CODEWITHSUNDEEP
vb.netsyntaxswitch-statement
Llyle
Llyle

Reputation: 6166

What is the VB.NET select case statement logic with case OR-ing?

I'm using an Or statement in my case expression.

Even though I have a value within this range, it didn't find a match. Why not?

Example Code:

Select Case 2
    Case 0
        ' Some logic

    Case 1
        ' Some other logic

    Case 2 Or 3
        Console.WriteLine("hit")

 End Select

With the above I would assume that hit would be printed, but that's not the case.

Upvotes: 60

Views: 79889

Answers (6)

Regular Jo
Regular Jo

Reputation: 5510

Most or all of these answers are ignoring the purpose of fall-through (or Goto Case):

Not having to reuse code or create a special function just for a few areas in the same Select Case/If Tree so that you can avoid reusing code, like this Javascript.

These samples are pretty contrived. There are definitely ways to simplify this scenario, but a lot of times, there aren't.

let pay = 100, perks = '';
Switch (EmpObj.type) {
  Case 'Boss':
    pay = pay * 10;
    perks = '11 month vacation per year';
  Case 'Manager':
    pay = pay * 3; // This will make Boss pay * 30
  Case 'Employee':
    EmpObj.pay = pay;
    EmpObj.perks = perks;
    break;
  Case 'Intern':
    EmpObj.sendMessage("Go get some coffee.")
}

In VB.net, the same code would be

dim pay = 100, perks = "";
Switch (EmpObj.type) {
  Case "Boss":
    pay = pay * 30
    perks = "11 month vacation per year"
  Case "Manager":
    pay = pay * 3
  Case "Employee":
  Case 'Intern':
    pay = 0
    EmpObj.sendMessage("Go get some coffee.")
End Select

EmpObj.pay = pay;
EmpObj.perks = perks;

Case, in simple situations, is easier to read and write than a comparative if-branch, but the fall-through is the best part.

There's a way that works now at least in Visual Basic 2017. It's not the prettiest though.

GoTo Case "[label]" and Goto [Case-label] still do not work.

The label (Number2 here) must be after the Case. That was the most disappointing part.

dim Value = "1"
Select Case Value
    Case "0"
       ' do nothing, example
    Case "1"
        MsgBox("one")
        GoTo Number2
    Case "2"
Number2:
        MsgBox("two")
    Case "boolean"
        MsgBox("three")
        ' just to show it won't fall through
End Select

Upvotes: 0

John T
John T

Reputation: 470

As Jared said, you need to use the comma operator to delimit case statements.

The Or you were doing is a bitwise OR, resulting in it being "3". Amusingly, "2 AND 3" would probably have worked for your specific case.

Upvotes: 24

user67143
user67143

Reputation: 327

Edit: It appears I was wrong in assuming that VB.NET doesn't allow Case ORing. I was thinking in C# and IL and it appears I was wrong.

However, as someone pointed out, the reason your code did not work was because Case 2 Or 3 was evaluating 2 Or 3 as a bitwise or and hence evaluating to Case 3.

For clarification: 


       2 binary = 0000 0010
       3 binary = 0000 0011
  2 Or 3 binary = 0000 0011 (= 3)


  Select Case 2
     Case 0            '--> no match

     Case 1            '--> no match

     Case 2 Or 3       '(equivalent to Case 3  --> no match)
   End Select

However, I feel that I should point out that for the sake of performance, one should not use such constructs. When the compiler encounters Select statements (switch in C#) it will try to compile them using lookup tables and the switch MSIL instruction but in the case where you have something like Case 1,2,11,55 the compiler will not be able to convert that to a lookup table and it will have to use a series of compares (which is like using If.. Else).

The point is that in order to really take advantage of the Select statement, the cases should be designed with that in mind. Otherwise, the only benefit is code readability.

A well designed switch is an O(1) operation whereas an poorly designed one (which is equivalent to a series of If..Then..Else statements) is an O(n) operation.

Upvotes: 10

Restore The Data Dumps Again
Restore The Data Dumps Again

Reputation: 39335

JaredPar has it right but you can also use the To construct

Select Case 2
    Case 0,1
    Case 2 To 3
        Console.WriteLine("Hit")
End Select

This would be 0 or 1 do nothing, 2 or 3 print Hit...The To construct is a range...

Here's the MSDN

Upvotes: 21

achinda99
achinda99

Reputation: 5078

This will allow you to perform "something" in the case of 0, "something else" in the case of 1, "hit" in the case of 2 or 3 or "hit else" otherwise. 

Select Case 2
    Case 0
        Console.WriteLine("something")
    Case 1
        Console.WriteLine("something else")
    Case Is 2 To 3
        Console.WriteLine("hit")
    Else
        Console.WriteLine("hit else")
 End Select

Upvotes: 3

JaredPar
JaredPar

Reputation: 754763

Use the comma operator to delimit case statements

Select Case 2
    Case 0,1,2,3
        Console.WriteLine("hit")
 End Select

Upvotes: 104

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