using System;

using System.Linq;

using System.Xml;

public class Program

{

    public static void Main()

    {

        string xml1 = "<test><ex1>1/1/2014</ex1></test>"; // Base case with ex1

        string xml2 = "<test></test>"; // No ex1

        string xml3 = "<test><ex1></ex1></test>"; // Empty tag

        var p = new Program();

        Console.WriteLine("1: {0}", p.GetValue(xml1, "N/A"));

        Console.WriteLine("2: {0}", p.GetValue(xml2, "N/A"));

        Console.WriteLine("3: {0}", p.GetValue(xml3, "N/A"));

    }

    public string GetValue(string xml, string defaultValue)

    {

        var xmlDoc = new XmlDocument();

        xmlDoc.LoadXml(xml);

        var node = xmlDoc.SelectSingleNode(".//ex1");

        return (node == null || string.IsNullOrEmpty((node.InnerText ?? "").Trim()) ? defaultValue : node.InnerText.Trim());

    }

}