CHAPTER SIX

1. CHAPTER SIX 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. Preview the Chapter Project Chapter 6: Loop Structures

7. 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

8. MenuStrip Object • With a Windows Form object open in the Visual Studio window, scroll in the Toolbox until the Menus & Toolbars category is visible. If the category is not open, click the expand icon (right-pointing triangle) next to the Menus & Toolbars category name. Drag the MenuStrip .NET component from the Menus & Toolbars category 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

9. 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 mnuFile • 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

10. MenuStrip Object Chapter 6: Loop Structures

11. MenuStrip Object Chapter 6: Loop Structures

12. 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

13. Event Handlers for Menu Items Chapter 6: Loop Structures

14. Standard Items for a Menu • Visual Basic 2010 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

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

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

17. 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

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

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

20. 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

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

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

23. 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

24. Adding Items During Design Chapter 6: Loop Structures

25. Adding Items During Design Chapter 6: Loop Structures

26. SelectedItem Property Chapter 6: Loop Structures

27. 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

28. 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

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

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

31. 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

32. 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 Chapter 6: Loop Structures

33. Repeating a Process Using the For…Next Loop Chapter 6: Loop Structures

34. 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 Chapter 6: Loop Structures

35. Entering the For…Next Loop Code Chapter 6: Loop Structures

36. Entering the For…Next Loop Code Chapter 6: Loop Structures

37. 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

38. 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 Chapter 6: Loop Structures

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

40. 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 an IntelliSense list is displayed. Type ints to highlight intScore in the list • Type < 5 and then press the ENTER key. • 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

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

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

43. 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

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

45. Do Until Loops Chapter 6: Loop Structures

46. 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

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

48. 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

49. Validating Data Chapter 6: Loop Structures

50. 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