AND FUNCTION PROCEDURES

Programming with Microsoft Visual Basic 2010, 5th Edition

Previewing the Harvey Industries Application

Open the Harvey Industries.exe file

The Harvey Industries application calculates payroll for an employee

2


Previewing the Harvey Industries Application (cont’d.)

3

Figure 7-1 Interface showing the payroll calculations


Lesson A ObjectivesAfter 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

4


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)

5


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

6


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

7


Example: Event and Sub Procedure


Figure 7-5 ShowMsg procedure and btnDisplay Click event procedure9


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

10


Example (Using Sub Procedures)


Figure 7-8 CalcGrossPay procedure and btnCalc control’s Click event procedure

12


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

13

Programming with Microsoft Visual Basic 2010, 5th Edition14

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


Function Procedures (cont’d.)

15

Figure 7-15 Examples of invoking the GetNewPrice function


Example: Using Functions


Figure 7-16 CalcGrossPay function and btnCalc control’s Click event procedure


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

18


Lesson B ObjectivesAfter 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

19


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

20


Including a Combo Box in an Interface (cont’d.)

21

Figure 7-19 Examples of the combo box styles


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



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

23



24

Figure 7-22 Gross pay amount shown in the interface


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

25


Lesson B Summary (cont’d.)

Use SelectedIndex, SelectedItem, or Text property:◦ To select combo box item from code◦ To determine item that was selected

26


Lesson C ObjectivesAfter studying Lesson C, you should be able to:

Prevent a form from closing

Round a number

27


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

28


Figure 7-26 User interface for the Harvey Industries application

Coding the Harvey Industries Application (cont’d.)

29


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

30


Coding the FormClosing Event Procedure (cont’d.)

31

Figure 7-27 Pseudocode for the FormClosing event procedure


Coding the FormClosing Event Procedure (cont’d.)

32

Figure 7-28 Message box displayed by the code in the FormClosing event procedure


Coding the btnCalc Control’s Click Event Procedure

33

Figure 7-29 Pseudocode for

the btnCalc control’s Click

event procedure


Coding the btnCalc Control’s Click Event Procedure (cont’d.)

34

Figure 7-30 Selection structure entered in the procedure


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

35


Creating the GetFwt Function (cont’d.)

36

Figure 7-33 FWT calculations for a married taxpayer whose weekly taxable wages are $388.46



37

Figure 7-34 FWT calculations for a single taxpayer whose weekly taxable wages are $600



38

Figure 7-35 Pseudocode for the GetFwt function



39

Figure 7-36 GetFwt function header and footer


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

40


Completing the btnCalc Control’s Click Event Procedure (cont’d.)

41

Figure 7-37 Payroll calculations displayed in the interface


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

42

Programming with Microsoft Visual Basic 2010 5 th Edition

Documents

Transcript of Programming with Microsoft Visual Basic 2010 5 th Edition