Question

Found this code in one of our classes but I am not understanding what the first case statement is doing: “Case i = 1”. I am sure that someone just incorrectly converted this from an IF/ELSE statement but why is VB.NET allowing this syntax. What does it mean when it is written this way?

    Dim i As Integer = 1
    Select Case i
        Case i = 1
            Return True
        Case Else
            Return False
    End Select

Answer 1

In short the code is effectively doing the following

If i = (i = 1) Then
  Return True
Else
  Return False
End If

The Case expression in a VB.Net Select .. Case statement comes in 3 different forms.

1. Case expr1 To expr2
2. Case Is comparisonOp expr
3. Case expr

This example is the 3rd version of the Case operator. Implicitly the compiler will evaluate the expression testExpr = expr for that Case statement. In this case (haha) it comes out to i = (i = 1)

• Reference

Note: When run the conditional will actually evaluate to false and hence the else block will be run. The reason why is the expression is actually evaluated as

i = CInt(i = 1)

The i = 1 portion will evaluate to True and due to legacy reasons from VB6 (and COM’s version of TRUE) the CInt(True) portion will evaluate to -1 and hence the comparison will fail.