C# using numbers in an enum

This is a valid enum

public enum myEnum
{
  a= 1,
  b= 2,
  c= 3,
  d= 4,
  e= 5,
  f= 6,
  g= 7,
  h= 0xff
};

But this is not

public enum myEnum
{
  1a = 1,
  2a = 2,
  3a = 3,
};

Is there a way I can use an number in a enum? I a开发者_运维技巧lready have code that would populate dropdowns from enums so it would be quite handy

No identifier at all in C# may begin with a number (for lexical/parsing reasons). Consider adding a [Description] attribute to your enum values:

public enum myEnum
{
    [Description("1A")]
    OneA = 1,
    [Description("2A")]
    TwoA = 2,
    [Description("3A")]
    ThreeA = 3,
};

Then you can get the description from an enum value like this:

((DescriptionAttribute)Attribute.GetCustomAttribute(
    typeof(myEnum).GetFields(BindingFlags.Public | BindingFlags.Static)
        .Single(x => (myEnum)x.GetValue(null) == enumValue),    
    typeof(DescriptionAttribute))).Description

Based on XSA's comment below, I wanted to expand on how one could make this more readable. Most simply, you could just create a static (extension) method:

public static string GetDescription(this Enum value)
{
    return ((DescriptionAttribute)Attribute.GetCustomAttribute(
        value.GetType().GetFields(BindingFlags.Public | BindingFlags.Static)
            .Single(x => x.GetValue(null).Equals(value)),
        typeof(DescriptionAttribute)))?.Description ?? value.ToString();
}

It's up to you whether you want to make it an extension method, and in the implementation above, I've made it fallback to the enum's normal name if no [DescriptionAttribute] has been provided.

Now you can get the description for an enum value via:

myEnum.OneA.GetDescription()

No, there isn't. C# does not allow identifiers to start with a digit.

Application usability note: In your application you should not display code identifiers to the end-user anyway. Think of translating individual enumeration items into user-friendly displayable texts. Sooner or later you'll have to extend the enum with an item whose identifier won't be in a form displayable to the user.

UPDATE: Note that the way for attaching displayable texts to enumeration items is being discusses, for example, here.

An identifier in C# (and most languages) cannot start with a digit.

If you can modify the code that populates a dropdown with the enumeration names, you could maybe have a hack that strips off a leading underscore when populating the dropdown and define your enum like so:

public enum myEnum
{
  _1a = 1,
  _2a = 2,
  _3a = 3
};

Or if you don't like the underscores you could come up with your own 'prefix-to-be-stripped' scheme (maybe pass the prefix to the constructor or method that will populate the dropdown from the enum).

No way. A valid identifier (ie a valid enumeration member) cannot start with a digit.

Enumerations are no different than variables in terms of naming rules. Therefore, you can't start the name with a number. From this post, here are the main rules for variable naming.

• The name can contain letters, digits, and the underscore character (_).

  • The first character of the name must be a letter. The underscore is also a legal first character, but its use is not recommended at the beginning of a name. An underscore is often used with special commands, and it's sometimes hard to read.

  • Case matters (that is, upper- and lowercase letters). C# is case-sensitive; thus, the names count and Count refer to two different variables.

  • C# keywords can't be used as variable names. Recall that a keyword is a word that is part of the C# language. (A complete list of the C# keywords can be found in Appendix B, "C# Keywords.")

Identifiers can't start with numbers. However, they can contain numbers.

Short and crisp 4 line code.

We simply use enums as named integer for items in code,

so any simplest way is good to go.

public enum myEnum
{
    _1 = 1,
    _2,
    _3,
};

Also for decimal values,

public enum myEnum
{
    _1_5 = 1,
    _2_5,
    _3_5,
};

So while using this in code,

int i = cmb1.SelectedIndex(0); // not readable
int i = cmb1.SelectedIndex( (int) myEnum._1_5); // readable

Here is what i came up with as an alternative, where I needed Enums to use in a "for" Loop and a string representation equivalent to use in a Linq query.

1. Create enums namespace to be used in "for" Loop.

public enum TrayLevelCodes
    {
        None,
        _5DGS,
        _5DG,
        _3DGS,
        _3DG,
        _AADC,
        _ADC,
        _MAAD,
        _MADC
    };

2. Create strings based on enum created to be used for Linq query

public string _5DGS = "\"5DGS\"",
        _5DG = "\"5DG\"",
        _3DGS = "\"3DGS\"",
        _3DG = "\"3DG\"",
        _AADC = "\"AADC\"",
        _ADC = "\"ADC\"",
        _MAAD = "\"MAAD\"",
        _MADC = "\"MADC\"";

3. Create function that will take an enum value as argument and return corresponding string for Linq query.

public string GetCntnrLvlDscptn(TrayLevelCodes enumCode)
        {
            string sCode = "";
            switch (enumCode)
            {
                case TrayLevelCodes._5DGS:
                    sCode = "\"5DGS\"";
                    break;
                case TrayLevelCodes._5DG:
                    sCode = "\"5DG\"";
                    break;
                case TrayLevelCodes._3DGS:
                    sCode = "\"3DGS\"";
                    break;
                case TrayLevelCodes._3DG:
                    sCode = "\"3DG\"";
                    break;
                case TrayLevelCodes._AADC:
                    sCode = "\"AADC\"";
                    break;
                case TrayLevelCodes._ADC:
                    sCode = "\"AAC\"";
                    break;
                case TrayLevelCodes._MAAD:
                    sCode = "\"MAAD\"";
                    break;
                case TrayLevelCodes._MADC:
                    sCode = "\"MADC\"";
                    break;
                default:
                    sCode = "";
                    break;
            }
                return sCode;
        }

4. Here is how i am using what i created above.

for (var trayLevelCode = TrayLevelCodes._5DGS; trayLevelCode <= TrayLevelCodes._MADC; trayLevelCode++)
{
    var TrayLvLst = (from i in pair1.Value.AutoMap
                     where (i.TrayLevelCode == HTMLINFO.GetCntnrLvlDscptn(trayLevelCode))
                     orderby i.TrayZip, i.GroupZip
                     group i by i.TrayZip into subTrayLvl
                     select subTrayLvl).ToList();
    foreach (DropShipRecord tray in TrayLvLst)
    {

    }
}