1. Tutorial 4 The Selection Structure

2. The If…Then…Else Statement Lesson A Objectives
After completing this lesson, you will be able to:
Write pseudocode for the selection structure
Create a flowchart to help you plan an application’s code
Write an If…Then…Else statement
Write code that uses comparison operators and logical operators
Use the UCase and LCase functions
Tutorial 4: The Selection Structure

3. The Selection Structure
Use to make a decision or comparison and then, based on the result of that decision or comparison, to select one of two paths
You use the selection structure, also called the decision structure, when you want a program to make a decision or comparison and then, based on the result of the decision or comparison, select a particular set of tasks to perform
The condition must result in either a true (yes) or false (no) answer
If the condition is true, the program performs one set of tasks. If the condition is false, there may or may not be a different set of tasks to perform.
Tutorial 4: The Selection Structure

4. Writing Pseudocode for If and If/Else Selection Structures
An If structure contains only one set of instructions which are processed when the condition is true
If condition is true Then
perform these tasks
End If
Perform these tasks
whether condition is true
or false
An If/Else structure contains two sets of instructions: one set is processed when the condition is true and the other set is processed when the condition is false
If condition is true then
perform these tasks
Else
End If
Perform these tasks
whether condition is true
or false
Tutorial 4: The Selection Structure

5. Flowchart Symbols start/stop oval process rectangle
input/output parallelogram
selection/repetition diamond
symbols are connected by flowlines
Tutorial 4: The Selection Structure

6. Selection Structure Flowcharts
Tutorial 4: The Selection Structure

7. Coding the If and If/Else Selection Structures
The items in square brackets ([ ]) in the syntax are optional
You do not need to always include the Else portion
Words in bold, however, are essential components of the statement
Items in italics indicate where the programmer must supply information pertaining to the current application
The set of statements contained in the true path, as well as the set of statements contained in the false path, are referred to as a statement block
Tutorial 4: The Selection Structure

8. Coding the If and If/Else Selection Structures
If condition Then
instructions when the condition is true
End If
[instructions when the condition is true]
[Else
[instructions when the condition is false]]
Tutorial 4: The Selection Structure

9. Comparison Operators =
Is equal to
>
Is Greater Than
>=
Is Greater Than or Equal to
<
Is Less Than
<=
Is Less Than or Equal to
<>
Is Not Equal to
Comparison operators are evaluated from left to right, and are evaluated after any mathematical operators
Tutorial 4: The Selection Structure

10. Expressions Containing Relational Operators
< 5 * 2
5 * 2 is evaluated first, giving 10
is evaluated second, giving 13
13 < 10 is evaluated last, giving false
7 > 3 * 4 / 2
3 * 4 is evaluated first, giving 12
12 / 2 is evaluated second, giving 6
7 > 6 is evaluated last, giving true
All expressions containing a relational operator will result in either a true or false answer only
Tutorial 4: The Selection Structure

11. Using a Comparison Operator
Dim intFirst, intSecond As Integer
If (intFirst > intSecond) Then
Dim intTemp As Integer
intTemp = intFirst
intFirst = intSecond
intFirst = intTemp
End If
Block-level
Variable
Tutorial 4: The Selection Structure

12. If the answer is False Dim strOperation As String
Dim intFirst, intSecond, intAnswer As Integer
If strOperation = "A" Then
intAnswer = intFirst + intSecond
Else
intAnswer = intFirst - intSecond
End If
Tutorial 4: The Selection Structure

13. Logical Operators
Not
Reverses the truth value of condition; false becomes true and true becomes false. 1
And
All conditions connected by the And operator must be true for the compound condition to be true. 2
AndAlso
All conditions connected by the AndAlso operator must be true for the compound condition to be true. Or
Only one of the conditions connected by the Or operator needs to be true for the compound condition to be true. 3
OrElse
Only one of the conditions connected by the OrElse operator needs to be true for the compound condition to be true.
Xor
Only when one and only one condition connected by Xor is true for the compound condition to be true. 4
Tutorial 4: The Selection Structure

