1. CHAPTER 6
Loop Structures

2. Objectives Add a MenuStrip object Use the InputBox function
Display data using the ListBox object
Understand the use of counters and accumulators
Understand the use of compound operators
Chapter 6: Loop Structures

3. Objectives Repeat a process using a For…Next loop
Repeat a process using a Do loop
Avoid infinite loops
Prime a loop
Validate data
Chapter 6: Loop Structures

4. Objectives Create a nested loop Select the best type of loop
Debug using DataTips at breakpoints
Publish a finished application using ClickOnce technology
Chapter 6: Loop Structures

5. Introduction
A fundamental process in a computer program is to repeat a series of instructions either while a condition is true (or not true) or until a condition is true (or not true)
The process of repeating a set of instructions while a condition is true or until a condition is true is called looping
Another term for looping is iteration
Chapter 6: Loop Structures

6. MenuStrip Object
A menu bar is a strip across the top of a window that contains one or more menu names
A menu is a group of commands, or items, presented in a list
Chapter 6: Loop Structures

7. MenuStrip Object
With a Windows Form object open in the Visual Studio window, scroll in the Toolbox until the Menus & Toolbars subcategory is visible. If the subcategory is not open, click the + sign next to the Menus & Toolbars subcategory name. Drag the MenuStrip .NET component from the Menus & Toolbars subcategory in the Toolbox to the Windows Form object
Release the mouse button
With the MenuStrip object selected, scroll in the Properties window until the (Name) property is visible. Change the MenuStrip object name to mnuHighwayRadarCheckpoint
Chapter 6: Loop Structures

8. MenuStrip Object
Click the Type Here box on the menu bar. Type &File to identify the File menu, and then press the ENTER key
Click File in the MenuStrip object to select it, scroll in the Properties window to the (Name) property, and then change the name to mnuFileMenu
To add a menu item to the File menu, click the Type Here box below the File menu name. Type &Clear and then press ENTER to create a new menu item named Clear with C as the hot key
On the File menu, click Clear to select it, scroll in the Properties window until the (Name) property is visible, and then change the name to mnuClearItem
Chapter 6: Loop Structures

9. MenuStrip Object
Chapter 6: Loop Structures

10. Event Handlers for Menu Items
In Design view, double-click the Exit menu item to open the code editing window
Using IntelliSense, enter the Close procedure call to close the window and terminate the application
Chapter 6: Loop Structures

11. Standard Items for a Menu
Visual Basic 2005 contains an Action Tag that allows you to create a full standard menu bar commonly provided in Windows programs
Action tags provide a way for you to specify a set of actions, called smart actions, for an object as you design a form
With a new Windows Form object open, drag the MenuStrip .NET component onto the Windows Form object. Click the Action Tag on the MenuStrip object
Click Insert Standard Items on the MenuStrip Tasks menu
Click File on the menu bar to view the individual menu items and their associated icons on the File menu
Chapter 6: Loop Structures

12. Standard Items for a Menu
Chapter 6: Loop Structures

13. InputBox Function
The InputBox function displays a dialog box that consists of a message asking for input, an input area, a title, an OK button, and a Cancel button
When the user enters the text and clicks the OK button, the InputBox function returns this text as a string
If the user clicks the Cancel button, the function returns a null string ("")
Chapter 6: Loop Structures

14. InputBox Object Default Value
The InputBox object can be assigned a default value
Chapter 6: Loop Structures

15. InputBox Object for Highway Radar Checkpoint Application
Chapter 6: Loop Structures

16. Displaying Data Using the ListBox Object
Drag the ListBox object from the Toolbox to the Windows Form object where you want to place the ListBox object. When the pointer is in the correct location, release the left mouse button
With the ListBox object selected, scroll in the Properties window to the (Name) property. Name the ListBox object lstRadarSpeed
Chapter 6: Loop Structures

17. Displaying Data Using the ListBox Object
Chapter 6: Loop Structures

18. Adding Items During Design
Assume the lstStores ListBox object already has been placed and named on the Windows Form object. Select the ListBox object on the Windows Form object and then click the Items property in the Properties window
Click the ellipsis button in the right column of the Items property
Click in the String Collection Editor window. Type the following items to represent popular retail stores, pressing ENTER at the end of each line:
Abercrombie & Fitch
Aeropostale
American Eagle
Express
Hollister
Click the OK button
Chapter 6: Loop Structures

