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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

    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 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