14. Truth Table for Not Operator
Result = Not Condition
If condition is
Value of Result is
True
False
Tutorial 4: The Selection Structure

15. Truth Table for And Operator
Result = condition1 And Condition2
If condition1 is
And condition2 is
Value of Result is
True
False
Tutorial 4: The Selection Structure

16. Expressions Containing the And Logical Operator
3 > 2 is evaluated first, giving true
6 > 5 is evaluated second, giving true
true And true is evaluated last, giving true
10 < 25 And 6 > 5 + 1
5 + 1 is evaluated first, giving 6
10 < 25 is evaluated second, giving true
6 > 6 is evaluated third, giving false
true And false is evaluated last, giving false
Tutorial 4: The Selection Structure

17. Truth Table for AndAlso Operator
Result = condition1 AndAlso Condition2
If condition1 is
And condition2 is
Value of Result is
True
False
(not evaluated)
Tutorial 4: The Selection Structure

18. Expressions Containing the AndAlso Logical Operator
3 < 2 is evaluated first, giving false
6 > 5 is not evaluated
false
10 < 25 AndAlso 6 > 5 + 1
10 < 25 is evaluated first, giving true
5 + 1 is evaluated second, giving 6
6 > 6 is evaluated third, giving false
true And false is evaluated last, giving false
strSales = 12000
strRate = “A”
strRate =“A” AndAlso sngSales > 10000
strRate =“A” is evaluated first, giving true
sngSales > is evaluated second giving true
true AndAlso true gives true
Tutorial 4: The Selection Structure

19. Truth Table for Or Operator
Result = condition1 Or Condition2
If condition1 is
And condition2 is
Value of Result is
True
False
Tutorial 4: The Selection Structure

20. Expressions Containing the Or Logical Operator
3 < 2 is evaluated first, giving false
6 > 5 is evaluated second giving true
false or true gives true
10 < 25 Or 6 > 5 + 1
10 < 25 is evaluated first, giving true
5 + 1 is evaluated second, giving 6
6 > 6 is evaluated third, giving false
true or false is evaluated last, giving true
Tutorial 4: The Selection Structure

21. Truth Table for OrElse Operator
Result = condition1 OrElse Condition2
If condition1 is
And condition2 is
Value of Result is
True
(not evaluated)
False
Tutorial 4: The Selection Structure

22. Expressions Containing the OrElse Logical Operator
3 < 2 is evaluated first, giving false
6 > 5 is evaluated second giving true
false or true gives true
10 < 25 OrElse 6 > 5 + 1
10 < 25 is evaluated first, giving true
6 > is not evaluated
true
strRate1 = “A” : strRate2 = “B”: strTest = “B”
strRate1 = strTest OrElse strRate2 = strTest
strRate1 = strTest is evaluated first, giving false
strRate2 = strTest is evaluated second giving true
false Or true gives true
Tutorial 4: The Selection Structure

23. Truth Table for Xor Operator
Result = condition1 Xor Condition2
If condition1 is
And condition2 is
Value of Result is
True
False
Tutorial 4: The Selection Structure

24. Operator Order of Precedence
Arithmetic Operators
Exponentiation
Negation
Multiplication and division
Integer division
Modulus
Addition and subtraction
Concatenation Operators
Comparison Operators
Logical Operators
Not
And and AndAlse
Or and OrElse
Xor
Tutorial 4: The Selection Structure

25. Using Logical Operators in an If…Then…Else Statement
‘ Using the AndAlso If sngHours >= 0 AndAlso sngHours <= 40 Then
sngPay = sngHours * 10.65
Else
MessageBox.Show("Input Error")
End If
‘Using the OrElse If sngHours < 0 OrElse sngHours > 40 Then
Tutorial 4: The Selection Structure

26. Another Example
‘Test for a character If strLetter = "p" OrElse strLetter = "P" Then
ResultLabel .Text = “Pass"
Else
ResultLabel .Text = “Fail"
End If
Tutorial 4: The Selection Structure

