switch statement in C# and "a constant value is expected"

Question

Why does the compiler say "a constant value is required" for the first case...the second case works fine...

switch (definingGroup)
{
    case Properties.Settings.Default.OU_HomeOffice:  
        //do something  
        break;
    case "OU=Home Office":  
        //do something
        break;
    default:
        break;
 }

also tried...

switch (definingGroup)
{
    case Properties.Settings.Default.OU_HomeOffice.ToString():  
        //do something
        break;
    case "OU=Home Office":
        //do something
        break;
    default:
        break;
 }

...same error

Here's the Properties.Setting code

[global::System.Configuration.ApplicationScopedSettingAttribute()]
[global::System.Diagnostics.DebuggerNonUserCodeAttribute()]
[global::System.Configuration.DefaultSettingValueAttribute("OU=Home Office")]
public string OU_HomeOffice {
    get {
        return ((string)(this["OU_HomeOffice"]));
    }
}

Answer 1

Properties.Settings.Default.OU_HomeOffice isn't a constant string - something known at compile time. The C# switch statement requires that every case is a compile-time constant.

(Apart from anything else, that's the only way it can know that there won't be any duplicates.)

See section 8.7.2 of the C# 3.0 spec for more details.

Answer 2

This is because the value cannot be determined at compile time (as it is coming out of a configuration setting). You need to supply values that are known at the time the code is compiled (constants).