Chapter 7: Sub and Function Procedures

Programming with Microsoft Visual Basic 2012

Chapter 7: Sub and Function Procedures

Previewing the Cerruti Company Application

Programming with Microsoft Visual Basic 2012 2

Figure 7-1 Interface showing the payroll calculations

Previewing the Cerruti Company Application (cont.)


Figure 7-2 Message box containing a confirmation message

Lesson A Objectives

After studying Lesson A, you should be able to:• Create and call an independent Sub procedure• 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


• Procedure– A block of program code that performs a specific task

• Two types of Sub procedures in Visual Basic:– Event procedure

• A procedure associated with a specific object and event– Independent Sub procedure

• Independent of any object and event• Processed only when called (invoked) by a Call statement


Sub Procedures


Sub Procedures (cont.)

Figure 7-3 Syntax and examples of an independent Sub procedure and the Call statement

• 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


Passing Variables

Figure 7-4 Illustrations of passing by value and passing by reference


Passing Variables (cont.)

Passing Variables by Value• Provides only the contents of the variable to the

receiving procedure• How to pass by value:

– Include the keyword ByVal before the parameter • Reasons to pass by value:

– The procedure needs to know the contents of the variable

– The procedure does not need to change the original value• By default, Visual Basic passes by value



Figure 7-5 Favorite Title application’s interface

Figure 7-6 Partially-coded btnDisplay_Click event procedure

Passing Variables by Value (cont.)



Figure 7-8 Message shown in the interface

Figure 7-7 DisplayMsg procedure




Figure 7-9 DisplayMsg procedure header and Call statement




Passing Variables by Reference• Provides the address (memory location) of the

variable to the procedure– The receiving procedure can thus access the variable

• Reason to pass by reference:– The procedure needs to change the variable’s contents

• How to pass by reference:– Include the keyword ByRef before the parameter



Figure 7-11 btnCalc_Click procedure from Chapter 6

Figure 7-10 Gross Pay application’s interface

Passing Variables by Reference (cont.)



Figure 7-12 Call statement entered in the procedure

Figure 7-14 Gross pay shown in the interface

Figure 7-13 CalcGross procedure




Figure 7-15 CalcGross and btnCalc_Click procedures




Figure 7-16 Desk-check table before the Call statement is processed

Figure 7-17 Desk-check table after the Call statement and CalcGross procedure header are processed




Figure 7-18 Desk-check table after the statement in the CalcGross procedure is processed


• Function procedure– A block of code that performs a specific task– Returns a value after completing its task– Visual Basic provides built-in functions– You can also create your own functions

• As dataType in header indicates the return type of data– The Return statement is typically the last statement in a

function• The Return expression type must agree with the As dataType


Function Procedures


Function Procedures (cont.)

Figure 7-22 Syntax and examples of functions



Figure 7-23 Examples of invoking the GetNewPrice function



Figure 7-24 CalcGross function and btnCalc_Click procedure

Lesson A Summary

• There are two types of Sub procedures:– Event – Independent

• A function performs a task and returns a value• Independent procedures and functions are called from

an application’s code using the Call statement• Passing by value sends a copy of the variable’s contents

to a procedure or function • Passing by reference sends a variable’s address to a

procedure or function


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 number of items in the list portion of a

combo box• Sort the items in the list portion of a combo box• Determine the item either selected or entered in a

combo box• Code a combo box’s TextChanged event procedure



Including a Combo Box in an Interface

• Combo box– Allows the user to select from a number of choices– Allows the user to type an entry not on the list– Can save space on a form

• A list box only allows the user to select from a number of choices

• DropDownStyle property– Three values:

• Simple• DropDown (default)• DropDownList


Including a Combo Box in an Interface (cont.)

Figure 7-27 Examples of the combo box styles



Figure 7-28 Code associated with the combo boxes in Figure 7-27



Figure 7-29 Correct TabIndex values Figure 7-30 Gross pay amount shown in the interface



Figure 7-31 Modified code for the Gross Pay application


Lesson B Summary

• To add a combo box to a form:– Use the ComboBox tool in the toolbox

• To specify the style of a combo box:– Set the combo box’s DropDownStyle property

• To add items to a combo box:– Use the Items collection’s Add method– The method’s syntax is object.Items.Add(item)– In the syntax, object is the name of the combo box, and

item is the text you want added to the list portion of the control


Lesson B Summary (cont.)

