using System;

using System.IO;

using System.Collections.Generic;

using System.Linq;

using System.Globalization;

using System.Xml.Linq;

public class Program

{

​

    public static void Main()

    {

        string input = @"<People>

<Person name=""John"" />

<Person name=""Andrew"" />

</People>";

            XDocument doc = XDocument.Parse(input);

​

            var isJohnHere = doc.Element("People")

                                .Descendants("Person")

                                .Any(x=> x.Attribute("name").Value == "John");

            var names = doc.Element("People")

                            .Descendants("Person")

                            .Select(x=> x.Attribute("name").Value);

    }

}