Microsoft Visual Basic 2010 Reloaded Fourth Edition Chapter

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Microsoft Visual Basic 2010: Reloaded Fourth Edition Chapter Six Repeating Program Instructions

Microsoft Visual Basic 2010: Reloaded Fourth Edition Chapter Six Repeating Program Instructions

Objectives After studying this chapter, you should be able to: • Differentiate between a

Objectives After studying this chapter, you should be able to: • Differentiate between a pretest and a posttest loop • Include pretest and posttest loops in pseudocode and in a flowchart • Write a Do…Loop statement • Utilize counters and accumulators • Display a dialog box using the Input. Box function Microsoft Visual Basic 2010: Reloaded, Fourth Edition 2

Objectives (cont'd. ) • • Include a list box in an interface Enable and

Objectives (cont'd. ) • • Include a list box in an interface Enable and disable a control Refresh the screen Delay program execution Microsoft Visual Basic 2010: Reloaded, Fourth Edition 3

The Repetition Structure • Repetition structure (or loop): a structure that repeatedly processes one

The Repetition Structure • Repetition structure (or loop): a structure that repeatedly processes one or more program instructions until a condition is met • Looping condition: the requirement for repeating the instructions • Loop exit condition: the requirement for not repeating the instructions Microsoft Visual Basic 2010: Reloaded, Fourth Edition 4

The Repetition Structure (cont’d. ) Figure 6 -1: Example of a looping condition and

The Repetition Structure (cont’d. ) Figure 6 -1: Example of a looping condition and a loop exit condition Microsoft Visual Basic 2010: Reloaded, Fourth Edition 5

The Repetition Structure (cont’d. ) Figure 6 -2: Problem specification for the Getting to

The Repetition Structure (cont’d. ) Figure 6 -2: Problem specification for the Getting to a Million Club application Figure 6 -3: Sample run of the Getting to a Million Club application Microsoft Visual Basic 2010: Reloaded, Fourth Edition 6

The Repetition Structure (cont’d. ) Figure 6 -4: Pseudocode containing only the sequence structure

The Repetition Structure (cont’d. ) Figure 6 -4: Pseudocode containing only the sequence structure Microsoft Visual Basic 2010: Reloaded, Fourth Edition 7

The Repetition Structure (cont’d. ) • Pretest loop – The condition is evaluated before

The Repetition Structure (cont’d. ) • Pretest loop – The condition is evaluated before the instructions within the loop are processed – The instructions may be processed zero or more times • Posttest loop – The condition is evaluated after the instructions within the loop are processed – The instructions are always processed at least once Microsoft Visual Basic 2010: Reloaded, Fourth Edition 8

Figure 6 -5: Modified problem specification and pseudocode containing a loop Microsoft Visual Basic

Figure 6 -5: Modified problem specification and pseudocode containing a loop Microsoft Visual Basic 2010: Reloaded, Fourth Edition 9

The Repetition Structure (cont'd. ) • Repetition statements in Visual Basic – Do. .

The Repetition Structure (cont'd. ) • Repetition statements in Visual Basic – Do. . . Loop – For. . . Next – For Each. . . Next Microsoft Visual Basic 2010: Reloaded, Fourth Edition 10

The Do. . . Loop Statement • Do. . . Loop statement: codes both

The Do. . . Loop Statement • Do. . . Loop statement: codes both a pretest and posttest loop • Loop body: the instructions between the Do and the Loop clauses • Use While or Until to code the condition for the loop • Repetition symbol in a flowchart is the diamond Microsoft Visual Basic 2010: Reloaded, Fourth Edition 11

Figure 6 -6: How to use the Do…Loop statement Microsoft Visual Basic 2010: Reloaded,

Figure 6 -6: How to use the Do…Loop statement Microsoft Visual Basic 2010: Reloaded, Fourth Edition 12

The Do. . . Loop Statement (cont'd. ) Figure 6 -7: Flowchart for the

The Do. . . Loop Statement (cont'd. ) Figure 6 -7: Flowchart for the pretest loop example from Figure 6 -6 Microsoft Visual Basic 2010: Reloaded, Fourth Edition 13

The Do. . . Loop Statement (cont'd. ) Figure 6 -8: Flowchart for the

The Do. . . Loop Statement (cont'd. ) Figure 6 -8: Flowchart for the posttest loop example from Figure 6 -6 Microsoft Visual Basic 2010: Reloaded, Fourth Edition 14

