1. Chapter 4 Decisions and Conditions
Programming In
Visual Basic .NET

2. If Statements Used to make decisions
If true, only the Then clause is executed, if false, only Else clause, if present, is executed
Block If…Then…Else must always conclude with End If
Then must be on same line as If or ElseIf
End If and Else must appear alone on a line
Note: ElseIf is 1 word, End If is 2 words
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3. If…Then…Else – General Form
If (condition) Then statement(s)
[ElseIf (condition) Then
statement(s)]
[Else
End If
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4. If…Then…Else - Example
unitsDecimal = Decimal.Parse(unitsTextBox.Text)
If unitsDecimal < 32D Then freshmanRadioButton.Checked = True
Else freshmanRadioButton.Checked = False
End If
© 2005 by The McGraw-Hill Companies, Inc. All rights reserved.

5. Conditions Test in an If statement is based on a condition
Six relational operators are used for comparison
Negative numbers are less than positive numbers
An equal sign is used to test for equality
Strings can be compared, enclose strings in quotes (see Page 142 for ANSI Chart, case matters)
JOAN is less than JOHN
HOPE is less than HOPELESS
Numbers are always less than letters
300ZX is less than Porsche
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6. The Six Relational Operators
Greater Than >
Less Than <
Equal To =
Not Equal To <>
Greater Than or Equal To >=
Less Than or Equal to <=
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7. ToUpper and ToLower Methods
Use ToUpper and ToLower methods of the String class to return the uppercase or lowercase equivalent of a string, respectively
If nameTextBox.Text.ToUpper( ) = "Basic" Then
' Do something.
End If
© 2005 by The McGraw-Hill Companies, Inc. All rights reserved.

8. Compound Conditions Join conditions using logical operators
Or If one or both conditions True, entire condition is True
And Both conditions must be True for entire condition to be True
Not Reverses the condition, a True condition will evaluate False and vice versa
© 2005 by The McGraw-Hill Companies, Inc. All rights reserved.

9. Compound Condition Examples
If maleRadioButton.Checked And _
Integer.Parse(ageTextBox.Text) < 21 Then
minorMaleCountInteger += 1
End If
If juniorRadioButton.Checked Or seniorRadioButton.Checked Then
upperClassmanInteger += 1
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10. Combining And and Or Example
If saleDecimal > Or discountRadioButton.Checked _
And stateTextBox.Text.ToUpper( ) <> "CA" Then ' Code here to calculate the discount.
End If
© 2005 by The McGraw-Hill Companies, Inc. All rights reserved.

11. Nested If Statements If tempInteger > 32 Then
commentLabel.Text = "Hot"
Else
commentLabel.Text = "Moderate"
End If
commentLabel.Text = "Freezing"
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12. Using If Statements with Radio Buttons & Check Boxes
Instead of coding the CheckedChanged events, use If statements to see which are selected
Place the If statement in the Click event for a Button, such as an OK or Apply button
Private Sub testButton_Click(ByVal sender As System.Object, _ By Val e As System.EventArgs) Handles testButton.Click
' Test the value of the check box.
If testCheckBox.Checked Then
messageLabel.Text = "Check box is checked"
End If
End Sub
© 2005 by The McGraw-Hill Companies, Inc. All rights reserved.

13. Enhancing Message Boxes
For longer, more complex messages, store the message text in a String variable and use that variable as an argument of the Show method
VB will wrap longer messages to a second line
Include ControlChars to control the line length and position of the line break
© 2005 by The McGraw-Hill Companies, Inc. All rights reserved.

