Visual Basic 2013 Lesson 14: Making Decisions using Select Case

[Lesson 13] << [Contents] >> [Lesson 15]

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 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 Visual Basic 2013 statements
Case expression list 2
Block of one or more Visual Basic 2013 Statements
Case expression list 3
.
.
Case Else
Block of one or more Visual Basic 2013 StatementsEnd 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

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:

Figure 14.1

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