Using Counters and Accumulators • Counter: a numeric variable used for counting • Accumulator:

Using Counters and Accumulators • Counter: a numeric variable used for counting • Accumulator: a numeric variable used for accumulating (adding together) • Initializing: assigning a beginning value to a counter or accumulator variable • Updating (or incrementing): adding a number to the value of a counter or accumulator variable • Counters are always incremented by a constant value, usually 1 Microsoft Visual Basic 2010: Reloaded, Fourth Edition 15

Figure 6 -9: Modified pseudocode and code for the calc. Button’s Click event procedure

Figure 6 -9: Modified pseudocode and code for the calc. Button’s Click event procedure Microsoft Visual Basic 2010: Reloaded, Fourth Edition 16

Using Counters and Accumulators (cont’d. ) Figure 6 -9: Modified pseudocode and code for

Using Counters and Accumulators (cont’d. ) Figure 6 -9: Modified pseudocode and code for the calc. Button’s Click event procedure (cont’d. ) Figure 6 -10: Sample run of the modified Getting to a Million Club application Microsoft Visual Basic 2010: Reloaded, Fourth Edition 17

The Sales Express Company Application • Requirements: display the average amount the company sold

The Sales Express Company Application • Requirements: display the average amount the company sold during the prior year • Input: the amount of each salesperson’s sales • Multiline property: if True, allows multiple lines of text in a text box • Read. Only property: if True, prevents a user from changing the text box contents during run time • Scroll. Bars property: specifies whether a text box has no scroll bars, horizontal or vertical, or both Microsoft Visual Basic 2010: Reloaded, Fourth Edition 18

The Sales Express Company Application (cont'd. ) Figure 6 -11: Problem specification for the

The Sales Express Company Application (cont'd. ) Figure 6 -11: Problem specification for the Sales Express Company application Microsoft Visual Basic 2010: Reloaded, Fourth Edition 19

The Sales Express Company Application (cont'd. ) Figure 6 -12: Sample run of the

The Sales Express Company Application (cont'd. ) Figure 6 -12: Sample run of the Sales Express Company application Microsoft Visual Basic 2010: Reloaded, Fourth Edition 20

The Sales Express Company Application (cont'd. ) Figure 6 -13: Pseudocode for the Average

The Sales Express Company Application (cont'd. ) Figure 6 -13: Pseudocode for the Average button’s Click event procedure Microsoft Visual Basic 2010: Reloaded, Fourth Edition 21

The Sales Express Company Application (cont'd. ) • Priming read: used to obtain the

The Sales Express Company Application (cont'd. ) • Priming read: used to obtain the first input • Update read: allows the user to update the value of an input item • Infinite (or endless) loop: a loop that has no way to end • Must verify that a variable does not contain the value 0 before using it as a divisor Microsoft Visual Basic 2010: Reloaded, Fourth Edition 22

Figure 6 -14: Flowchart for the Average button’s Click event procedure Microsoft Visual Basic

Figure 6 -14: Flowchart for the Average button’s Click event procedure Microsoft Visual Basic 2010: Reloaded, Fourth Edition 23

The Input. Box Function • Input. Box function: displays a predefined dialog box that

The Input. Box Function • Input. Box function: displays a predefined dialog box that allows the user to enter data – Contains a text message, an OK button, a Cancel button, and an input area • Input. Box function returns: – The user’s entry if the user clicks the OK button – An empty string if the user clicks the Cancel button or the Close button on the title bar Microsoft Visual Basic 2010: Reloaded, Fourth Edition 24

The Input. Box Function (cont'd. ) Figure 6 -15: Example of an input dialog

The Input. Box Function (cont'd. ) Figure 6 -15: Example of an input dialog box Microsoft Visual Basic 2010: Reloaded, Fourth Edition 25

The Input. Box Function (cont'd. ) • Input. Box function arguments: – prompt: the

The Input. Box Function (cont'd. ) • Input. Box function arguments: – prompt: the message to display inside the dialog box – title: the text to display in the dialog box’s title bar – default. Response: a prefilled value for the user input Microsoft Visual Basic 2010: Reloaded, Fourth Edition 26

Figure 6 -16: How to use the Input. Box function Microsoft Visual Basic 2010:

Figure 6 -16: How to use the Input. Box function Microsoft Visual Basic 2010: Reloaded, Fourth Edition 27

The Input. Box Function (cont'd. ) Figure 6 -16: How to use the Input.

