Repeating Program Instructions

1. Repeating Program Instructions

2. Objectives • Include the repetition structure in pseudocode and in a flowchart • Write a For...Next statement • Calculate a periodic payment using the Financial.Pmt method • Include a list box and a combo box in an interface • Write a Do...Loop statement • Initialize and update counters and accumulators • Display a dialog box using the InputBox function • Create a multiline text box that cannot be edited • Animate a control by moving it across a form • Have the computer sound a beep VB 2005

3. 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 0 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 VB 2005

4. The Repetition Structure (continued) • Repetition statements in Visual Basic • For...Next • Do...Loop • For Each...Next VB 2005

5. The For...Next Statement • For...Next statement • Processes a set of instructions a known number of times • Is a pretest loop • Syntax: For counter [As datatype]=startvalue to endvalue [stepvalue] [statements] Next counter VB 2005

6. The For...Next Statement (continued) • Startvalue, endvalue, and stepvalue items • Control the number of times the loop is processed • Must evaluate to numeric values • Can be positive or negative • A negative stepvalue causes the loop counter to count down • Flowchart symbol for the For...Next loop is a hexagon VB 2005

7. The For...Next Statement (continued) VB 2005

8. The For...Next Statement (continued) VB 2005

9. The Financial.Pmt Method • Financial.Pmt method • Syntax: Financial.Pmt(Rate, NPer, PV[,Fv, Due]) • Calculates a periodic payment on a loan or investment • Returns the periodic payment as a Double type value • Rate and number of periods arguments must be expressed in the same units (monthly, annual, etc.) • Also calculates the amount that must be saved each period to accumulate a specific sum VB 2005

10. The Financial.Pmt Method (continued) VB 2005

11. The Monthly Payment Calculator Application VB 2005

12. Selecting the Existing Text in a Text Box • Windows standard: highlight the existing text when a text box receives the focus • SelectAll method: selects all text in a text box Syntax: textbok.selectAll() • Enter event: occurs when the text box receives the focus VB 2005

13. Coding a Control’s TextChanged Event Procedure • TextChanged event • Occurs when a change is made in a control’s Text property • Change may be made by user or the program VB 2005

14. Using a List Box in an Interface • ListBox tool: creates a ListBox control • ListBox control: displays a list of choices from which the user can select 0 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 VB 2005

15. Using a List Box in an Interface (continued) VB 2005

16. 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 • Index: • A unique number that identifies an item in a collection • Is zero-relative: the first item has index of 0 • Add method: adds an item to the list box’s Items collection VB 2005

17. Adding Items to a List Box (continued) VB 2005

18. Adding Items to a List Box (continued) VB 2005

19. Adding Items to a List Box (continued) • Sorted property: • Determines if the list box items are sorted • Sort order is dictionary order VB 2005

20. 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 VB 2005

21. The SelectedValueChanged and SelectedIndexChanged Events • SelectedValueChanged and SelectedIndexChanged events: occur when a user selects an item in a list box VB 2005

22. The SelectedValueChanged and SelectedIndexChanged Events (continued) VB 2005

23. Using a Combo Box in an Interface • ComboBox tool: creates a combo box control • ComboBox control: • Similar to a list box • May contain a text field that allows the user to type an entry that is not on the list • List portion may be hidden • Three styles of combo boxes: • Simple • DropDown • DropDownList VB 2005

24. Using a Combo Box in an Interface (continued) VB 2005

25. Using a Combo Box in an Interface (continued) • SelectedItem property: contains the value of the selected item in the list • Text property: contains the value that appears in the text portion of the control (item selected or typed in) VB 2005

26. The Do...Loop Statement • Do...Loop statement: codes both a pretest or a posttest loop • Use While or Until to code the condition for the loop • Repetition symbol in a flowchart is the diamond • Syntax: Do While condition Do Statement(s) Statement(S) Loop Loop Until condition VB 2005

27. The Do...Loop Statement (continued) VB 2005

28. The Do...Loop Statement (continued) VB 2005

29. The Do...Loop Statement (continued) VB 2005

30. The Do...Loop Statement (continued) VB 2005

31. Using Counters and Accumulators • Counter: a numeric variable used for counting • Accumulator: a numeric variable used for accumulating • Initializing: assigning a beginning value to a variable • Updating (or incrementing): adding a number to the value of a variable • Counters are always incremented by a constant value, usually 1 VB 2005

32. The InputBox Function • InputBox function: displays a predefined dialog box • Contains a text message, an OK button, a Cancel button, and an input area • Function: a predefined procedure that performs a specific task and returns a value • 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 • Syntax: InputBox(Prompt [,title], [Defaultresponse]) VB 2005

33. The InputBox Function (continued) VB 2005

34. Summary • 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 • For...Next statement: a pretest loop that will process the instructions a fixed number of times • Financial.Pmt method: calculates a periodic payment on a loan or investment VB 2005

35. Summary (continued) • SelectAll method: highlights text in a text box • TextChanged Event: occurs when a control’s text changes • List box’s Items collection: adds an item to the list • SelectedItem property of a list box: contains the value of the selected item in the list • SelectedIndex property of a list box: contains the index position of the selected item in the list VB 2005

36. Summary (continued) • Combo box: similar to a list box but may not expose the list items until clicked • Three styles of combo boxes: Simple, DropDown, and DropDownList • 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 VB 2005

37. Summary (continued) • Counter and accumulators: variables that calculate subtotals, totals, and averages • InputBox function: allows user input • Console.Beep method: plays the sound of a beep through the computer’s console speakers VB 2005