Lesson 8 : More On Program Control

8.1 Select Case
If you have a lot of conditional statements, using If..Then..Else could be very messy. For multiple conditional statements, it is better to use Select Case

The format is :

Select Case expression

Case value1
Block of one or more VB statements
Case value2
Block of one or more VB Statements
Case value3
Block of one or more VB statements
Case value4
.
.
.
Case Else
Block of one or more VB Statements

End Select

* The data type specified in expression must match that of Case values.





8.2 Examples
Example 8.1

' Examination Grades

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

*Please note that grade is a string, so all the case values such as "A" are of String data type.


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

* Note we use the keyword Is here to impose the conditions. This is generally used for numeric data.


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