19. Adding Items During Design
Chapter 6: Loop Structures

20. SelectedItem Property
Chapter 6: Loop Structures

21. Accumulators, Counters, and Compound Operators
A variable that contains an accumulated value such as the total of all the speeds is called an accumulator
A variable that always is incremented by a constant value is called a counter
How many vehicle speeds the user has entered
Chapter 6: Loop Structures

22. Accumulators, Counters, and Compound Operators
A compound operator allows you to add, subtract, multiply, divide, use modulus or exponents, or concatenate strings, storing the result in the same variable
Chapter 6: Loop Structures

23. Accumulators, Counters, and Compound Operators
Chapter 6: Loop Structures

24. Accumulators, Counters, and Compound Operators
Chapter 6: Loop Structures

25. Using Loops to Perform Repetitive Tasks
In the Highway Radar Checkpoint application, the user enters up to 10 vehicle speeds using the InputBox function
The repetitive process of entering 10 vehicle speeds can be coded within a loop to simplify the task with fewer lines of code
Each repetition of the loop is called an iteration
Chapter 6: Loop Structures

26. Repeating a Process Using the For…Next Loop
You can use a For...Next loop when a section of code is to be executed an exact number of times
Figure 6-42
Chapter 6: Loop Structures

27. Repeating a Process Using the For…Next Loop
Figures 6-43 and 6-44
Chapter 6: Loop Structures

28. Step Value in a For…Next Loop
A Step value is the value in a For...Next loop that is added to or subtracted from the beginning value on each iteration of the loop
Default step value is 1
Can be positive or negative, contain decumals, or include variables and mathematical expressions
Figure 6-45
Chapter 6: Loop Structures

29. Entering the For…Next Loop Code
Figure 6-49 and 6-53
Chapter 6: Loop Structures

30. Repeating a Process Using a Do Loop
In a Do loop, the body of the loop is executed while or until a condition is true or false
The Do While loop executes as long as the condition is true
The Do Until loop executes until the condition becomes true
A top-controlled loop is tested before the loop is entered
Body might not be executed
Bottom-controlled loops test the condition at the bottom of the loop, so the body of a bottom-controlled loop is executed at least once
Body executes at least once
Chapter 6: Loop Structures

31. Top-Controlled Do While Loops
A top-controlled Do While loop begins with the keywords Do While. Next, the condition is specified
The body of the loop contains the instructions that are executed as long as the condition is true
A loop that does not end is called an infinite loop
Figure 6-56
Chapter 6: Loop Structures

32. Top-Controlled Do While Loops
Chapter 6: Loop Structures

33. Entering a Do Loop Using IntelliSense
In the code editing window, enter the intScore variable declaration and then press the ENTER key. Type Do While, a space, and then press CTRL+SPACEBAR to display the IntelliSense list. Type intS to highlight intScore in the list
Type < 5 and then press the ENTER key.
Press CTRL+SPACEBAR to display the IntelliSense list. Type intS to highlight the intScore variable. Complete the statement by typing += 1 and then pressing the ENTER key. Press the DELETE key to delete the blank line
Chapter 6: Loop Structures

34. Entering a Do Loop Using IntelliSense
Chapter 6: Loop Structures

35. Bottom-Controlled Do While Loop
A bottom-controlled loop works the same way as the top-controlled Do While loop
The body of the loop is executed before the condition is checked the first time, guaranteeing at least one iteration of a loop will be completed
Chapter 6: Loop Structures

36. Bottom-Controlled Do While Loop
Chapter 6: Loop Structures

37. Do Until Loops
Chapter 6: Loop Structures

38. User Input Loops
Do loops often are written to end the loop when a certain value is entered by the user, or the user performs a certain action such as clicking the Cancel button in an input box
Chapter 6: Loop Structures

39. Avoiding Infinite Loops
An infinite loop is a loop that never ends
Chapter 6: Loop Structures

40. Priming the Loop
Starting a loop with a preset value in the variable(s) tested in the condition is called priming the loop
Chapter 6: Loop Structures

41. Validating Data
Chapter 6: Loop Structures

42. Creating a Nested Loop
Any loop can be placed within another loop under the following conditions:
Interior loops must be completely contained inside the outer loop
Must have a different control variable
Chapter 6: Loop Structures

