1. Chapter 6: The Repetition Structure
Programming with Microsoft Visual Basic .NET, Second Edition

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

3. The Repetition Structure
Use the repetition structure to repeatedly process one or more program instructions until some condition is met, at which time the repetition ends
The repetition structure is referred to as a loop
Programming with Microsoft Visual Basic .NET, Second Edition

4. The Repetition Structure (continued)
Pretest loop: evaluation occurs before the instructions within the loop are processed
Posttest loop: evaluation occurs after the instructions within the loop are processed
Programming with Microsoft Visual Basic .NET, Second Edition

5. The For…Next Loop
Use the For…Next statement to code a loop that repeats for a specific number of times
Figure 6-2: Syntax and examples of the For...Next statement
Programming with Microsoft Visual Basic .NET, Second Edition

6. The For…Next Loop (continued)
Figure 6-2: Syntax and examples of the For...Next statement (continued)
Programming with Microsoft Visual Basic .NET, Second Edition

7. The For…Next Loop (continued)
counter is a numeric variable that keeps track of how many times the loop instructions are repeated
startvalue, endvalue, and stepvalue
Must be numeric
Can be positive or negative, integer or non-integer
Default stepvalue is 1
Programming with Microsoft Visual Basic .NET, Second Edition

8. The For…Next Loop (continued)
Figure 6-4: Pseudocode and flowchart for the first example shown in Figure 6-2
Programming with Microsoft Visual Basic .NET, Second Edition

9. The For…Next Loop (continued)
For…Next loop examples:
Dim count As Integer
For count = 0 to 3 Step 1
Debug.WriteLine(count)
Next count
For count = 3 to 0 Step -1
For count = 0 to 10 Step 2
Dim loc As Single
For loc = 0.5 To 15 Step 0.5
Debug.WriteLine(loc)
Next loc
Programming with Microsoft Visual Basic .NET, Second Edition

10. The Do…Loop Statement
Unlike the For…Next statement, the Do…Loop statement can be used to code both a pretest loop and a posttest loop
The Do…Loop statement begins with the Do clause and ends with the Loop clause
Programming with Microsoft Visual Basic .NET, Second Edition

11. The Do…Loop Statement (continued)
Figure 6-7: Syntax and examples of the Do...Loop statement
Programming with Microsoft Visual Basic .NET, Second Edition

12. The Do…Loop Statement (continued)
Figure 6-7: Syntax and examples of the Do...Loop statement (continued)
Programming with Microsoft Visual Basic .NET, Second Edition

13. The Do…Loop Statement (continued)
Figure 6-9: Flowcharts for the examples shown in Figure 6-7
Programming with Microsoft Visual Basic .NET, Second Edition

14. The Do…Loop Statement (continued)
Figure 6-9: Flowcharts for the examples shown in Figure 6-7 (continued)
Programming with Microsoft Visual Basic .NET, Second Edition

15. Using Counters and Accumulators
Counters and accumulators are used within a repetition structure to calculate subtotals, totals, and averages
A counter is a numeric variable used for counting something and is typically updated by 1
An accumulator is a numeric variable used for accumulating and is updated by an amount that varies
Programming with Microsoft Visual Basic .NET, Second Edition

16. Using Counters and Accumulators (continued)
Initializing: assigning a beginning value to the counter or accumulator
Updating (incrementing): adding a number to the value stored in the counter or accumulator
Programming with Microsoft Visual Basic .NET, Second Edition

17. Nested Repetition Structures Lesson B Objectives
Nest repetition structures
Programming with Microsoft Visual Basic .NET, Second Edition

18. Nesting Repetition Structures
In a nested repetition structure, one loop, referred to as the inner loop, is placed entirely within another loop, called the outer loop
A clock uses nested loops to keep track of the time
Programming with Microsoft Visual Basic .NET, Second Edition

19. Nesting Repetition Structures (continued)
Figure 6-16: Nested loops used by a clock
Programming with Microsoft Visual Basic .NET, Second Edition

20. The Grade Calculator Application
Professor Arkins needs an application that allows him to assign a grade to any number of students
Each student’s grade is based on three test scores, with each test worth 100 points
The application should total the test scores and then assign the appropriate grade, using the table shown on the next slide
Programming with Microsoft Visual Basic .NET, Second Edition

21. The Grade Calculator Application (continued)
Total points earned
Grade
270–300 A
240–269 B
210–239 C
180–209 D
below 180 F
Programming with Microsoft Visual Basic .NET, Second Edition

