lesson 14 Select Case

In this lesson, you will learn how to use the Select Case control structure in Visual Basic 2013  to control the program flow. The Select Case control structure is slightly different from the I....then...Else control structure. The difference is that the Select Case control structure basically only make a decision on one expression or dimension. On the other hand, the If...Then...Else statement may evaluate only one expression, each If statement may also compute entirely different dimensions. Select Case is preferred when there exist multiple conditions as using If…Then..ElseIf statements will become too complicated.

14.1 The Select Case…End Select Structure

The structure of the Select Case control structure in is as follows:

Select Case test expressionCase expression list 1
Block of one or more statements
Case expression list 2
Block of one or more Statements
Case expression list 3
.
.
Case Else
Block of one or more Statements
End Select

14.2 The usage of Select Case is shown in the following examples

Example 14.1: 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
End Sub

Example 14.2

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 14.3

Example 14.2 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 14.4

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: