Integer to Ordinal Extension

C# extension method to convert an integer to it's ordinal string representation. For example, the integer value 23 would become "23rd".

using System;

namespace Exceptionless.Core.Extensions
{
    public static class IntExtensions
    {
        public static string ToOrdinal(this int num)
        {
            switch (num % 100)
            {
                case 11:
                case 12:
                case 13:
                    return num.ToString("#,###0") + "th";
            }

            switch (num % 10)
            {
                case 1:
                    return num.ToString("#,###0") + "st";
                case 2:
                    return num.ToString("#,###0") + "nd";
                case 3:
                    return num.ToString("#,###0") + "rd";
                default:
                    return num.ToString("#,###0") + "th";
            }
        }
    }
}