Lesson 8 : Select Case....End select Control Structure

In the previous lesson, we have learned how to control the program flow using the If...ElseIf control structure. In this chapter, you will learn another way to control the program flow, that is, the Select Case control structure. However, the Select Case control structure is slightly different from the If....ElseIf control structure . The difference is that the Select Case control structure basically only make decision on one expression or dimension (for example the examination grade) while the If ...ElseIf statement control structure may evaluate only one expression, each If....ElseIf statement may also compute entirely different dimensions. Select Case is preferred when there exist many different conditions because using If...Then..ElseIf statements might become too messy.

The format of the Select Case control structure is show below:

Select Case expression

Case value1
Block of one or more VB statements
Case value2
Block of one or more VB Statements
Case value3
.
.
Case Else
Block of one or more VB Statements

End Select

Example 8.1

Dim grade As String

Private Sub Compute_Click( )

grade=txtgrade.Text

Select Case grade

Case "A"
result.Caption="High Distinction"

Case "A-"
result.Caption="Distinction"

Case "B"
result.Caption="Credit"

Case "C"
result.Caption="Pass"

Case Else
result.Caption="Fail"

End Select

End Sub

Example 8.2

Dim mark As Single

Private Sub Compute_Click()
'Examination Marks

mark = mrk.Text

Select Case mark

Case Is >= 85

comment.Caption = "Excellence"

Case Is >= 70

comment.Caption = "Good"

Case Is >= 60

comment.Caption = "Above Average"

Case Is >= 50

comment.Caption = "Average"

Case Else

comment.Caption = "Need to work harder"

End Select

End Sub

Example 8.3

Example 8.2 could be rewritten as follows:

Dim mark As Single

Private Sub Compute_Click()

'Examination Marks

mark = mrk.Text

Select Case mark

Case 0 to 49

comment.Caption = "Need to work harder"

Case 50 to 59

comment.Caption = "Average"

Case 60 to 69

comment.Caption = "Above Average"

Case 70 to 84

comment.Caption = "Good"

Case Else

comment.Caption = "Excellence"

End Select

End Sub

*VbTutor Lesson 8