• To automatically sort the items in the list portion of a combo box:– Set the combo box’s Sorted property to True

• To determine the number of items in the list portion of a combo box:– Use the Items collection’s Count property– Its syntax is object.Items.Count, in which object is the

name of the combo box• To select a combo box item from code:

– Use any of the following properties: SelectedIndex, SelectedItem, or Text


Lesson B Summary (cont.)

• To determine the item either selected in the list portion of a combo box or entered in the text portion:– Use the combo box’s Text property– However, if the combo box is a DropDownList style, you

also can use the SelectedIndex or SelectedItem property• To process code when the value in a combo box’s Text

property changes:– Enter the code in the combo box’s TextChanged event

procedure

Lesson C Objectives

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


Creating the Cerruti Company Application


Figure 7-33 TOE chart for the Cerruti Company application

Creating the Cerruti Company Application (cont.)


Figure 7-34 User interface for the Cerruti Company application

Coding the FormClosing Event Procedure

• FormClosing event– Occurs when a form is about to be closed because:

• The computer processes the Me.Close() statement • The user clicks the Close button on the form’s title bar

• Requirements for the FormClosing event procedure:– Verifying that the user wants to close the

application– Taking appropriate action based on the user’s

response• To prevent closing, set the Cancel property of the

FormClosing procedure’s e parameter to TrueProgramming with Microsoft Visual Basic 2012 35

Coding the FormClosing Event Procedure (cont.)


Figure 7-36 Message box displayed by the code in the FormClosing event procedure

Figure 7-35 Pseudocode for the FormClosing event procedure

Coding the btnCalc_Click Procedure


Figure 7-37 Pseudocode for the btnCalc_Click procedure

Coding the btnCalc_Click Procedure (cont.)


Figure 7-38 Listing of named constants and variables for the btnCalc_Click procedure



Figure 7-39 Selection structure entered in the procedure

Figure 7-40 Second selection structure entered in the procedure

Creating the GetFwt Function• To calculate weekly taxable wages:

– Multiply the number of withholding allowances by $73.08 (2012 withholding allowance value)

– Subtract this result from the weekly gross pay• To determine federal withholding tax (FWT):

– Evaluate the weekly taxable wages and filing status– Use data to look up the FWT in special FWT tables

• The GetFwt function emulates the FWT table lookup





Figure 7-41 Weekly FWT tables for the year 2012

Creating the GetFwt Function (cont.)



Figure 7-42 Example of a FWT calculation

Figure 7-43 Another example of a FWT calculation




Figure 7-44 Pseudocode for the GetFwt function

Figure 7-45 GetFwt function header and footer


Completing the btnCalc_Click Procedure


Rounding Numbers• You must call the GetFwt function from the btnCalc’s

Click event procedure• Math.Round function

– Rounds a value to a specific number of decimal places– Syntax: Math.Round (value[, digits])

• value is the numeric expression to work on• digits is the integer indicating the number of places to the

right of the decimal point

Completing the btnCalc_Click Procedure (cont.)


Figure 7-46 Syntax and examples of the Math.Round function

Rounding Numbers (cont.)



Figure 7-48 Payroll calculations using the first set of test data

Figure 7-47 Data for testing the Cerruti Company’s application (continues)



Programming with Microsoft Visual Basic 2012 47Figure 7-47 Data for testing the Cerruti Company’s application

Figure 7-49 Payroll calculations using the second set of test data

(continued)




Figure 7-50 Cerruti Company application’s code (continues)




(continued)




(continued)





Figure 7-50 Cerruti Company application’s code

(continued)




Lesson C Summary

• To process code when a form is about to be closed:– Enter the code in the form’s FormClosing event procedure– The FormClosing event occurs when the user clicks the

Close button on a form’s title bar or when the computer processes the Me.Close() statement

• To prevent a form from being closed:– Set the Cancel property of the FormClosing event

procedure’s e parameter to True, like this: e.Cancel = True


Lesson C Summary (cont.)

• To round a number to a specific number of decimal places:– Use the Math.Round function

• The function’s syntax is Math.Round(value[, digits]) – value is a numeric expression– digits (which is optional) is an integer indicating how

many places to the right of the decimal point are included in the rounding

• If the digits argument is omitted, the Math.Round function returns an integer

Chapter 7: Sub and Function Procedures

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