22. The Grade Calculator Application (continued)
uiAssignGradeButton’s Click event procedure
Allows Professor Arkins to enter each student’s test scores, and then assign the appropriate grade
Contains two loops, one nested within the other
A For...Next statement controls the inner loop
Programming with Microsoft Visual Basic .NET, Second Edition

23. The Grade Calculator Application (continued)
uiAssignGradeButton’s Click event procedure (continued)
A Do...Loop statement controls the outer loop
The inner loop is a pretest loop
The outer loop is a posttest loop
Programming with Microsoft Visual Basic .NET, Second Edition

24. The Grade Calculator Application (continued)
Figure 6-20: Sample run of the application that contains the procedure
Programming with Microsoft Visual Basic .NET, Second Edition

25. Coding the Shoppers Haven Application Lesson C Objectives
Select the existing text in a text box
Prevent a form from closing
Programming with Microsoft Visual Basic .NET, Second Edition

26. Shoppers Haven
The manager of Shoppers Haven wants an application that the store clerks can use to calculate the discounted price of an item, using discount rates from 10% through 30% in increments of 5%
The clerks will enter the item’s original price
The application should display the discount rates and the discounted prices in the interface
Programming with Microsoft Visual Basic .NET, Second Edition

27. Shoppers Haven (continued)
Figure 6-21: User interface for the Shoppers Haven application
Programming with Microsoft Visual Basic .NET, Second Edition

28. Shoppers Haven (continued)
Figure 6-22: TOE chart for the Shoppers Haven application
Programming with Microsoft Visual Basic .NET, Second Edition

29. Shoppers Haven (continued)
Figure 6-23: Pseudocode for the Calculate button’s Click event procedure
Programming with Microsoft Visual Basic .NET, Second Edition

30. Shoppers Haven (continued)
Figure 6-27: Discounted prices shown in the Shoppers Haven application
Programming with Microsoft Visual Basic .NET, Second Edition

31. Selecting the Existing Text in a Text Box
Use the SelectAll method to select all of the text contained in a text box
Syntax: textbox.SelectAll()
textbox is the name of the text box whose text you want to select
Programming with Microsoft Visual Basic .NET, Second Edition

32. Selecting the Existing Text in a Text Box (continued)
Enter the SelectAll method in a text box control’s Enter event
A text box control’s Enter event occurs when the user tabs to the control, and when the Focus method is used in code to send the focus to the control
The uiOriginalTextBox control’s Enter event is responsible for highlighting the existing text in the control
Programming with Microsoft Visual Basic .NET, Second Edition

33. Selecting the Existing Text in a Text Box (continued)
Figure 6-29: Text selected in the Shoppers Haven application
Programming with Microsoft Visual Basic .NET, Second Edition

34. Coding the TextChanged Event Procedure
A control’s TextChanged event occurs when the contents of a control’s Text property change
Use the uiOriginalTextBox’s TextChanged event to clear the contents of the uiDiscPricesLabel when the user changes the original price
Programming with Microsoft Visual Basic .NET, Second Edition

35. Coding the ShoppersForm’s Closing Event Procedure
A form’s Closing event occurs when a form is about to be closed
In the Shoppers Haven application, the Closing event procedure is responsible for:
Verifying that the user wants to exit the application
Taking an action based on the user’s response
Programming with Microsoft Visual Basic .NET, Second Edition

36. Coding the ShoppersForm’s Closing Event Procedure (continued)
Figure 6-31: Pseudocode for the ShoppersForm’s Closing event procedure
Programming with Microsoft Visual Basic .NET, Second Edition

37. Coding the ShoppersForm’s Closing Event Procedure (continued)
Figure 6-33: Message box displayed by the form’s Closing event
Programming with Microsoft Visual Basic .NET, Second Edition

38. Summary
Repetition structure (loop): the computer repeats a set of instructions until some condition is met
Code a repetition structure in Visual Basic .NET using one of the following statements: For...Next, Do...Loop, and For Each…Next
The For...Next statement is pretest loops only
The Do...Loop statement can code pretest and posttest loops
Programming with Microsoft Visual Basic .NET, Second Edition

39. Summary (continued) To use a counter or accumulator:
Initialize, if necessary
Update using an assignment statement in a repetition structure
To nest a repetition structure, place the entire inner loop within the outer loop
Programming with Microsoft Visual Basic .NET, Second Edition

40. Summary (continued)
To process code when the user tabs to a control, or when the Focus method is used in code to send the focus to the control, enter the code in the control’s Enter event procedure
To process code when a form is about to be closed, enter the code in the form’s Closing event procedure
Programming with Microsoft Visual Basic .NET, Second Edition