Reading xmlnode child tag value

My xml file looks like below.

<mappings>
  <mapping>
    <a>a1value</a>
    <b>
      <c>
        <d>d1value</d>
        <e>e1value</e>
      </c>
    </b>
  </mapping>
  <mapping>
    <a>a2value</a>
    <b>
      <c>
        <d>d2value</d>
        <e>e2value</e>
      </c>
    </b>
  </mapping>
</mappings>

C# code to read the value of a,d tags.

XmlDocument xmlDocNew = new XmlDocument();
XmlElement CATLOG = xmlDocNew.CreateElement("mappings");
XmlNode xmlNodeTab = xmltest.DocumentElement;
XmlNodeList xmlNodeListCD = xmlNodeTab.SelectNodes("//mapping");
foreach (XmlNode xmlNodeCD in xmlNodeListCD)
{
   string innerText = xmlNodeCD["a"].InnerText;
   string xmlNodeapp = xmlNodeCD["//b/c/d"].InnerText;
}

With the above code i am able to iterate through all the "a" tag elements.
But I am not able to read "d" tag value.
How do I read the value of "d" tag?

When I iterate through each element in the foreach loop, I want to get the value of "a" tag and its corresponding "d" tag value.

This code looks at each of the mapping and under it, looks up the value for tags a and d. Also note that if you want to look up 'sub' tags and only get these child items, you have to use .// instead of just //. Dot notation pulls node "under" the current node.

    XmlDocument doc = new XmlDocument();
    doc.Load($@"{Directory.GetParent(Environment.CurrentDirectory).Parent.Parent.FullName}\json.txt");

    var nodes = doc.SelectNodes("//mapping");
    foreach (XmlNode node in nodes)
    {
        var aNodes = node.SelectNodes(".//a");
        foreach (XmlNode aNode in aNodes)
            Console.WriteLine(aNode.InnerText);

        // If you know there will only be one node at .//b/c/d, use SelectSingleNode instead.
        Console.WriteLine(node.SelectSingleNode(".//b/c/d").InnerText);
    }

Output

a1value
d1value
a2value
d2value

Note:

a tag is sort of a sibling of d tag and their singular parent is the mapping element. You would get best results if you got all the mapping nodes and then worked through those.

Since .Net 3.5 there is Linq and Linq To XML which makes XML parsing easier. With Linq To XML you could read it as:

    void Main()
    {
    	var s = @"<mappings>
      <mapping>
        <a>a1value</a>
        <b>
          <c>
            <d>d1value</d>
            <e>e1value</e>
          </c>
        </b>
      </mapping>
      <mapping>
        <a>a2value</a>
        <b>
          <c>
            <d>d2value</d>
            <e>e2value</e>
          </c>
        </b>
      </mapping>
    </mappings>";
    	var data = from x in XDocument.Parse(s).Descendants("mapping")
    			   select new {
    			   	a=(string)x.Element("a"),
    				d=(string)x.Element("b").Element("c").Element("d")
    				};
    	
    	foreach (var e in data)
    	{
    		Console.WriteLine($"{e.a}, {e.d}");
    	}
    }

With a file, instead of .Parse, you would use .Load( filename ).

Output:

a1value, d1value
a2value, d2value

If you have a class matching this structure, like:

public class MyData
{ 
	public string A { get; set; }
	public string D { get; set; }
}

Then instead of the anonymous type you could use this class like so:

var data = from x in XDocument.Parse(s).Descendants("mapping")
		   select new MyData {
		   	A=(string)x.Element("a"),
			D=(string)x.Element("b").Element("c").Element("d")
			};

foreach (var e in data)
{
	Console.WriteLine($"{e.A}, {e.D}");
}

PS: Since you are getting an IEnumerable, you could directly bind data to a DataGridView, ListBox ... ( ...DataSource = data.ToList()).