using System;
using System.Collections.Generic;
using System.Linq;
public class Program
{
public static void Main()
string fname = "a";
string lname = "";
List<string> names = new List<string>{fname.Trim(), lname.Trim()};
string fullname = String.Join(",", names.Where(s=>!string.IsNullOrWhiteSpace(s)).ToList());
Console.WriteLine(fullname);
}