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
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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
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4. The Repetition Structure (continued)
Repetition statements in Visual Basic
For...Next
Do...Loop
For Each...Next
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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
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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
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7. The For...Next Statement (continued)
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8. The For...Next Statement (continued)
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9. The 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
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10. The Financial.Pmt Method (continued)
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11. The Monthly Payment Calculator Application
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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
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13. Coding a Control’s TextChanged Event Procedure
Occurs when a change is made in a control’s Text property
Change may be made by user or the program
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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
SelectionMode property: 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
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15. Using a List Box in an Interface (continued)
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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
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17. Adding Items to a List Box (continued)
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18. Adding Items to a List Box (continued)
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19. Adding Items to a List Box (continued)
Sorted property:
Determines if the list box items are sorted
Sort order is dictionary order
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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
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21. The SelectedValueChanged and SelectedIndexChanged Events
SelectedValueChanged and SelectedIndexChanged events: occur when a user selects an item in a list box
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22. The SelectedValueChanged and SelectedIndexChanged Events (continued)
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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
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24. Using a Combo Box in an Interface (continued)
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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)
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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
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27. The Do...Loop Statement (continued)
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28. The Do...Loop Statement (continued)
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29. The Do...Loop Statement (continued)
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30. The Do...Loop Statement (continued)
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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
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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])
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33. The InputBox Function (continued)
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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
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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
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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
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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
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