1. Tutorial 10 – Class Average Application Introducing the Do…Loop While and Do…Loop Until Repetition Statements
Outline Test-Driving the Class Average Application Do…Loop While Repetition Statement Do…Loop Until Repetition Statement Creating the Class Average Application Wrap-Up

2. In this tutorial, you will learn to:
Objectives
In this tutorial, you will learn to:
Use the Do…Loop While statement.
Use the Do…Loop Until statement.
Understand counter-controlled repetition.
Transfer the focus to a control.
Enable and disable Buttons.

3. 10.1 Test-Driving the Class Average Application

4. 10.1 Test-Driving the Class Average Application
Figure 10.1　Class Average application’s Form in run mode.
Output Label
The Class Average application
Output Label displays quiz average to user

5. 10.1 Test-Driving the Class Average Application
Figure 10.2　Entering grades in the Class Average application.
Entering quiz grades
Enter a grade into the Enter grade: TextBox
Click Add Grade Button
Grade added to ListBox
Focus given to TextBox

6. 10.1 Test-Driving the Class Average Application
Figure 10.3　 Class Average application after 10 grades have been input.
Disabled Add Grade Button
Ten quiz grades entered
Entering ten grades
Add Grade Button disabled
Click Average Button to calculate average quiz grade

7. 10.1 Test-Driving the Class Average Application
Figure 10.4　Displaying the class average.
Label displaying average
Click to calculate class average
Calculating the average
Click the Average Button
Average displayed in output Label
Add Grade Button enabled

8. 10.1 Test-Driving the Class Average Application
Figure 10.5　Entering a new set of grades.
Entering another set of grades
Old quiz grades removed from ListBox
New grade added to ListBox

9. 10.2 Do…Loop While Repetition Statement
Do…Loop While example:
Dim intCouner As Integer = 1
Do 1stDisplay.Items.Add(intCounter) intCounter += 1 Loop While intCounter <= 3
Set counter to 1
Excecute body of Do…Loop While statement while the counter is less than or equal to 3

10. 10.2 Do…Loop While Repetition Statement
Figure 10.6　Do…Loop While repetition statement UML activity diagram.
Corresponding VB .NET Statements:
lstDisplay.Items.Add(intCounter)
action state
intCounter += 1
[intCounter <= 3]
decision
loop-
[intCounter
> 3]
continuation
condition
Do…Loop While repetition statement
Body of the loop executes first
Loop-continuation condition checked
If False, loop exits
If True, loop executes again

11. 10.3 Do…Loop Until Repetition Statement
Do…Loop Until example:
Dim intCouner As Integer = 1
Do 1stDisplay.Items.Add(intCounter) intCounter += 1 Loop Until intCounter > 3
Set counter to 1
Execute body of Do…Loop Until statement until the counter is greater than to 3

12. 10.3 Do…Loop Until Repetition Statement
Figure 10.7　Do…Loop Until repetition statement UML activity diagram.
Corresponding VB .NET Statements:
lstDisplay.Items.Add(intCounter)
action state
intCounter += 1
[intCounter <= 3]
Decision
[intCounter
> 3]
Do…Loop Until repetition statement
Body of the loop executes
Loop-continuation condition checked
If False, loop executes again
If True, loop exits

13. 10.4 Creating the Class Average Application

14. 10.4 Creating the Class Average Application

15. 10.4 Creating the Class Average Application
Figure 10.9　Class Average application’s Form in design view.
Template application
Contains:
ListBox
Buttons
Output Label

16. 10.4 Creating the Class Average Application
Figure 10.10　Clearing the ListBox and output Label after a calculation.
Clearing the grade
list and class average
Clearing ListBox and output Label
If output Label contains text
Clear output Label of previous result
Clear ListBox of previous quiz grades

17. 10.4 Creating the Class Average Application
Figure 10.11　Adding the grade input to the ListBox and clearing the Enter grade: TextBox.
Adding a numeric grade
to the ListBox and
clearing the user input
from the TextBox
Displaying grades
Add grade to ListBox
Clear TextBox txtInput

18. 10.4 Creating the Class Average Application
Figure 10.12　Transferring the focus to the TextBox control.
Transferring the focus
of the application to
the TextBox
Transferring focus to a control
Makes application easier to use
Use method Focus of that control

19. 10.4 Creating the Class Average Application
Accepting ten grades
Use method lstGrades.Items.Count to determine if ten grades entered
If ten grades entered:
Disable Add Grade Button
Give focus to Average Button

20. 10.4 Creating the Class Average Application
Figure 10.13　Application accepts only 10 grades.
Disabling the Add
grade Button
and transferring
the focus to the
Average Button

21. 10.4 Creating the Class Average Application
Initializing event handler variables
intTotal stores sum of all quiz grades
intGradeCounter stores number of grades entered
intGrade stores current grade entered
dblAverage stores average of quiz grades

22. 10.4 Creating the Class Average Application
Figure 10.14　Initialization phase of class-average calculation.
Initializing
variables

23. 10.4 Creating the Class Average Application
Figure 10.15　Do…Loop Until summing grades.
Using the Do…Loop
Until repetition
statement to sum
grades in the ListBox.

24. 10.4 Creating the Class Average Application
Adding quiz grades
Use a Do…Loop Until statement to retrieve ten grades
Use lstGrades.Items.Item() to retrieve grade from ListBox
Add grade to intTotal
Increment counter

25. 10.4 Creating the Class Average Application
Displaying average
Calculate average of ten quiz grades
Format and display average
Enable Add Grade Button
Transfer the focus to txtInput TextBox

26. 10.4 Creating the Class Average Application
Figure 10.16　Displaying the result of the average calculation.
Calculating the class average, enabling the Add Grade Button, and transferring the focus to the Enter Grade: TextBox.

27. ClassAverage.vb (1 of 3)
Disabling the Add Grade Button and transferring the focus to the Average Button

28. ClassAverage.vb (2 of 3)
Using a Do…Loop Until statement to calculate the class average

29. Enabling the Add Grade Button and transferring the focus to the Enter grade: TextBox
ClassAverage.vb (3 of 3)