The Input. Box Function (cont'd. ) Figure 6 -16: How to use the Input. Box function (cont'd. ) Microsoft Visual Basic 2010: Reloaded, Fourth Edition 28

Figure 6 -17: Code associated with the pseudocode and flowchart shown in Figures 6

Figure 6 -17: Code associated with the pseudocode and flowchart shown in Figures 6 -13 and 6 -14, respectively Microsoft Visual Basic 2010: Reloaded, Fourth Edition 29

The Input. Box Function (cont'd. ) Figure 6 -17: Code associated with the pseudocode

The Input. Box Function (cont'd. ) Figure 6 -17: Code associated with the pseudocode and flowchart shown in Figures 6 -13 and 6 -14, respectively (cont’d. ) Microsoft Visual Basic 2010: Reloaded, Fourth Edition 30

Including a List Box in an Interface • List box: displays a list of

Including a List Box in an Interface • List box: displays a list of choices from which the user can select zero or more choices • Selection. Mode property: controls the number of choices a user can select – None: user can scroll but not select anything – One: user can select one item – Multi. Simple and Multi. Extended: user can select multiple items Microsoft Visual Basic 2010: Reloaded, Fourth Edition 31

Adding Items to a List Box • Items collection: a collection of the items

Adding Items to a List Box • Items collection: a collection of the items in a list box • Collection: a group of one or more individual objects treated as one unit • Add method: adds an item to the list box’s Items collection – Items to be added must be converted to String – String Collection Editor window can be used to specify list items during design time • Load event of a form: occurs when an application is started and the form is displayed for the first time Microsoft Visual Basic 2010: Reloaded, Fourth Edition 32

Adding Items to a List Box (cont'd. ) Figure 6 -18: String Collection Editor

Adding Items to a List Box (cont'd. ) Figure 6 -18: String Collection Editor window Microsoft Visual Basic 2010: Reloaded, Fourth Edition 33

Adding Items to a List Box (cont'd. ) Figure 6 -19: How to use

Adding Items to a List Box (cont'd. ) Figure 6 -19: How to use the Items collection’s Add method Microsoft Visual Basic 2010: Reloaded, Fourth Edition 34

Adding Items to a List Box (cont'd. ) Figure 6 -20: Add methods entered

Adding Items to a List Box (cont'd. ) Figure 6 -20: Add methods entered in the Main. Form’s Load event procedure Microsoft Visual Basic 2010: Reloaded, Fourth Edition 35

Adding Items to a List Box (cont'd. ) Figure 6 -21: Result of processing

Adding Items to a List Box (cont'd. ) Figure 6 -21: Result of processing the Add methods in Figure 6 -20 Microsoft Visual Basic 2010: Reloaded, Fourth Edition 36

Adding Items to a List Box (cont'd. ) Figure 6 -22: Sample run of

Adding Items to a List Box (cont'd. ) Figure 6 -22: Sample run of the Jasper’s Food Hut application Figure 6 -23: Add to List button’s Click event procedure in the Jasper’s Food Hut application Microsoft Visual Basic 2010: Reloaded, Fourth Edition 37

Adding Items to a List Box (cont'd. ) Figure 6 -24: Sample run of

Adding Items to a List Box (cont'd. ) Figure 6 -24: Sample run of the Clark’s Chicken application Figure 6 -25: Add to List button’s Click event procedure in the Clark’s Chicken application Microsoft Visual Basic 2010: Reloaded, Fourth Edition 38

Adding Items to a List Box (cont'd. ) • Sorted property: – Determines if

Adding Items to a List Box (cont'd. ) • Sorted property: – Determines if the list box items are sorted – Sort order is dictionary order Figure 6 -26: Examples of the list box’s Sorted property Microsoft Visual Basic 2010: Reloaded, Fourth Edition 39

Accessing Items in a List Box • Index: – A unique number that identifies

Accessing Items in a List Box • Index: – A unique number that identifies an item in a collection – Is zero-relative: the first item has index of 0 Microsoft Visual Basic 2010: Reloaded, Fourth Edition 40

Accessing Items in a List Box (cont'd. ) Figure 6 -27: How to access

Accessing Items in a List Box (cont'd. ) Figure 6 -27: How to access an item in a list box Microsoft Visual Basic 2010: Reloaded, Fourth Edition 41