27. The UCase and LCase Functions
In most programming languages, string comparisons are case sensitive--in other words, the letter “A” is not the same as the letter “a”
UCase is a function that converts all characters to Upper Case
strData = UCase(“New York”)
strData now contains “NEW YORK”
LCase is a function the converts all characters to Lower Case
strData = LCase(“New York”)
strData now contains “new york”
Tutorial 4: The Selection Structure

28. The UCase and LCase Functions
Determine if the variable strState is California
If strState =“CA” OrElse strState = “ca” OrElse strState = “cA” OrElse strState = “Ca” Then
Or you can use the UCase function
If UCase(strState) = “CA” Then
Or you can use the ToUpper function
If strState.ToUpper = “CA” Then
Tutorial 4: The Selection Structure

29. The ToUpper and ToLower Methods
‘ An alternative way
If strLetter.ToUpper = "P" Then
ResultLabel .Text = "Pass"
Else
ResultLabel .Text = “Fail"
End If
strData = “New York”
strData = strData.ToUpper
‘strData now contains “NEW YORK”
strDate = strData.ToLower
‘strData now contains “new york”
Tutorial 4: The Selection Structure

30. UCase Function Public Function UCase(ByVal Value As String) As String
Member of: Microsoft.VisualBasic.Strings
Summary:
Returns a String or Char containing the specified string converted to uppercase.
Parameters:
Value: Any valid String or Char expression.
Remarks
Only lowercase letters are converted to uppercase; all uppercase letters and nonletter characters remain unchanged.
Tutorial 4: The Selection Structure

31. String.ToUpper Method Returns a copy of this String in uppercase.
(Object Browser)
Public Function ToUpper() As String
Member of: System.String
Summary:
Returns a copy of this System.String in uppercase, using the casing rules of the current culture.
Return Values:
A System.String in uppercase.
Tutorial 4: The Selection Structure

32. The Monthly Payment Calculator Application Lesson B Objectives
After completing this lesson, you will be able to:
Group objects using a GroupBox control
Calculate a periodic payment using the Pmt function
Create a message box using the MessageBox.Show method
Determine the value returned by a message box
Tutorial 4: The Selection Structure

33. Adding a GroupBox Control to the Form
You use the GroupBox tool in the Toolbox window to add a group box control to the interface
A group box control serves as a container for other controls
You can use a group box control to visually separate related controls from other controls on the form
Place the GroupBox control on the form and drag other controls into it
Page
Page 249 Set TabIndex
Tutorial 4: The Selection Structure

34. Coding the CalcPayButton Click Event Procedure
The CalcPayButton’s Click event procedure is responsible for calculating the monthly payment amount, and then displaying the result in the PaymentLabel control
The pseudocode for the CalcPayButton’s Click event procedure is shown in Figure in the textbook
Tutorial 4: The Selection Structure

35. Tutorial 4: The Selection Structure

36. The Pmt Function
You can use the Visual Basic .NET Pmt function to calculate a periodic payment on either a loan or an investment (page )
Syntax: Function PMT(ByVal Rate As Double, ByVal NPer As Double, ByVal PV As Double, Optional ByVal FV As Double = 0, Optional ByVal Due As DueDate = DueDate.EndOfPeriod) As Double
Example: Pmt(0.05, 3, 9000, 0, DueDate.EndOfPeriod) Pmt(0.06/12, 20 * 12, 0, 40000, DueDate.BegOfPeriod) -Pmt(sngRate / 12, intTerm * 12, sngPrincipal, 0, DueDate.BegOfPeriod)
Tutorial 4: The Selection Structure

37. The MessageBox.Show Method
You can use the Message.Box.Show method to display a
message box that contains text, one or more buttons, and an icon
Overloads Public Shared Function Show( _ ByVal text As String, _ ByVal caption As String, _ ByVal buttons As MessageBoxButtons, _ ByVal icon As MessageBoxIcon, _ ByVal defaultButton As MessageBoxDefaultButton, _ ByVal options As MessageBoxOptions _ ) As DialogResult
MessageBox.Show("Rate should be 1 or greater", _
"Interest rate", _
MessageBoxButtons.OK, _
MessageBoxIcon.Exclamation, _
MessageBoxDefaultButton.Button1)
Tutorial 4: The Selection Structure

