1. Chapter 6: The Repetition Structure
Programming with Microsoft Visual Basic 2005, Third Edition

2. The Repetition Structure (Looping) Lesson A Objectives
Code the repetition structure using the For...Next and Do...Loop statements
Include the repetition structure in pseudocode
Include the repetition structure in a flowchart
Initialize and update counters and accumulators
Programming with Microsoft Visual Basic 2005, Third Edition

3. Previewing the Completed Application
Go to Run command on Windows Start menu
Browse to the VB2005\Chap06 folder
Open the Shoppers.exe file
The Shoppers Haven user interface appears
Programming with Microsoft Visual Basic 2005, Third Edition

4. Previewing the Completed Application (continued)
Figure 6-1: Interface showing the discount and discounted price amounts
Programming with Microsoft Visual Basic 2005, Third Edition

5. The Repetition Structure
Repetition structure (loop)
Repeatedly processes instructions until condition met
Example: calculate net pay for each employee
Pretest loop
Condition evaluated prior to instruction processing
Posttest loop
Condition evaluated after instruction processing
Programming with Microsoft Visual Basic 2005, Third Edition

6. The For…Next Statement
Processes instructions a specific number of times
Condition tested before processing (pretest loop)
Also called a counter controlled loop
Syntax and examples to follow
Programming with Microsoft Visual Basic 2005, Third Edition

7. The For…Next Statement (continued)
Figure 6-2: Syntax and examples of the For...Next statement (continued) Page 485
Programming with Microsoft Visual Basic 2005, Third Edition

8. The For…Next Statement (continued)
Figure 6-2: Syntax and examples of the For...Next statement
Programming with Microsoft Visual Basic 2005, Third Edition

9. The For…Next Statement (continued)
Syntactic Elements of For…Next statement
Begins with the For clause, ends with Next clause
counter: numeric variable tracking iterations
startvalue and endvalue provide looping range
stepvalue increments or decrements counter
statements: processed in the body of the loop
Hexagon: flowchart symbol representing For…Next
Programming with Microsoft Visual Basic 2005, Third Edition

10. The For…Next Statement (continued)
Figure 6-5: Page 488, Pseudocode for the first example shown in Figure 6-2
Programming with Microsoft Visual Basic 2005, Third Edition

11. The For…Next Statement (continued)
Figure 6-6: Page 489: Flowchart for the first example shown in Figure 6-2
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12. The Monthly Payment Calculator Application
Task of xCalcButton’s Click event procedure
Calculate and display monthly car payments
Use term of five years and rates from 5 – 10%
Basic structure of the For…Next statement
Use a procedure level variable, rate, as a counter
Set starting and ending values to 0.05 and 0.01
Set the step value to 0.1
Calculate monthly payment for current rate
Display interest rate and corresponding payment
Programming with Microsoft Visual Basic 2005, Third Edition

13. The Monthly Payment Calculator Application (continued)
Figure 6-8: Page 491: Sample run of the application that contains the procedure
Programming with Microsoft Visual Basic 2005, Third Edition

14. The Do…Loop Statement Do…Loop statement Syntax and examples to follow
Codes both a pretest loop and a posttest loop
Syntax and examples to follow
Observe two variations of the syntax
Variations correspond to pretest and posttest loop
Programming with Microsoft Visual Basic 2005, Third Edition

15. The Do…Loop Statement (continued)
Figure 6-9: Page 493: Syntax and examples of the Do...Loop statement (continued)
Programming with Microsoft Visual Basic 2005, Third Edition

16. The Do…Loop Statement (continued)
Figure 6-9: Syntax and examples of the Do...Loop statement
Programming with Microsoft Visual Basic 2005, Third Edition

17. The Do…Loop Statement (continued)
Syntactic elements for the Do…Loop statement
Begins with Do clause, ends with the Loop clause
Enter instructions to repeat between both clauses
Use either While or Until keyword before condition
Condition must evaluate to Boolean True or False
Location of {While|Until} condition by syntax version
Pretest loop: appears in the Do clause
Posttest loop: appears in the Loop clause
Diamond: represents loop condition in a flowchart
Programming with Microsoft Visual Basic 2005, Third Edition

18. The Do…Loop Statement (continued)
Figure 6-13: Page 495: Pseudocode and flowchart for the posttest loop example shown in Figure 6-9 (continued)
Programming with Microsoft Visual Basic 2005, Third Edition

19. The Do…Loop Statement (continued)
Figure 6-13: Pseudocode and flowchart for the posttest loop example shown in Figure 6-9
Programming with Microsoft Visual Basic 2005, Third Edition

20. Using Counters and Accumulators
Used to calculate subtotals, totals, and averages
Counter: numeric variable used for counting
Accumulator: variable used to tally various amounts
Initialize: set initial value of counter or accumulator
Updating (incrementing or decrementing)
Changing value stored in counter or accumulator
Update statement is used within a repetition structure
Programming with Microsoft Visual Basic 2005, Third Edition

21. The Sales Express Application
Objective: display average sales of company
Structure of xCalcButton Click event procedure
Use a pretest loop to retrieve each sales amount
Update accumulator within loop to tally gross sales
Update counter within loop to keep track of entries
Exit loop after data entry has been completed
If counter is > 0, calculate average sales amount
Display the average sales amount
Programming with Microsoft Visual Basic 2005, Third Edition

22. The Sales Express Application (continued)
Figure 6-15: Page 500: Pseudocode for the xCalcButton’s Click event procedure
Programming with Microsoft Visual Basic 2005, Third Edition

