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 can 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

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