38. MessageBoxButtons Member Name Description AbortRetryIgnore
The message box contains Abort, Retry, and Ignore buttons OK
The message box contains an OK button
OKCancel
The message box contains an OK and a Cancel button
RetryCancel
The message box contains Retry and Cancel buttons
YesNo
The message box contains Yes and No button
YesNoCancel
The message box contains Yes, No, and Cancel buttons
Tutorial 4: The Selection Structure

39. MessageBoxIcons Member Name Description Asterisk or Information
a lowercase letter i in a circle
Error or Hand or Stop
a white X in a circle with a red background
Exclamation
an exclamation point in a triangle with a yellow background
None
no symbols
Question
a question mark in a circle
Warning
an exclamation-point in a triangle with a yellow background
Tutorial 4: The Selection Structure

40. MessageBoxDefaultButton
Member Name
Description
Button1
The first button is the default
Button2
The second button is the default
Button3
The third button is the default
Tutorial 4: The Selection Structure

41. MessageBoxOptions Member Name Description DefaultDesktopOnly
The MessageBox is displayed on the active desktop
RightAlign
The MessageBox is right-aligned
RtlReading
The MessageBox text is displayed in right to left order
ServiceNotification
Tutorial 4: The Selection Structure

42. DialogResult Member Name Description Abort
The Abort button was selected
Cancel
The Cancel button was selected
Ignore
The Ignore button was selected No
The No button was selected OK
The OK button was selected
Retry
The Retry button was selected
Yes
The Yes button was selected
After displaying the message box, the MessageBox.Show method waits for the user to choose one of the buttons displayed in the message box. It then closes the message box and returns a number—an integer—that indicates which button the user chose. There is an enumeration that contains constant values for each return. While you can use the integer, it is generally better (and easier to read) to use these built-in constants.
You can store the result of the message box in a variable, intRC (for result code) and then use
If intRC = DialogResult.Yes Then
‘ do the yes code
ElseIf intRC = DialogResult.No Then
‘ do the no code
Tutorial 4: The Selection Structure

43. Completing the Monthly Payment Calculator Application Lesson C Objectives
After completing this lesson, you will be able to:
Specify the keys that a text box will accept
Display the ControlChars constants
Align the text in a label control
Tutorial 4: The Selection Structure

44. Coding the KeyPress Event
Template
Private Sub PrincipalTextBox_KeyPress( _
ByVal sender As Object, _
ByVal e As System.Windows.Forms.KeyPressEventArgs) _
Handles PrincipalTextBox.KeyPress
Setting e.Handled = True will cancel the key
Page 268
Tutorial 4: The Selection Structure

45. ControlChars Class Field Meaning Back Backspace NewLine Same as CrLf
Carriage Return
NullChar
A null
CrLf
Carriage Return and Line Feed
Quote
Double quote
FormFeed
Form Feed
Tab Lf
Line Feed
VerticalTab
Vertical Tab
strText = “Hello” & ControlChars.NewLine & “World”
Tutorial 4: The Selection Structure

46. Aligning Text in a Label Using the TextAlign Property
Member Name
Description
BottomCenter
Content is vertically aligned at the bottom, and horizontally aligned at the center
BottomRight
Content is vertically aligned at the bottom, and horizontally aligned on the right.
MiddleCenter
Content is vertically aligned in the middle, and horizontally aligned at the center.
MiddleLeft
Content is vertically aligned in the middle, and horizontally aligned on the left.
MiddleRight
Content is vertically aligned in the middle, and horizontally aligned on the right.
TopCenter
Content is vertically aligned at the top, and horizontally aligned at the center.
TopLeft
Content is vertically aligned at the top, and horizontally aligned on the left.
TopRight
Content is vertically aligned at the top, and horizontally aligned on the right.
Tutorial 4: The Selection Structure