Determining the Number of Items in a List Box • Items. Count property: stores

Determining the Number of Items in a List Box • Items. Count property: stores the number of items in a list box – Count value is always one higher than the highest index in the list box Microsoft Visual Basic 2010: Reloaded, Fourth Edition 42

Figure 6 -28: How to determine the number of items in a list box

Figure 6 -28: How to determine the number of items in a list box Microsoft Visual Basic 2010: Reloaded, Fourth Edition 43

The Selected. Item and Selected. Index Properties • Selected. Item property: – Contains the

The Selected. Item and Selected. Index Properties • Selected. Item property: – Contains the value of the selected item in the list – If nothing is selected, it contains the empty string • Selected. Index property: – Contains the index of the selected item in the list – If nothing is selected, it contains the value -1 • Default list box item: the item that is selected by default when the interface first appears Microsoft Visual Basic 2010: Reloaded, Fourth Edition 44

The Selected. Item and Selected. Index Properties (cont'd. ) Figure 6 -29: Item selected

The Selected. Item and Selected. Index Properties (cont'd. ) Figure 6 -29: Item selected in the animal. List. Box Microsoft Visual Basic 2010: Reloaded, Fourth Edition 45

Figure 6 -30: How to use the Selected. Item and Selected. Index properties Microsoft

Figure 6 -30: How to use the Selected. Item and Selected. Index properties Microsoft Visual Basic 2010: Reloaded, Fourth Edition 46

The Selected. Item and Selected. Index Properties (cont'd. ) Figure 6 -31: How to

The Selected. Item and Selected. Index Properties (cont'd. ) Figure 6 -31: How to select the default list box item Microsoft Visual Basic 2010: Reloaded, Fourth Edition 47

The Selected. Value. Changed and Selected. Index. Changed Events • Selected. Value. Changed and

The Selected. Value. Changed and Selected. Index. Changed Events • Selected. Value. Changed and Selected. Index. Changed events: – Occur when a user selects an item in a list box – Occur when a code statement selects an item in a list box Microsoft Visual Basic 2010: Reloaded, Fourth Edition 48

The Selected. Value. Changed and Selected. Index. Changed Events (cont’d. ) Figure 6 -32:

The Selected. Value. Changed and Selected. Index. Changed Events (cont’d. ) Figure 6 -32: Code showing the Selected. Value. Changed and Selected. Index. Changed event procedures Microsoft Visual Basic 2010: Reloaded, Fourth Edition 49

The Selected. Value. Changed and Selected. Index. Changed Events (cont’d. ) Figure 6 -32:

The Selected. Value. Changed and Selected. Index. Changed Events (cont’d. ) Figure 6 -32: Code showing the Selected. Value. Changed and Selected. Index. Changed event procedures (cont’d. ) Microsoft Visual Basic 2010: Reloaded, Fourth Edition 50

The Selected. Value. Changed and Selected. Index. Changed Events (cont’d. ) Figure 6 -32:

The Selected. Value. Changed and Selected. Index. Changed Events (cont’d. ) Figure 6 -32: Code showing the Selected. Value. Changed and Selected. Index. Changed event procedures (cont’d. ) Microsoft Visual Basic 2010: Reloaded, Fourth Edition 51

The Selected. Value. Changed and Selected. Index. Changed Events (cont’d. ) Figure 6 -33:

The Selected. Value. Changed and Selected. Index. Changed Events (cont’d. ) Figure 6 -33: Result of processing the code shown in Figure 6 -32 Microsoft Visual Basic 2010: Reloaded, Fourth Edition 52

The Product Finder Application • • Allows the user to enter a product ID

The Product Finder Application • • Allows the user to enter a product ID Searches for the ID in a list box If found, highlights the ID If not found, ensures that no ID is highlighted in the list box Microsoft Visual Basic 2010: Reloaded, Fourth Edition 53

Figure 6 -34: Sample run of the application when the produce ID is found

Figure 6 -34: Sample run of the application when the produce ID is found Figure 6 -35: Sample run of the application when the product ID is not found Microsoft Visual Basic 2010: Reloaded, Fourth Edition 54

The Product Finder Application (cont'd. ) Figure 6 -36: Pseudocode for the Find button’s

