Microsoft Visual Basic 2012 Loop Structures CHAPTER SIX.

Microsoft Visual Basic 2012

Loop Structures

CHAPTER SIX

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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

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Objectives

►Repeat a process using a For…Next loop►Repeat a process using a Do loop►Avoid infinite loops►Prime a loop►Validate data

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Objectives

►Create a nested loop►Select the best type of loop►Debug using DataTips at breakpoints►Publish a finished application using ClickOnce

technology

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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

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User Interface Design

►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

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►With a Windows Form object open in the Visual Studio window, scroll in the Toolbox to display the Menus & Toolbars category. If the category is not open, tap or click the expand icon (the right-pointing triangle) next to the Menus & Toolbars category name. Drag the MenuStrip .NET component 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 mnuFitness

►Tap or click the Type Here box on the menu bar. Type &File to identify the File menu, and then press the ENTER key

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►Tap or 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, tap or 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, tap or click Clear to select it, scroll in the Properties window until the (Name) property is visible, and then change the name to mnuClear

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Event Handlers for Menu Items

►In Design view, double-tap or double-click the Exit menu item to open the code window

►Using IntelliSense, enter the Close procedure call to close the window and terminate the application

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Inserting Standard Items for a Menu

► Visual Basic 2012 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. Tap or click the Action Tag on the MenuStrip object

► Tap or click Insert Standard Items on the MenuStrip Tasks menu► Tap or click File on the menu bar to view the individual menu items,

their associated icons, and their shortcut keys

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Inserting Standard Items for a Menu

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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 taps or clicks the OK button, the InputBox function returns this text as a string

►If the user taps or clicks the Cancel button, the function returns a null string ("")

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InputBox Function

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Creating the InputBox Object for Fitness Challenge Application

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Displaying Data Using the ListBox Object

►Drag the ListBox object from the Toolbox to where you want to place the ListBox object on the Windows Form 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 lstWeightLoss

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Displaying Data Using the ListBox Object

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Adding ListBox 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 tap or click the Items property in the Properties window

►Tap or click the ellipsis button in the right column of the Items property

►Tap or 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 & FitchAeropostaleAmerican EagleExpressHollister

►Tap or click the OK button

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Adding ListBox Items During Design

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SelectedItem Property

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Accumulators, Counters, and Compound Operators

►A variable that contains an accumulated value such as the total of all the weight loss values is called an accumulator

►A variable that always is incremented by a constant value is called a counter

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►A compound operator allows you to add, subtract, multiply, divide, use modulus or exponents, or concatenate strings, storing the result in the same variable

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Using Loops to Perform Repetitive Tasks

►In the Fitness Challenge application, the user enters weight loss values in an InputBox for up to eight team members

►The repetitive process of entering eight weight loss values can be coded within a loop to simplify the task with fewer lines of code

►Each repetition of the loop is called an iteration

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Repeating a Process Using the For…Next Loop

►You can use a For...Next loop when a section of code should be executed an exact number of times

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Repeating a Process Using the For…Next Loop

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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 decimals,

or include variables and mathematical expressions

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Entering the For…Next Loop Code

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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• Body executes at least once

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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

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Top-Controlled Do While Loops

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Entering a Do Loop Using IntelliSense

►In the code window, enter the intScore variable declaration and then press the ENTER key. Type Do While and a space to display the IntelliSense list. 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

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Entering a Do Loop Using IntelliSense

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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

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Bottom-Controlled Do While Loop

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Do Until Loops

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User Input Loops

►Do loops often are written to end the loop when the user enters a certain value or performs a certain action such as tapping or clicking the Cancel button in an input box

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Avoiding Infinite Loops

►An infinite loop is a loop that never ends

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Priming the Loop

►Starting a loop with a preset value in the variable(s) tested in the condition is called priming the loop

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Validating Data

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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

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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

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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 2012 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

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►With the application open in the code window, press and hold or right-click line 46, which contains the code where you want to set a breakpoint, and then point to Breakpoint on the shortcut menu

►Tap or click Insert Breakpoint on the submenu►To run and test the program with the breakpoint, tap or

click the Start Debugging button on the Standard toolbar►Tap or click the Enter Weight Loss button. Type 3.4 as

the weight loss amount of the first team member►Tap or click the OK button in the input box

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►Point to the variable decWeightLoss on line 46►You can view the value in any other variable

within execution scope by pointing to that variable. To illustrate, point to the variable decTotalWeightLoss on line 46

►Continue the program by tapping or clicking the Continue button on the Standard toolbar. Notice that the Continue button is the same as the Start Debugging button

►Point to the decTotalWeightLoss variable

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►To remove a breakpoint, press and hold or right-click the statement containing the breakpoint, and then point to Breakpoint on the shortcut menu

►Tap or click Delete Breakpoint on the Breakpoint submenu

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Publishing an Application with ClickOnce 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 2012, 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

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►With the application open, tap or click BUILD on the menu bar

►Tap or click Publish Fitness Challenge 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

►Tap or click the Next button. If necessary, tap or click the From a CD-ROM or DVD-ROM radio button

►Tap or click the Next button. If necessary, tap or click the “The application will not check for updates” radio button

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►Tap or click the Next button►Tap or click the Finish button►To view the finished result, minimize the Visual Studio

window and then open the Search charm. Type Computer in the Search box. Double-tap or double-click the USB drive icon to view the published installation folder

►To install the application, double-tap or double-click the setup file

►After installation, the program runs. To run the installed application again, open the Search charm, type Fitness, and then click the Fitness Challenge icon

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Program Design

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Program Design

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Event Planning Document

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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

6


Summary

►Repeat a process using a For…Next loop►Repeat a process using a Do loop►Avoid infinite loops►Prime a loop►Validate data

6


Summary

►Create a nested loop►Select the best type of loop►Debug using DataTips at breakpoints►Publish a finished application using ClickOnce

technology

Microsoft Visual Basic 2012

Loop Structures

CHAPTER SIX COMPLETE

Microsoft Visual Basic 2012 Loop Structures CHAPTER SIX.

Documents

file menu

loop structures9 slide

loop structures chapter

menu items

nested loop

loop structures11

fornext loop

menu names