Select Case

Select Case compares one value against several cases — clearer than a long chain of ElseIfs:

Module Program
    Function Describe(n As Integer) As String
        Select Case n
            Case 0
                Return "zero"
            Case 1, 2, 3
                Return "small"
            Case 4 To 9
                Return "medium"
            Case Is < 0
                Return "negative"
            Case Else
                Return "large"
        End Select
    End Function

    Sub Main()
        For Each n In {0, 2, 7, -5, 100}
            Console.WriteLine($"{n}: {Describe(n)}")
        Next
    End Sub
End Module

0: zero
2: small
7: medium
-5: negative
100: large

• A case can list values (1, 2, 3), a range (4 To 9), or a comparison (Is < 0).
• Only the first matching case runs — there's no fall-through, so no break is needed.
• Case Else handles everything not matched.

Strings and other types

Module Program
    Sub Main()
        For Each dayName In {"Saturday", "Monday", "Holiday"}
            Select Case dayName
                Case "Saturday", "Sunday"
                    Console.WriteLine($"{dayName}: weekend")
                Case "Monday", "Tuesday", "Wednesday", "Thursday", "Friday"
                    Console.WriteLine($"{dayName}: weekday")
                Case Else
                    Console.WriteLine($"{dayName}: unknown")
            End Select
        Next
    End Sub
End Module

Saturday: weekend
Monday: weekday
Holiday: unknown

Ranges work on strings too, but alphabetically: Case "A" To "M" matches any text that sorts between "A" and "M". A range like "Monday" To "Friday" would match nothing at all, because "Friday" sorts before "Monday" — so list the day names explicitly, as above.

Select Case True

A common VB idiom tests unrelated conditions in order:

Module Program
    Sub Main()
        Dim bmi = 23.4
        Select Case True
            Case bmi < 18.5
                Console.WriteLine("underweight")
            Case bmi < 25
                Console.WriteLine("normal")
            Case Else
                Console.WriteLine("overweight")
        End Select
    End Sub
End Module

normal

Practice

Write a function DaysInMonth(month As Integer) As Integer for a non-leap year using Select Case, and print the result for months 2, 4, and 12.

Module Program
    Function DaysInMonth(month As Integer) As Integer
        Select Case month
            Case 2
                Return 28
            Case 4, 6, 9, 11
                Return 30
            Case Else
                Return 31
        End Select
    End Function

    Sub Main()
        For Each m In {2, 4, 12}
            Console.WriteLine($"Month {m}: {DaysInMonth(m)} days")
        Next
    End Sub
End Module

Month 2: 28 days
Month 4: 30 days
Month 12: 31 days