14. ControlChars Constants (p 152)
Constant Description
CR Carriage Return
CRLF Carriage Return + Line Feed
NewLine Carriage Return + Line Feed
Tab Tab Character
NullChar Character with a Value of Zero
Quote Quotation Mark Character
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15. Message Box - Multiple Lines of Output
ControlChars.NewLine
Used to force to next line
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16. Message String Example
Dim formattedTotalString As String
Dim formattedAvgString As String
Dim messageString As String
formattedTotalString = totalSalesDecimal.ToString("N")
formattedAvgString = averageSalesDecimal.ToString("N")
messageString = "Total Sales: " & formattedTotalString _
& ControlChars.NewLine & "Average Sale: " & _
formattedAvgString
MessageBox.Show(messageString, "Sales Summary", _
MessageBoxButtons.OK)
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17. Displaying Multiple Buttons
Use MessageBoxButtons constants to display more than one button in the Message Box
Message Box's Show method returns a DialogResult object that can be checked to see which button the user clicked
Declare a variable to hold an instance of the DialogResult type to capture the outcome of the Show method
© 2005 by The McGraw-Hill Companies, Inc. All rights reserved.

18. Message Box - Multiple Buttons
MessageBoxButtons.YesNo
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19. Declaring a Variable for the Method Return
Dim whichButtonDialogResult As DialogResult
whichButtonDialogResult = MessageBox.Show _
("Clear the current order figures?", "Clear Order", _ MessageBoxButtons.YesNo, MessageBoxIcon.Question)
If whichButtonDialogResult = DialogResult.Yes Then
' Code to clear the order.
End If
© 2005 by The McGraw-Hill Companies, Inc. All rights reserved.

20. Specifying a Default Button and Options
Use a different signature for the Message Box Show method to specify a default button
Add the MessageBoxDefaultButton argument after the MessageBoxIcons argument
Set message alignment with MessageBoxOptions argument
© 2005 by The McGraw-Hill Companies, Inc. All rights reserved.

21. Input Validation
Check to see if valid values were entered by user before beginning calculations
Check for a range of values (reasonableness)
If Integer.Parse(hoursTextBox.Text) > 10 Then
MessageBox.Show("Too many hours")
Check for a required field (not blank)
If nameTextBox.Text <> "" Then ...
© 2005 by The McGraw-Hill Companies, Inc. All rights reserved.

22. Performing Multiple Validations
Use nested If statement to validate multiple values on a form
Examine example on Page 156
Use Case structure to validate multiple values
Simpler and clearer than nested If
No limit to number of statements that follow a Case statement
When using a relational operator must use the word Is
Use the word To to indicate a range of constants
© 2005 by The McGraw-Hill Companies, Inc. All rights reserved.

23. Sharing an Event Procedure
Add events to the Handles clause at the top of an event procedure
Allows the procedure to respond to events of other controls
Key to using a shared event procedure is the sender argument
Cast (convert) sender to a specific object type using the CType function
© 2005 by The McGraw-Hill Companies, Inc. All rights reserved.

24. Calling Event Procedures
Reusable code
General Form
[Call] ProcedureName ( )
Keyword Call is optional and rarely used
Examples
Call clearButton_Click (sender, e) OR
clearButton_Click (sender, e)
© 2005 by The McGraw-Hill Companies, Inc. All rights reserved.

25. Debugging (p 169) Debug Menu Debug Toolbar
Toggle BreakPoints on/off by clicking Editor's gray left margin indicator
Step through Code, Step Into, Step Over
View the values of properties, variables, mathematical expressions, and conditions
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26. Debugging (cont.) Output Window Locals Window Autos Window
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27. Debug Menu and Toolbar
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28. Writing to the Output Window
Debug.WriteLine(TextString)
Debug.WriteLine(Object)
Debug.WriteLine("calculateButton procedure entered")
Debug.WriteLine(quantityTextBox)
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29. Breakpoints
Toggle Breakpoints On/Off by clicking in Editor's gray left margin indicator
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30. Checking the Current Value of Expressions
Place mouse pointer over variable or property to view current value
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31. Locals Window
Shows values of local variables that are within scope of current statement
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32. Autos Window
Automatically adjusts to show variables and properties that appear in previous and next few lines
© 2005 by The McGraw-Hill Companies, Inc. All rights reserved.