Decision Making

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Chapter 5

• Decision Making

2
Objectives

• Use the ComboBox control
• Use the IfThenElse structure
• Use a nested IfThenElse structure
• Use the Select Case structure
• Validate user input

3
Objectives

• Use the MessageBox class
• Use the string concatenation in code
• Use relational operators in code
• Use logical operators in code

4
Modifying the Automobile Loan Calculator
Application
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Opening the Project and Modifying the User
Interface

• Open the Automobile Loan Calculator program you
  created in Chapter 4
• Select the Form1 form in the main work area,
  right-click the form, and then click Lock
  Controls on the shortcut menu to unlock the form
• Increase the form height to 248 pixels

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Opening the Project and Modifying the User
Interface

• Select the Label3 control, along with
  txtnMonthlyPament, btnComputePayment, and
  btnReset controls
• Drag the controls down four marks on the
  positioning grid
• Add a Label and ComboBox control from the Toolbox
  window and position as shown on the next slide

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Label Control Properties
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ComboBox Control Properties
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ComboBox1 Control Properties
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Setting the Items Property

• Select the Items property in the Properties
  window
• Click the Collection build button
• Type the five items into the String Collection
  Editor, as shown on the following slide, and
  click the OK button
• Upon completion, lock the controls using the
  Format menu

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Modifying the Comment Header and Adding a Constant
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Resetting the ComboBox Value

• The SelectedIndex property of the ComboBox
  control is assigned the value of the items index
• When no item is selected, the SelectedIndex
  property is set to -1
• Add the following line of code to the end of the
  btnReset_Click Event Procedure

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Declaring Additional Variables

• Two additional variables are needed in the
  btnComputePayment_Click event procedure
• Scroll the code window until line 258 appears
• Enter line 259 as shown below

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Decision-Making Control Structures

• Decision making is the process of determining
  which of one or more paths to take
• IfThenElse structure
• Select Case structure

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IfThenElse Structure
Select Case Structure
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IfThenElse Structure for Auto Loan Calculator
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The MessageBox Class and the Show() Method

• The MessageBox class provides the ability to
  display a message to the user in a pop-up window
• The Show() method must be used to display a
  message with a title bar
• MessageBox.Show(Please enter the customers
  credit rating in the Credit rating list box.,No
  Credit Rating)

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The Focus() Method

• When a user selects a control on a form, the
  control is said to have focus
• It is often necessary to set the focus to a
  control during run time
• cmbCreditRating.Focus()

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IfThenElse Statement

• Relational expression
• , lt, gt, lt, gt, ltgt
• Single-line IfThenElse statement
• Block IfThenElse statement
• Block-level scoping
• Exit Sub Statement
• Terminates execution of a procedure immediately

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IfThenElse Structure

• Enter the following code, starting on line 263
• Parameter Info window

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Considering Selection Structures
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The Nested IfThenElse Structure
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Coding a Nested IfThenElse Structure
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Coding a Nested IfThenElse Structure

• In the code window, delete lines 240 through 251
• Starting on line 259, enter the following code

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Logical Operators

• The Not Logical Operator
• The And Logical Operator
• The Or Logical Operator
• The Xor Logical Operator
• Other Logical Operators
• AndAlso
• OrElse

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Combining Logical Operators

• If XgtY Or TD And Hlt3 Or Not YR Then
• intCount intCount 1
• End If
• Rules of precedence
• Arithmetic operators
• Relational operators
• Not operators
• And/AndAlso operators
• Or/OrElse or Xor operators

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The Effect of Parentheses in the Evaluation of
Compound Conditions

• Parentheses can be used to change the order of
  precedence
• Avoid ambiguity and group conditions with a
  desired logical operator
• (CgtD And S4) Or (XltY And T5)

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Coding with a Logical Operator and String
Expressions
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Coding with a Logical Operator and String
Expressions

• Concatenation () operator
• strErrorMessage Customers with this credit
  rating may only borrow strMoney
• The plus sign () can be used instead of the ()
  operator

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Coding with a Logical Operator and String
Expressions

• Enter the following code, starting on line 272

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The Select Case Structure

• Used to implement an extension of the
  IfThenElse structure

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Coding a Select Case Statement
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Coding a Select Case Statement

• Enter the following code, starting on line 284

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Modifying a Parameter in a Function Call

• The function call to the Pmt function currently
  accepts the dblRate variable as the interest rate
  parameter
• This does not take into account the customers
  credit rating
• In line 300, click between the letters l and R in
  the dblRate parameter in the Pmt function call
  and enter Adjusted to change the parameter name

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Saving and Testing the Project

• Click the Save All button on the Standard toolbar
• Click the Start button on the Visual Basic .NET
  Standard toolbar
• Enter 13000 for the Loan amount. Enter 10.25 for
  the Current interest rate in the second
  NumericUpDown control. Click the Compute Payment
  button
• The No Credit Rating message box should display

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Saving and Testing the Project

• Click the OK button. Click the Credity rating
  box arrow and then select B Good in the Credit
  rating drop-down list. Click the Compute Payment
  button
• The resulting output should display 284.44
• Click the Close button on the Automobile Loan
  Calculator application window title bar

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Document the Application and Quit Visual Basic
.NET

• Prepare printouts of your project, as
  demonstrated in Chapter 2
• Click the Visual Basic .NET Close button

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Summary

• Use the ComboBox control
• Use the IfThenElse structure
• Use a nested IfThenElse structure
• Use the Select Case structure
• Validate user input

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Summary

• Use the MessageBox class
• Use the string concatenation in code
• Use relational operators in code
• Use logical operators in code

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Chapter 5 Complete