c# switch problem

Question

I'm new to programming and having a problem with the following code:

    private string alphaCoords(Int32 x)
    {
        char alphaChar;

        switch (x)
        {
            case 0: alphaChar = 'A'; break;
            case 1: alphaChar = 'B'; break;
            case 2: alphaChar = 'C'; break;
            case 3: alphaChar = 'D'; break;
            case 4: alphaChar = 'E'; break;
            case 5: alphaChar = 'F'; break;
            case 6: alphaChar = 'G'; break;
            case 7: alphaChar = 'H'; break;
            case 8: alphaChar = 'I'; break;
            case 9: alphaChar = 'J'; break;
        }

        return alphaChar.ToString();
    }

The compiler says: Use of unassigned local variable 'alphaChar'

But I'm assigning it in my switch block.

I'm sure this is my fault as I dont know enough about programming.

Please advise.

Thanks.

Answer 1

You're assigning it if x is 0-9. What would you expect it to do if x were 123 though? While you may know that only values between 0 and 9 will be passed in, the compiler doesn't - so it needs to consider what would happen otherwise.

One way to avoid this is to have a default case in your switch statement, which you can use to throw an exception if the value isn't in the expected range:

switch (x)
{
    case 0: alphaChar = 'A'; break;
    case 1: alphaChar = 'B'; break;
    case 2: alphaChar = 'C'; break;
    case 3: alphaChar = 'D'; break;
    case 4: alphaChar = 'E'; break;
    case 5: alphaChar = 'F'; break;
    case 6: alphaChar = 'G'; break;
    case 7: alphaChar = 'H'; break;
    case 8: alphaChar = 'I'; break;
    case 9: alphaChar = 'J'; break;
    default: throw new ArgumentOutOfRangeException();
}

Here's a slightly simpler alternative though, which removes your switch statement completely:

if (x < 0 || x > 9)
{
    throw new ArgumentOutOfRangeException();
}
char alphaChar = (char)('A' + x);

Note that you do need to exercise care when using arithmetic like this. In Java and C# the underlying representation is guaranteed to be Unicode, which makes life a lot easier. I believe it's fine for things like this (and hex parsing/formatting) but when you venture into more exotic scenarios it would fail. Then again, that's true for a lot of code simplification techniques... if they're applied inappropriately, you end up with a mess.

Answer 2

The compiler is complaining because alphaChar is possibly undefined -- if it is not one of the values in your switch then it will not have been defined. You can do one of the following things:

• Set an initial value of char which will be carried through if none of the switch conditions is true.
• Add a "default" clause to your switch statement.

Answer 3

Before its first use local variable must be definitely assigned (according to C# specification rules). In this particular case switch construct doesn't guarantee that alphaChar will be definitely assigned thus compiler error. You can provide initial value to alphaChar and thus it will be definitely assigned.