Enumerations with and without values

Question

I have an enumeration and a switch statement based on that enum, which looks like this:

public enum MyEnum
    {
        VAL1,
        VAL2,
        VAL3,
        ONE = 1,
        TWO = 2
    }

and the switch:

switch ((MyEnum)Enum.Parse(typeof(MyEnum), input.ToUpper()))
        {
            case MyEnum.VAL1:
                Console.WriteLine("val1");
                break;
            case MyEnum.VAL2:
                Console.WriteLine("val2");
                break;
            case MyEnum.VAL3:
                Console.WriteLine("val3");
                break;
            case MyEnum.ONE:
                Console.WriteLine("1");
                break;
            default:
                Console.WriteLine("default");
                break;
        }

where input is a string. The problem I have is that I have a compiler error,

The label 'case 1:' already occurs in the switch statement

I found that moving the 'ONE' element as first in the enumeration resolves the issue, but my question is why this happens?

Answer 1

Well because what happens is when you have:

public enum MyEnum
    {
        VAL1,
        VAL2,
        VAL3,
        ONE = 1,
        TWO = 2
    }

You basically have:

public enum MyEnum
    {
        VAL1 = 0,
        VAL2 = 1,
        VAL3 = 2,
        ONE = 1,
        TWO = 2
    }

You see where your problem is, now? You need to assign them different values.

Answer 2

When creating a new enum, its options are actually numbers. If you don't define a specific numeric value to an enum option, the compiler set it by default in an ascending order (0,1,2,...). this is why VAL1=0, VAL2=1 and VAL3=2. then you set a value to ONE=1 and TWO=2 and so you have to different names to the same option (VAL2=ONE=1 and VAL3=TWO=2). a simple console application demonstrates it: example