1. CSCI 3327 Visual Basic Chapter 4: Control Statements in Visual Basic (Part 2)
UTPA – Fall 2011
Part of the slides is from Dr. John Abraham’s previous lecture slides. – Xiang Lian

2. Objectives In this chapter, you will: Learn more control structures
Repetition statements
For … Next, Do … Loop While, Do … Loop Until
Selection
Select … Case
Know how to use Exit and Continue statements to break or terminate the current iteration
Learn how to use logical operators

3. In the Last Class: Repetition Structure
Visual Basic provides 7 repetition statements
Do While … Loop
While … End While
Do Until … Loop
Do … Loop While
Do … Loop Until
For … Next
For Each … Next

4. Example of For … Next Repetition Statement
Output even numbers between 2 and 10
For counter As Integer = 2 To 10 Step 2
outputLabel.Text &= counter & " "
Next

5. Discussions on For … Next Repetition Statement
For counter As Integer = 2 To 10 Step 2 … Next
Keywords: For, To, Step, Next
"counter As Integer" declares a counter of integer data type
counter – control variable name
Integer – control variable type
Initial value of control variable – 2
Final value of control variable – 10

6. Discussions on For … Next Repetition Statement (cont'd)
For counter As Integer = 2 To 10 Step 2 … Next
Increment of control variable – Step 2
If "Step 2" is missing, the default value is 1
Output all integers from 2 to 10
For counter As Integer = 2 To 10
outputLabel.Text &= counter & " "
Next
Result: 2, 3, 4, 5, 6, 7, 8, 9, 10

7. General Form of a For … Next Statement
For initialization To finalValue Step increment
statement
Next

8. Other Examples of For … Next (1)
Declaring the control variable before a For…Next Statement
Dim counter As Integer
For counter = 2 To 10 Step 2
outputLabel.Text &=counter & " "
Next
Using expressions in the For…Next statement
For j As Integer = x To 4*x*y Step y \ x

9. Other Examples of For … Next (2)
Default increment: 1
For i = 1 To 100
For i = 1 To 100 Step 1
Decrement
For i = 100 To 1 Step -1

10. Example 5.5: InterestCalculator.vb
URL:

11. Example 5.5: InterestCalculator.vb (cont'd)
NumericUpDown control
Minimum property
Maximum property
Increment property
Value property

12. Example 5.5: InterestCalculator.vb (cont'd)
Val(…) function
Convert strings to numbers
Dim principal As Decimal = Val(principalTextBox.Text)
Ignores white space in the string
E.g. " " will be converted to 335
vbTab
Format by adding a tab

13. Example 5.5: InterestCalculator.vb (cont'd)
String.Format("{0:C}", amount)
Output variable amount in currency format
E.g., $1,050.00
TextChanged event of controls TextBox and NumericUpDown
resultListBox.Items.Clear()

14. Nested Repetition Statements
For i = 1 To 10 Step 1
For j = 1 To 20 Step 2 …
Next i
Next j

15. Example 5.8: SquareOfCharacters.vb
URL:

16. Example 5.8: SquareOfCharacters.vb (cont'd)
For row As Integer = 1 To sideLength
For column As Integer = 1 To sideLength
outputTextBox.AppendText(fillCharacter & " ")
Next column
outputTextBox.AppendText(vbCrLf)
Next row

17. Do…Loop While and Do…Loop Until Repetition Statements
The loop body is always executed at least once
Dim product As Integer = 1 Do
product = product * 3
Loop While product <=100
Loop Until product >100

18. Use Exit to Terminate Repetition Statements
Exit Do
Terminate the repetition statements such as:
Do While…Loop, Do Until…Loop, Do…Loop While, Do…Loop Until
Exit For
Terminate For…Next
Exit While
Terminate While…End While
Exit Select
Terminate Select…Case

19. Use Continue in Repetition Statements
Continue statement only terminates the current iteration
Continue Do
Terminate the repetition statements such as:
Do While…Loop, Do Until…Loop, Do…Loop While, Do…Loop Until
Continue For
Terminate For…Next
Continue While
Terminate While…End While

20. In the Last Class: Selection Structure
If … Then
If … Then … Else
Select … Case
[grade>=60]
display "passed"
[grade<60]

21. Multiple-Selection Statement: Select … Case
Select Case grade Case 100 perfectScoreCount += 1 ' increment perfectScoreCount aCount += 1 ' increment aCount Case 90 To 99 ' grade was between 90 and 99 Case 80 To 89 ' grade was between 80 and 89 bCount += 1 ' increment bCount Case 70 To 79 ' grade was between 70 and 79 cCount += 1 ' increment cCount Case 60 To 69 ' grade was between 60 and 69 dCount += 1 ' increment dCount Case Else ' grade was less than 60 fCount += 1 ' increment fCount End Select

22. Multiple-Selection Statement: Select … Case
Case Else is optional
If no case matches and there is no Case Else, then program control continues with the first statement after Select … Case
End Select terminates the Select … Case statement

23. Example 5.9: ClassAverage.vb
URL:
TextBox
gradeTextBox.Focus()
gives the focus to the
gradeTextBox
String.Empty

24. Expression 1 And Expression 2
Logical Operators
Logical And operator
If gender = "F" And age >=65 Then
seniorFemales += 1
End If
Expression 1
Expression 2
Expression 1 And Expression 2
False
True

25. Logical Operators (cont'd)
Logical Or Operator
Expression 1
Expression 2
Expression 1 Or Expression 2
False
True

26. Short-Circuit Evaluation
AndAlso
If gender = "F" AndAlso age >=65
If gender is not "F", then "age >=65" will not be evaluated
OrElse
If gender = "F" OrElse age >=65
If gender is "F", then "age >=65" will not be evalutated

27. Other Logical Operators
Logical Xor operator
Logical Not operator
If Not (value = 0) Then …
Expression 1
Expression 2
Expression 1 Xor Expression 2
False
True

28. Rules of Operator Precedence
priority ^
+, - (sign operations)
*, / \
Mod
+, - (addition and subtraction)
&
=, <>, <, <=, >, >= (equality and relational)
Not
And, AndAlso
Or, OrElse
Xor
=, +=, -=, *=, /=, \=, ^=, &=
high
low