Consider adding a default fall through for Select Case and Switch statements.

Remarks

Select Case statements should generally have a default fall through to handle unanticipated test expression results. Without a default fall through, code that does not meet anticipated results will simply do nothing and continue execution after the Select Case statement.

The following code handles for string values of '+', '-', and '*'. However, if another value is passed (for example, '/'), the Select Case statement does nothing:

    ' VB
    Select Case mathFunction
        Case "+"
            Add(num1, num2)
        Case "-"
            Subtract(num1, num2)
        Case "*"
            Multiply(num1, num2)
    End Select

    // C#
    switch(mathFunction)       
    {         
        case "+":
            Add(num1, num2);
            break;
        case "-":
            Subtract(num1, num2);
            break;
        case "*":
            Multiply(num1, num2);          
            break;      
    }

Resolution

You should either add default code to handle unanticipated conditions, or at a minimum, add a comment stating that the condition could not happen. In Visual Basic, use a Case Else statement. In C#, use the default keyword. For example, you could revise the code above to show an error if it encounters an unanticipated result:

    ' VB
    Select Case mathFunction
        Case "+"
            Add(num1, num2)
        Case "-"
            Subtract(num1, num2)
        Case "*"
            Multiply(num1, num2)
        Case Else
            Console.WriteLine("Only +, -, and * are handled.")
    End Select

    // C#
    switch(mathFunction)       
    {         
        case "+":
            Add(num1, num2);
            break;
        case "-":
            Subtract(num1, num2);
            break;
        case "*":
            Multiply(num1, num2);          
            break;      
        default: 
            Console.WriteLine("Only +, -, and * are handled.");
            break; 
    }

See Also

VB Select Case Statement

C# switch statement