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Microsoft Visual Basic 2008: Reloaded Third Edition

Microsoft Visual Basic 2008: Reloaded Third Edition. Chapter Six The Do Loop and List Boxes. Objectives. After studying this chapter, you should be able to: Include the Do loop in both pseudocode and a flowchart Write a Do…Loop statement Initialize counters and accumulators

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Microsoft Visual Basic 2008: Reloaded Third Edition

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  1. Microsoft Visual Basic 2008: ReloadedThird Edition Chapter Six The Do Loop and List Boxes

  2. Objectives After studying this chapter, you should be able to: • Include the Do loop in both pseudocode and a flowchart • Write a Do…Loop statement • Initialize counters and accumulators • Display a dialog box using the InputBox function • Refresh the screen Microsoft Visual Basic 2008: Reloaded, Third Edition

  3. Objectives (continued) • Delay program execution • Enable and disable a control Microsoft Visual Basic 2008: Reloaded, Third Edition

  4. The Repetition Structure • Repetition structure (or loop): a structure that repeatedly processes one or more program instructions until a condition is met • 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 2008: Reloaded, Third Edition

  5. The Repetition Structure (continued) • Repetition statements in Visual Basic • Do...Loop • For...Next • For Each...Next Microsoft Visual Basic 2008: Reloaded, Third Edition

  6. The Do...Loop Statement • Do...Loop statement: codes both a pretest or posttest loop • Use While or Until to code the condition for the loop • Repetition symbol in a flowchart is the diamond Microsoft Visual Basic 2008: Reloaded, Third Edition

  7. The Do...Loop Statement (continued) Figure 6-1: How to use the Do…Loop statement Microsoft Visual Basic 2008: Reloaded, Third Edition

  8. The Do...Loop Statement (continued) Figure 6-1: How to use the Do…Loop statement (continued) Microsoft Visual Basic 2008: Reloaded, Third Edition

  9. The Do...Loop Statement (continued) Figure 6-2: Processing steps for the pretest loop example Microsoft Visual Basic 2008: Reloaded, Third Edition

  10. The Do...Loop Statement (continued) Figure 6-3: Processing steps for the posttest loop example Microsoft Visual Basic 2008: Reloaded, Third Edition

  11. The Do...Loop Statement (continued) Figure 6-4: Pseudocode and flowchart for the pretest loop example Microsoft Visual Basic 2008: Reloaded, Third Edition

  12. The Do...Loop Statement (continued) Figure 6-5: Pseudocode and flowchart for the posttest loop example Microsoft Visual Basic 2008: Reloaded, Third Edition

  13. The Do...Loop Statement (continued) Figure 6-6: Examples showing that the pretest and posttest loops do not always produce the same results Microsoft Visual Basic 2008: Reloaded, Third Edition

  14. 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 2008: Reloaded, Third Edition

  15. The InputBox Function • Function: a predefined procedure that performs a specific task and returns a value • InputBox 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 • InputBox 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 2008: Reloaded, Third Edition

  16. The InputBox Function (continued) Figure 6-7: Example of a dialog box created by the InputBox function Microsoft Visual Basic 2008: Reloaded, Third Edition

  17. The InputBox Function (continued) • InputBox function parameters: • prompt: the message to display inside the dialog box • title: the text to display in the dialog box’s title bar • defaultResponse: a prefilled value for the user input Microsoft Visual Basic 2008: Reloaded, Third Edition

  18. The InputBox Function (continued) Figure 6-8: How to use the InputBox function Microsoft Visual Basic 2008: Reloaded, Third Edition

  19. The InputBox Function (continued) Figure 6-8: How to use the InputBox function (continued) Microsoft Visual Basic 2008: Reloaded, Third Edition

  20. The Sales Express Application • Requirements: display the average amount the company sold during the prior year • Input: the amount of each salesperson’s sales • Priming read: used to obtain the first input • Must verify that a variable does not contain the value 0 before using it as a divisor Microsoft Visual Basic 2008: Reloaded, Third Edition

  21. The Sales Express Application (continued) Figure 6-9: Pseudocode for the Sales Express application Microsoft Visual Basic 2008: Reloaded, Third Edition

  22. The Sales Express Application (continued) Figure 6-10: Sales Entry dialog box Figure 6-11: Average sales amount displayed in the interface Microsoft Visual Basic 2008: Reloaded, Third Edition

  23. Figure 6-2: Code for the calcButton in the Sales Express application Microsoft Visual Basic 2008: Reloaded, Third Edition

  24. Using a List Box in an Interface • List box: displays a list of choices from which the user can select zero or more choices • SelectionModeproperty: controls the number of choices a user can select • None: user can scroll but not select anything • One: user can select one item • MultiSimple and MultiExtended: user can select multiple items Microsoft Visual Basic 2008: Reloaded, Third Edition

