using System;

using System.Linq;

public class Program

{

    public static void Main()

    {

        var arr = new String[] {null, null, "hi", "bye", null};

​

        Console.WriteLine(arr[0] ?? arr[1] ?? arr[2] ?? arr[3] ?? arr[4]);

        Console.WriteLine(arr.FirstOrDefault(str => str != null));

    }

}