43. Selecting the Best Loop
Use a Do loop if the number of repetitions is unknown and is based on a condition changing; a For...Next loop is best if the exact number of repetitions is fixed
If a loop condition must be tested before the body of the loop is executed, use a top-controlled Do While or Do Until loop. If the instructions within a loop must be executed one time regardless of the status of a condition, use a bottom-controlled Do While or Do Until loop
Use the keyword While if you want to continue execution of the loop while the condition is true. Use the keyword Until if you want to continue execution until the condition is true
Chapter 6: Loop Structures

44. Using a DataTip with Breakpoints
Resolving defects in code is called debugging
A good way to collect information is to pause the execution of the code where a possible error could occur
Breakpoints are stop points placed in the code to tell the Visual Studio 2005 debugger where and when to pause the execution of the application
While in break mode, you can examine the values in all variables that are within the scope of execution through the use of DataTips
Chapter 6: Loop Structures

45. Using a DataTip with Breakpoints
With the program open in the code editing window, right-click line 49, which contains the code where you want to set a breakpoint, and then point to Breakpoint on the shortcut menu
Click Insert Breakpoint on the submenu
To run and test the program with the breakpoint, click the Start Debugging button on the Standard toolbar
Click the Enter Speed button. Type 75 as the speed of the first vehicle
Click the OK button in the input box
Chapter 6: Loop Structures

46. Using a DataTip with Breakpoints
Point to the variable decVehicleSpeed on line 49
You can view the value in any other variable within execution scope by pointing to that variable. To illustrate, point to the variable decTotalOfAllSpeeds on line 49
Continue the program by clicking the Continue button on the Standard toolbar. Notice that the Continue button is the same as the Start Debugging button
Point to the decTotalOfAllSpeeds variable
Chapter 6: Loop Structures

47. Using a DataTip with Breakpoints
Chapter 6: Loop Structures

48. Using a DataTip with Breakpoints
To remove a breakpoint, right-click the statement containing the breakpoint, and then point to Breakpoint on the shortcut menu
Click Delete Breakpoint on the Breakpoint submenu
Chapter 6: Loop Structures

49. Publishing an Application with Click Once Deployment
After an application is completely debugged and working properly, you can deploy the project
Deploying a project means placing an executable version of the program on your hard disk, on a Web server, or on a network server
When programming using Visual Basic 2005, you can create a deployed program by using ClickOnce Deployment
The deployed version of the program you create can be installed and executed on any computer that has the .NET framework installed
Chapter 6: Loop Structures

50. Publishing an Application with ClickOnce Deployment
With the program open, click Build on the menu bar
Click Publish Radar on the Build menu
Change the default location from publish\ to a file location. To publish to a USB drive, type the drive letter. In this example, enter e: for a USB drive
Click the Next button. If necessary, click the From a CD-ROM or DVDROM radio button
Click the Next button. If necessary, click the The application will not check for updates radio button
Chapter 6: Loop Structures

51. Publishing an Application with ClickOnce Deployment
Click the Next button
Click the Finish button
To view the finished result, minimize the Visual Studio window, and then double-click the My Computer icon on the desktop. Double-click the USB drive icon to view the published installation folder
To install the application, double-click the setup file
After installation, the program will run. To run the installed application again, click the Start button on the Windows taskbar. Point to All Programs, point to Radar on the All Programs menu, and then click Radar on the Radar submenu
Chapter 6: Loop Structures

52. Publishing an Application with ClickOnce Deployment
Chapter 6: Loop Structures

53. Program Design
Chapter 6: Loop Structures

54. Program Design
Chapter 6: Loop Structures

55. Event Planning Document
Chapter 6: Loop Structures

56. Summary Add a MenuStrip object Use the InputBox function
Display data using the ListBox object
Understand the use of counters and accumulators
Understand the use of compound operators
Chapter 6: Loop Structures

57. Summary Repeat a process using a For…Next loop
Repeat a process using a Do loop
Avoid infinite loops
Prime a loop
Validate data
Chapter 6: Loop Structures

58. Summary Create a nested loop Select the best type of loop
Debug using DataTips at breakpoints
Publish a finished application using ClickOnce technology
Chapter 6: Loop Structures

59. CHAPTER 6 COMPLETE
Loop Structures