1. CHAPTER FIVE
Decision Structures

2. Objectives Use the GroupBox object
Place RadioButton objects in applications
Display a message box
Make decisions using If…Then statements
Make decisions using If…Then…Else statements
Make decisions using nested If statements
Chapter 5: Decision Structures

3. Objectives Make decisions using logical operators
Make decisions using Case statements
Insert code snippets
Test input to ensure a value is numeric
Chapter 5: Decision Structures

4. Preview the Chapter Project
Chapter 5: Decision Structures

5. Using the GroupBox Object
Drag the GroupBox object in the Containers category of the Toolbox over the Form object to the approximate location where you want to place the GroupBox object
When the mouse pointer is in the correct location, release the left mouse button. With the GroupBox object selected, scroll in the Properties window to the (Name) property. Double-click in the right column of the (Name) property and then enter the name grpWoodType
Click to the right of the Size property of the GroupBox object and enter 125,100 as the size. Change the Font property to Goudy Old Style, Regular, Size 12. Change the BackColor property to White
Chapter 5: Decision Structures

6. Using the GroupBox Object
Chapter 5: Decision Structures

7. Using the GroupBox Object
Chapter 5: Decision Structures

8. Adding the RadioButton Objects
Drag and drop one RadioButton object from the Toolbox into the GroupBox object on the Form object.Drag a second RadioButton object from the Toolbox into the GroupBox object, using blue snap lines to align and separate the RadioButton objects vertically
Release the left mouse button to place the RadioButton object on the Form object within the GroupBox object. Using the same technique, add a third RadioButton object
Chapter 5: Decision Structures

9. Adding the RadioButton Objects
Name the RadioButton objects by selecting a RadioButton object, double-clicking in the right column of the (Name) property in the Properties window, and entering the name. The names for the radio buttons, from top to bottom, should be radPine, radOak, and radCherry
Change the Text property for each RadioButton by double-clicking in the right column of the Text property and typing Pine for the first RadioButton, Oak for the second RadioButton and Cherry for the third RadioButton
Chapter 5: Decision Structures

10. Adding the RadioButton Objects
Chapter 5: Decision Structures

11. Adding the RadioButton Objects
Chapter 5: Decision Structures

12. Windows Application Container Objects
Chapter 5: Decision Structures

13. Displaying a Message Box
Chapter 5: Decision Structures

14. Displaying a Message Box
Chapter 5: Decision Structures

15. Displaying a Message Box
Chapter 5: Decision Structures

16. Displaying a Message Box
Chapter 5: Decision Structures

17. Displaying a Message Box
Chapter 5: Decision Structures

18. Message Box IntelliSense
In the code editing window, inside the event handler you are coding, type msg to display MsgBox in the IntelliSense list
Press the Tab key to select MsgBox from the IntelliSense list. Type the following text: (“You have been disconnected from the Internet”, m)
Select the MsgBoxStyle.AbortRetryIgnore argument by pressing the UP ARROW until the correct argument is highlighted.Type a comma.Then type "ISP” and a right parenthesis
Click the Start Debugging button on the Standard toolbar
Chapter 5: Decision Structures

19. Message Box IntelliSense
Chapter 5: Decision Structures

20. Displaying a Message Box
Chapter 5: Decision Structures

21. Making Decisions with Conditional Statements: Using an If…Then Statement
A decision structure is one of the three fundamental control structures used in computer programming
When a condition is tested in a Visual Basic program, the condition either is true or false
Chapter 5: Decision Structures

22. Relational Operators
Chapter 5: Decision Structures

23. Relational Operators
With the insertion point located in the correct location in the code, type if and then press the SPACEBAR
Type inta to select the variable named intAge in the IntelliSense list. Then, type >=18 as the condition to be tested. Press the ENTER key
On the blank line, enter the statement that should be executed when the condition is true. To place the message, “You are old enough to vote” in the Text property of the lblVotingEligibility Label object, insert the code shown in Figure 5-33 on page 315. Remember to use IntelliSense to reference the lblVotingEligibility Label object
Chapter 5: Decision Structures

