Visual Basic 2008 Tutorial
Lesson 10: Select Case 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.
10.1 The Select Case...End Select Structure
The format of the Select Case control structure is show below:
Select Case test expression
Case expression list 1
Block of one or more VB statements
Case expression list 2
Block of one or more VB Statements
Case expression list 3
Block of one or more VB statements
Case expression list 4
.
.
.
Case Else
Block of one or more VB Statements
End Select
Example 10.1
' Examination Grades
Dim grade As String
Private Sub Compute_Click( )
grade=txtgrade.Text
Select Case grade
Case "A"
Label1.Text="High Distinction"
Case "A-"
Label2.Text="Distinction"
Case "B"
Label3.Text="Credit"
Case "C"
Label4.Text="Pass"
Case Else
Label5.Text="Fail"
End Select
Example 10.2
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In this example, you can use the keyword Is together with the comparison operators.
Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
'Examination Marks
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Dim mark As Single
mark = mrk.Text
Select Case mark
Case Is >= 85
Label1.Text= "Excellence"
Case Is >= 70
Label2.Text= "Good"
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Case Is >= 60
Label3.Text = "Above Average"
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Case Is >= 50
Label4.Text= "Average"
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Case Else
Label5.Text = "Need to work harder"
End Select
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End Sub
Example 10.3
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Example 10.2 could be rewritten as follows:
Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
'Examination Marks
Dim mark As Single
mark = mrk.Text
Select Case mark
Case 0 to 49
Label1.Text = "Need to work harder"
Case 50 to 59
Label2.Text = "Average"
Case 60 to 69
Label3.Text= "Above Average"
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Case 70 to 84
Label4.Text = "Good"
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Case Else
Label5.Text= "Excellence"
End Select
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End Sub
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source : http://www.vbtutor.net/vb2008/vb2008tutor.html
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