using System;

using System.Xml;

using System.Linq;

using System.Xml.Linq;

using System.Collections.Generic;

public class Program

{

    public static void Main()

    {

        //var xDoc = XDocument.Load(filename);

        var XDoc = XDocument.Parse(@"<root><a><b><c>value</c></b></a><b><c>no</c></b><a><c>no</c></a></root>");

        Console.WriteLine("Params a b c ");

        foreach(var nodeValue in XDoc.Root.GetValueForNodeIfExists("a", "b", "c"))

        {

            Console.WriteLine(nodeValue);

        }

        Console.WriteLine("List a b c ");

        foreach(var nodeValue in XDoc.Root.GetValueForNodeIfExists("a", "b", "c"))

        {

            Console.WriteLine(nodeValue);

        }

    }

}   

​

​

internal static class XElementExtensions

{

    public static IEnumerable<string> GetValueForNodeIfExists(this XElement node, params string[] childNodesNames)

    {

        return GetValueForNodeIfExists(node, childNodesNames.ToList());

    }

​

    public static IEnumerable<string> GetValueForNodeIfExists(this XElement node, IEnumerable<string> childNodesNames)

    {

        IEnumerable<XElement> nodes = new List<XElement> { node };

        foreach(var name in childNodesNames)

        {

            nodes = FilterChildrenByName(nodes, name);

        }

        var result = nodes.Select(n => n.Value);

        return result;

    }

    private static IEnumerable<XElement> FilterChildrenByName(IEnumerable<XElement> nodes, string filterName)

    {

        var result = nodes

            .SelectMany(n => n.Elements(filterName));

        Console.WriteLine("Filtering by {0}, found {1} elements", filterName, result.Count());

        return result;          

    }

}