  25. 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 • Load event of a form: occurs when an application is started and the form is displayed for the first time Microsoft Visual Basic 2008: Reloaded, Third Edition

  26. Adding Items to a List Box (continued) Figure 6-13: How to add items to a list box Microsoft Visual Basic 2008: Reloaded, Third Edition

  27. Adding Items to a List Box (continued) Figure 6-14: Add methods entered in the form’s Load event procedure Microsoft Visual Basic 2008: Reloaded, Third Edition

  28. Adding Items to a List Box (continued) • Sorted property: • Determines if the list box items are sorted • Sort order is dictionary order Figure 6-15: Items added to the animalListBox and codeListBox Microsoft Visual Basic 2008: Reloaded, Third Edition

  29. 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 2008: Reloaded, Third Edition

  30. Accessing Items in a List Box (continued) Figure 6-16: How to access an item in a list box Microsoft Visual Basic 2008: Reloaded, Third Edition

  31. 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 2008: Reloaded, Third Edition

  32. Figure 6-17: How to determine the number of items in a list box Microsoft Visual Basic 2008: Reloaded, Third Edition

  33. The SelectedItem and SelectedIndex Properties • SelectedItem property: • Contains the value of the selected item in the list • If nothing is selected, it contains the empty string • SelectedIndex 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 2008: Reloaded, Third Edition

  34. The SelectedItem and SelectedIndex Properties (continued) Figure 6-18: Item selected in the animalListBox Microsoft Visual Basic 2008: Reloaded, Third Edition

  35. Figure 6-19: How to use the SelectedItem and SelectedIndex properties Microsoft Visual Basic 2008: Reloaded, Third Edition

  36. The SelectedItem and SelectedIndex Properties (continued) Figure 6-20: How to select the default list box item Microsoft Visual Basic 2008: Reloaded, Third Edition

  37. The SelectedItem and SelectedIndex Properties (continued) Figure 6-21: Code to select the default item in each list box Microsoft Visual Basic 2008: Reloaded, Third Edition

  38. The SelectedValueChanged and SelectedIndexChanged Events • SelectedValueChanged and SelectedIndexChanged 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 2008: Reloaded, Third Edition

  39. The SelectedValueChanged and SelectedIndexChanged Events (continued) Figure 6-22: SelectedValueChanged and SelectedIndexChanged event procedures Microsoft Visual Basic 2008: Reloaded, Third Edition

  40. The SelectedValueChanged and SelectedIndexChanged Events (continued) Figure 6-23: Result of processing the SelectedValueChanged and SelectedIndexChanged event procedures Microsoft Visual Basic 2008: Reloaded, Third Edition

  41. 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 Microsoft Visual Basic 2008: Reloaded, Third Edition

  42. The Product Finder Application (continued) Figure 6-24: Pseudocode for the Product Finder application Microsoft Visual Basic 2008: Reloaded, Third Edition

  43. The Product Finder Application (continued) Figure 6-25: Sample run of the application when an ID is found Figure 6-26: Sample run of the application when an ID is not found Microsoft Visual Basic 2008: Reloaded, Third Edition

  44. Figure 6-27: Code for the form’s Load event and findButton’s Click event procedures Microsoft Visual Basic 2008: Reloaded, Third Edition

  45. Programming Tutorial • Creating the Roll ‘Em Game • Sleep method: delays execution of the program • Refresh method: redraws the user interface Figure 6-29: User interface Microsoft Visual Basic 2008: Reloaded, Third Edition

  46. Programming Example • Grade Calculator Figure 6-43: User interface Microsoft Visual Basic 2008: Reloaded, Third Edition

  47. 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 Microsoft Visual Basic 2008: Reloaded, Third Edition

  48. Summary (continued) • Do...Loop statement: codes a pretest or posttest loop • Use a While or Until condition in a Do...Loop • Flowchart symbol for repetition is a diamond • Counter and accumulators: variables that calculate subtotals, totals, and averages • InputBox function: allows user input • Verify that a variable does not contain a value of 0 before using it as a divisor Microsoft Visual Basic 2008: Reloaded, Third Edition

  49. Summary (continued) • List box: contains a minimum of three selections • List box’s Items collection: contains the items in the list box • Items.Add method: adds an item to the list • 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 • SelectedItem property of a list box: contains the value of the selected item in the list Microsoft Visual Basic 2008: Reloaded, Third Edition

  50. Summary (continued) • SelectedIndex property of a list box: contains the index position of the selected item in the list • SelectedValueChanged and SelectedIndexChanged events occur when an item in a list box is selected • Sleep method: delays program execution • Me.Refresh: refreshes (redraws) the form • Enabled property: used to enable or disable a control Microsoft Visual Basic 2008: Reloaded, Third Edition

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