using System;

using System.Linq;

​

public class Program

{

    public static void Main()

    {

        Person[] people = {

            new Person(){ FirstName="Steve", LastName="Jobs"},

            new Person(){ FirstName="Bill", LastName="Gates"},

            new Person(){ FirstName="Lary", LastName="Page"}

        };

        var str = String.Join(",", people.Select(p => p.FirstName) );

        Console.WriteLine(str);

    }

}

​

class Person

{

    public int Id { get; set; }

    public string FirstName { get; set; }

    public string LastName { get; set; }

}