Select Case

The If...Then...ElseIf control structure evaluates one expression through multiple separate conditions. In contrast, the Select Case structure evaluates one expression once, then compares it to many possible values or ranges.

Select Case is usually easier to read when:

• One variable must be checked against many possible values.
• You want cleaner and more organized decision-making code.
• You are matching ranges such as exam marks, categories, or options.

The basic structure of Select Case in Visual Basic 2015 is:

Select Case expression
    Case value1
        Statements
    Case value2
        Statements
    Case value3
        Statements
    Case Else
        Statements
End Select

Visual Basic evaluates the expression once and then checks which Case matches. If none of the listed cases match, the statements in Case Else will run.

In this example, the program displays a message associated with the grade entered by the user. This is a good use of Select Case because one input value, the grade, may match several possible cases.

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

This program checks the text entered by the user and displays a message according to the grade.

In Select Case, you may use the keyword Is together with comparison operators to test numeric ranges.

Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
    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

In this example, the mark is tested from top to bottom. As soon as one condition matches, Visual Basic executes that case and stops checking the rest.

Example 14.2 can also be written using numeric ranges, which often makes the logic easier to read:

Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
    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 re-enter the mark")
    End Select
End Sub

This form is very useful for classifying numbers into clear ranges such as marks, ages, prices, or categories.

Grades in schools are often represented by letters such as A, B, C, D, or E. The following program takes a mark entered by the user and assigns a letter grade.

Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
    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

This is a practical example of how Select Case can simplify classification tasks.

Both Select Case and If...ElseIf are used for decision making, but they are best suited for different situations.

• Use If...ElseIf when different expressions or more flexible logic are needed.
• Use Select Case when one expression is tested against many values or ranges.
• Select Case often makes your code easier to read and maintain.