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VB2010 Lesson 10- Using Select Case

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 multiple conditions because using If...Then..ElseIf statements will become too messy. 10.1 The Select Case...End Select Structure The format of the Select Case control structure is as followss: 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 10.2 The usage of Select Case is shown in the following exampless 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-"        Label1.Text="Distinction"    Case "B"          Label1.Text="Credit"    Case "C"          Label1.Text="Pass"    Case Else          Label1.Text="Fail"    End Select Example 10.2   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  Dim mark As Single  mark = mrk.Text     Select Case mark  Case Is >= 85          Label1.Text= "Excellence" Case Is >= 70         Label2.Text= "Good" Case Is >= 60    Label3.Text = "Above Average" Case Is >= 50 Label4.Text= "Average" Case Else Label5.Text = "Need to work harder" End Select End Sub   Example 10.3   Example 10.2 can 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 = Textbox1.Text     Select Case mark  Case 0 to 49         Label1.Text = "Need to work harder"   Case 50 to 59        Label1.Text = "Average" s  Case 60 to 69    Label1.Text= "Above Average" Case 70 to 84 Label1.Text = "Good" Case 85 to 100 Label1.Text= "Excellence" Case Else Label1.Text= "Wrong entry, please reenter the mark" End Select   End Sub     Example 10.4 Grades in high school are usually presented with a single capital letter such as A, B, C, D or E. The grades can be computed as follow: Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click 'Examination Marks Dim mark As Single mark = TextBox1.Text Select Case mark Case 0 To 49 Label1.Text = "E" Case 50 To 59 Label1.Text = "D" Case 60 To 69 Label1.Text = "C" Case 70 To 79 Label1.Text = "B" Case 80 To 100 Label1.Text = "A" Case Else Label1.Text = "Error, please reenter the mark" End Select End Sub The output of Example 10.4           Copyright  2010  Dr.Liew Voon Kiong . All rights reserved |Contact: admin@vbtutor.net [Privacy Policy]