23. Summary – Lesson A
Repetition structure (loop): repeats a set of instructions until some condition is met
Use a For...Next statement to code pretest loops
Use a Do...Loop statement to code pretest and posttest loops
Counters and accumulators must be initialized
Counters and accumulators are updated in a loop
Programming with Microsoft Visual Basic 2005, Third Edition

24. Nested Repetition Structures Lesson B Objectives
Nest repetition structures
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25. Nesting Repetition Structures
Nested repetition structure
Inner loop placed entirely within outer loop
Placement of inner loop is known as nesting
Clocks use nested loops to keep track of the time
Analogizing minute and second hands to loops
Outer loop corresponds to the minute hands
Inner loop corresponds to the second hand
Programming with Microsoft Visual Basic 2005, Third Edition

26. Nesting Repetition Structures (continued)
Figure 6-22: Nested loops used by a clock
Programming with Microsoft Visual Basic 2005, Third Edition

27. Monthly Payment Calculator Application— Nested For...Next Statements
Objective: calculate and display car payments
Use nested loops in xCalcButton’s Click event
Role of the outer For…Next statement
Control interest rates ranging from %
Increment rates at each iteration by 1%
Role of the inner For…Next statement
Controls terms from years
Programming with Microsoft Visual Basic 2005, Third Edition

28. Figure 6-24: Monthly payments shown in the interface
Monthly Payment Calculator Application— Nested For...Next Statements (continued)
Figure 6-24: Monthly payments shown in the interface
Programming with Microsoft Visual Basic 2005, Third Edition

29. Summary – Lesson B
To nest a repetition structure, place the entire inner loop within the outer loop
Programming with Microsoft Visual Basic 2005, Third Edition

30. Coding the Shoppers Haven Application Lesson C Objectives
Include a list box in an interface
Select a list box item from code
Determine the selected item in a list box
Programming with Microsoft Visual Basic 2005, Third Edition

31. Shoppers Haven Objective: allow entry of price and discount rate
Application requirements
Discount rate range: 10% through 30%
Discount rate should be incremented by 5%
Calculate discount amount and discounted price
Display discount amount and discounted price
Programming with Microsoft Visual Basic 2005, Third Edition

32. Shoppers Haven (continued)
Figure 6-25: TOE chart for the Shoppers Haven application
Programming with Microsoft Visual Basic 2005, Third Edition

33. Shoppers Haven (continued)
Figure 6-26: Partially completed user interface for the Shoppers Haven application
Programming with Microsoft Visual Basic 2005, Third Edition

34. Including a List Box in an Interface
Displays a list of choices
User can select 0 or more items
SelectionMode property
Controls number of choices that can be selected
Values: None, One, MultiSimple, or MultiExtended
ListBox tool: used to add a list box to an interface
List box can be made any size you want
Programming with Microsoft Visual Basic 2005, Third Edition

35. Adding Items to a List Box
Collection: group of objects treated as one unit
Items collection
Refers to group of items in a list box
An index identifies each item in a collection
Items collection’s Add method:
Specifies items you want displayed in a list box
Implemented in form’s Load event procedure
Sorted property of a list box
Displays list box items in dictionary order when true
Programming with Microsoft Visual Basic 2005, Third Edition

36. Adding Items to a List Box (continued)
Figure 6-28: Syntax and examples of the Add method
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37. Adding Items to a List Box (continued)
Figure 6-29: Items added to the list boxes
Programming with Microsoft Visual Basic 2005, Third Edition

38. The SelectedItem And SelectedIndex Properties
SelectedItem property
Contains value of item selected in a list box
Value when no item is selected is the empty string
SelectedIndex property
Contains index of item selected in a list box
Value when no item is selected is the number -1
Default list box item
Appears when the application is first loaded
Can be chosen with SelectedItem and SelectedIndex
Programming with Microsoft Visual Basic 2005, Third Edition

39. The SelectedItem And SelectedIndex Properties (continued)
Figure 6-34: Completed MainForm’s Load event procedure
Programming with Microsoft Visual Basic 2005, Third Edition

40. The SelectedItem And SelectedIndex Properties (continued)
Figure 6-35: First item selected in the xRateListBox
Programming with Microsoft Visual Basic 2005, Third Edition

41. Coding the Text Box’s TextChanged Event Procedure
Control’s TextChanged event
Occurs when contents of Text property change
Additional requirement
Clear controls when TextChanged event occurs in xOrigPriceTextBox
Programming with Microsoft Visual Basic 2005, Third Edition

42. Coding the Text Box’s TextChanged Event Procedure (continued)
Figure 6-36: Completed ClearLabels procedure
Programming with Microsoft Visual Basic 2005, Third Edition

43. Coding the xCalcButton’s Click Event Procedure
Last procedure to code in application
Programming with Microsoft Visual Basic 2005, Third Edition

44. Coding the xCalcButton’s Click Event Procedure (continued)
Figure 6-37: Pseudocode for the xCalcButton’s Click event procedure
Programming with Microsoft Visual Basic 2005, Third Edition

45. Coding the xCalcButton’s Click Event Procedure (continued)
Figure 6-39: Discount and discounted price amounts shown in the interface
Programming with Microsoft Visual Basic 2005, Third Edition

46. Summary – Lesson C A list box displays a list of items
Use list box’s SelectionMode property to set number of items to select in a list box
List box items can be sorted in dictionary order
Use Item collection’s Add method to specify items that will display in the list box
Text box’s TextChanged event occurs when a change is made to the control’s contents
Programming with Microsoft Visual Basic 2005, Third Edition