The Product Finder Application (cont'd. ) Figure 6 -36: Pseudocode for the Find button’s Click event procedure Microsoft Visual Basic 2010: Reloaded, Fourth Edition 55

Figure 6 -37: Product Finder application’s code Microsoft Visual Basic 2010: Reloaded, Fourth Edition

Figure 6 -37: Product Finder application’s code Microsoft Visual Basic 2010: Reloaded, Fourth Edition 56

Figure 6 -37: Product Finder application’s code (cont’d. ) Microsoft Visual Basic 2010: Reloaded,

Figure 6 -37: Product Finder application’s code (cont’d. ) Microsoft Visual Basic 2010: Reloaded, Fourth Edition 57

The Color Viewer Application • Enabled property: used to enable or disable a control

The Color Viewer Application • Enabled property: used to enable or disable a control – When False, the control appears dimmed (grayed out), indicating it is not available for use • Refresh method: ensures that the computer processes any previous lines of code that affect the interface’s appearance • Sleep method: delays program execution – Argument is specified in milliseconds Microsoft Visual Basic 2010: Reloaded, Fourth Edition 58

The Color Viewer Application (cont’d. ) Figure 6 -38: Main. Form in the Color

The Color Viewer Application (cont’d. ) Figure 6 -38: Main. Form in the Color Viewer application Microsoft Visual Basic 2010: Reloaded, Fourth Edition 59

The Color Viewer Application (cont’d. ) Figure 6 -39: View Colors button’s Click event

The Color Viewer Application (cont’d. ) Figure 6 -39: View Colors button’s Click event procedure Microsoft Visual Basic 2010: Reloaded, Fourth Edition 60

Programming Tutorial 1 • Creating the Roll ‘Em Game Figure 6 -41: Main. Form

Programming Tutorial 1 • Creating the Roll ‘Em Game Figure 6 -41: Main. Form for the Roll ‘Em Game application Microsoft Visual Basic 2010: Reloaded, Fourth Edition 61

Programming Tutorial 2 • Coding the Just Birthdays Application Figure 6 -52: Main. Form

Programming Tutorial 2 • Coding the Just Birthdays Application Figure 6 -52: Main. Form for the Just Birthdays application Microsoft Visual Basic 2010: Reloaded, Fourth Edition 62

Programming Example • Grade Calculator Application Figure 6 -63: Main. Form in the Grade

Programming Example • Grade Calculator Application Figure 6 -63: Main. Form in the Grade Calculator application Microsoft Visual Basic 2010: Reloaded, Fourth Edition 63

Summary • The three programming structures are sequence, selection, and repetition • Repetition structure

Summary • The three programming structures are sequence, selection, and repetition • Repetition structure (or loop): repeatedly processes a set of instructions • Pretest loop tests the condition before the instructions are processed • Posttest loop tests the condition after the instructions are processed • Do. . . Loop statement: codes a pretest or posttest loop Microsoft Visual Basic 2010: Reloaded, Fourth Edition 64

Summary (cont'd. ) • Use a While or Until condition in a Do. .

Summary (cont'd. ) • Use a While or Until condition in a Do. . . Loop • Flowchart symbol for repetition is a diamond • Counter and accumulators: variables that calculate subtotals, and averages • Priming read gets the first value prior to the loop • Update read gets remaining values from the user • Input. Box function: allows user input • Verify that a variable does not contain a value of 0 before using it as a divisor • List box: displays a list of choices Microsoft Visual Basic 2010: Reloaded, Fourth Edition 65

Summary (cont'd. ) • List box’s Items collection: contains the items in the list

Summary (cont'd. ) • List box’s Items collection: contains the items in the list box • Use String Collection Editor window to add list items during design time • Items. Add method: adds an item to the list during run time • Form’s Load event occurs before the form appears • List box item’s index is used to access the item • Items. Count property stores the number of items Microsoft Visual Basic 2010: Reloaded, Fourth Edition 66

Summary (cont'd. ) • Selected. Item property of a list box: contains the value

Summary (cont'd. ) • Selected. Item property of a list box: contains the value of the selected item in the list • Selected. Index property of a list box: contains the index position of the selected item in the list • Selected. Value. Changed and Selected. Index. Changed events occur when an item in a list box is selected • Enabled property: enables or disables a control • Sleep method: delays program execution • Me. Refresh: refreshes (redraws) the form Microsoft Visual Basic 2010: Reloaded, Fourth Edition 67