Visual Basic 2017 Lesson 14: Using Select Case

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In this lesson, you shall learn how to use the Select Case control structure in Visual Basic 2017. The Select Case control structure also involves decisions making but it slightly different from the If….ElseIf control structure . The If … Then…ElseIf statement control structure evaluates only one expression but each ElseIf statement computes different values for the expression. On the other hand, the Select Case control structure evaluates one expression for multiple values. Select Case is preferred when there exist multiple conditions as using If…Then..ElseIf statements will become too messy.



14.1 The Select Case…End Select Structure

The structure of the Select Case control structure in Visual Basic 2017 is as follows:

Select Case expression
Case value1
Block VB statements
Case value2
Block VB Statements
Case value3
.
.
Case Else
Block VB Statements

End Select

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

Example 14.1: Examination Grades

In this example, the program will display a message associated with the grade entered by the user.

The Code

Private Sub BtnShow_Click(sender As Object, e As EventArgs) Handles BtnShow.Click
Dim grade As String
grade = TxtGrade.Text
Select Case grade
Case “A”
MsgBox(”High Distinction”)
Case “A-”
MsgBox(”Distinction”)
Case “B”
MsgBox(”Credit”)
Case “C”
MsgBox(”Pass”)
Case Else
MsgBox(”Fail”)End Select
End Sub

The Output

vb2015_fig14.1

 Figure 14.1




vb2015_fig14.2

Figure 14.2

In this example, you can use the keyword Is together with the comparison operators to evaluate an expression.

Example 14.2

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
MsgBox( “Excellence”)
Case Is >= 70
MsgBox( “Good”)
Case Is >= 60
MsgBox( “Above Average”)
Case Is >= 50
MsgBox( “Average”)
Case Else
MsgBox( “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
MsgBox( “Need to work harder”)
Case 50 to 59
MsgBox( “Average” )
Case 60 to 69
MsgBox( “Above Average”)
Case 70 to 84
MsgBox( “Good”)
Case 85 to 100
MsgBox(“Excellence”)
Case Else
MsgBox( “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
LblGrade.Text = “E”
Case 50 To 59
LblGrade.Text = “D”
Case 60 To 69
LblGrade.Text = “C”
Case 70 To 79
LblGrade.Text = “B”
Case 80 To 100
LblGrade.Text = “A”
Case Else
LblGrade.Text = “Error, please re-enter the mark”
End Select
End Sub

The output:

Figure 14.3




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