Microsoft Visual Basic 2005 CHAPTER 6. Loop Structures

Transcription

1 Microsoft Visual Basic 2005 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 2

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 3

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 4

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 5

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 6

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 7

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 8

9 MenuStrip Object Chapter 6: Loop Structures 9

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 10

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 11

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

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 13

14 InputBox Object Default Value The InputBox object can be assigned a default value Declare the variable globally Default Value assigned to a variable Chapter 6: Loop Structures 14

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

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 16

17 Displaying Data Using the ListBox Object LST for LIST Chapter 6: Loop Structures End One 17

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 18

19 Adding Items During Design Chapter 6: Loop Structures 19

20 SelectedItem Property Chapter 6: Loop Structures 20

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 21

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 22

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

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

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 25

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 26

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

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 28

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

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 30

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 31

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

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 33

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

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 35

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

37 Do Until Loops Chapter 6: Loop Structures 37

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 38

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

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 40

41 Validating Data Chapter 6: Loop Structures 41

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 42

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 43

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 44

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 45

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 46

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

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 48

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 49

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 50

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 51

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

53 Program Design Chapter 6: Loop Structures 53

54 Program Design Chapter 6: Loop Structures 54

55 Event Planning Document Chapter 6: Loop Structures 55

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 56

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 57

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 58

59 Microsoft Visual Basic 2005 CHAPTER 6 COMPLETE Loop Structures