24. Relational Operators
Chapter 5: Decision Structures

25. Comparing Strings
A string value comparison compares each character in two strings, starting with the first character in each string
Chapter 5: Decision Structures

26. Comparing Different Data Types
Every type of data available in Visual Basic can be compared
Different numeric types can be compared to each other
A single string character can be compared to a Char data type
Chapter 5: Decision Structures

27. Using the If…Then…Else Statement
Chapter 5: Decision Structures

28. Using the If…Then…ElseIf Statement
Chapter 5: Decision Structures

29. Nested If Statements
Chapter 5: Decision Structures

30. Nested If Statements
Chapter 5: Decision Structures

31. Matching If, Else, and End If Entries
If statements must be fully contained within the outer If statement
Place the correct statements with the correct If and Else statements within the nested If statement
This illustration shows incorrect logic
Chapter 5: Decision Structures

32. Testing the Status of a RadioButton Object in Code
Chapter 5: Decision Structures

33. Block-Level Scope
Scope is defined by where the variable is declared within a program
Within an event handler, an If…Then…Else statement is considered a block of code
Variables can be declared within a block of code
The variable can be referenced only within the block of code where it is declared
Chapter 5: Decision Structures

34. Using Logical Operators
When more than one condition is included in an If...Then...Else statement, the conditions are called a compound condition
Chapter 5: Decision Structures

35. Using the And Logical Operator
Chapter 5: Decision Structures

36. Using the Or Logical Operator
Chapter 5: Decision Structures

37. Using the Not Logical Operator
Chapter 5: Decision Structures

38. Other Logical Operators
Chapter 5: Decision Structures

39. Order of Operations for Logical Operators
Chapter 5: Decision Structures

40. Select Case Statement
In some programming applications, different operations can occur based upon the value in a single field
Chapter 5: Decision Structures

41. Select Case Statement
Chapter 5: Decision Structures

42. Select Case Test Expressions
Chapter 5: Decision Structures

43. Using Relational Operators in a Select Case Statement
Chapter 5: Decision Structures

44. Using Ranges in Select Case Statements
Chapter 5: Decision Structures

45. Selecting Which Decision Structure to Use
You might be faced with determining if you should use the Select Case statement or the If...Then...ElseIf statement to solve a problem
Generally, the Select Case statement is most useful when more than two or three values must be tested for a given variable
The If...Then...ElseIf statement is more flexible
More than one variable can be used in the comparison
Compound conditions with the And, Or, and Not logical operators can be used
Chapter 5: Decision Structures

46. Code Snippets
Right-click the line in the code editing window where you want to insert the snippet
Click Insert Snippet on the shortcut menu
Double-click the folder Code Patterns - If, For Each,Try Catch, Property, etc, which contains commonly used code such as the If Then Else statement
Double-click the Conditionals and Loops folder because an If...Then...Else statement is a conditional statement
Double-click the If...Else...End If Statement code snippet
Chapter 5: Decision Structures

47. Code Snippets
Chapter 5: Decision Structures

48. Code Snippets
Chapter 5: Decision Structures

49. Validating Data
Developers should anticipate that users will enter invalid data
Developers must write code that will prevent the invalid data from being used in the program to produce invalid output
Chapter 5: Decision Structures

50. Testing Input to Determine If the Value Is Numeric
The Visual Basic IsNumeric function can check the input value to determine if the value can be converted into a numeric value such as an Integer or Decimal data type
Chapter 5: Decision Structures

51. Checking for a Positive Number
Chapter 5: Decision Structures

52. Program Design
Chapter 5: Decision Structures

53. Program Design
Chapter 5: Decision Structures

54. Program Design
Chapter 5: Decision Structures

55. Chapter Summary Use the GroupBox object
Place RadioButton objects in applications
Display a message box
Make decisions using If…Then statements
Make decisions using If…Then…Else statements
Make decisions using nested If statements
Chapter 5: Decision Structures

56. Chapter Summary Make decisions using logical operators
Make decisions using Case statements
Insert code snippets
Test input to ensure a value is numeric
Chapter 5: Decision Structures

57. CHAPTER FIVE COMPLETE
Decision Structures