Reading an XML file then writing to a duplicate version

Question 1

If you want to use LINQ to XML for the purpose, then your code can look like this:

var input = @"d:\temp\in.xml";
var output = @"d:\temp\out.xml";

try
{          
    // load original file
    var xmlDocument = XDocument.Load(input);
    // don't forget to take the namespace, otherwise LINQ will not find the elements
    XNamespace ns = "http://schemas.microsoft.com/developer/msbuild/2003";
    // finder helper
    Func<string, IEnumerable<XElement>> getElements = elementName => 
        // find all elements of type ItemGroup
        // that contain elements of the given type (here ClInclude or ClCompile)
        xmlDocument.Root.Elements(ns + "ItemGroup").Elements(ns + elementName);
    // find elements: ClInclude
    var clInputs = getElements("ClInclude");
    foreach (var clInput in clInputs)
    {
        // fetch attribute
        var inputAttribute = clInput.Attributes("Include");
        // take first and modify it
        inputAttribute.ElementAt(0).Value = "some new value";
    }
    // find elements: ClCompile
    var clCompiles = getElements("ClCompile");
    foreach (var clCompile in clCompiles)
    {
        // fetch attribute
        var compileAttribute = clCompile.Attributes("Include");
        // take first and modify it
        compileAttribute.ElementAt(0).Value = "some other value";
    }
    // save modified file under new name
    xmlDocument.Save(output);
}
catch (Exception ex)
{
    Console.WriteLine(ex.Message);
}

The modified sections in the new output looks like this:

<ItemGroup>
    <ClCompile Include="some other value" />
    <ClCompile Include="some other value" />
    ...
    <ClCompile Include="some other value" />
</ItemGroup>
<ItemGroup>
    <ClInclude Include="some new value" />
    ...
    <ClInclude Include="some new value" />
</ItemGroup>

More information on LINQ to XML can be found at MSDN.

Question 2

Sorry, but why you can't use new STUFF which Microsoft recommend to use? I give you an example. Add

using System.IO;
using System.Xml.Linq;

Let's say you have a xml file

<?xml version="1.0" encoding="utf-8" ?> 
<Root>
    <Employee>
        <Name>
            John
        </Name>
        <Last>
            Smith
        </Last>
        <Email>
            js@gmail.com
        </Email>
    </Employee>
    <Employee>
        <Name>
            Danial
        </Name>
        <Last>
            Black
        </Last>
        <Email>
            db@gmail.com
        </Email>
    </Employee>
    <Employee>
        <Name>
            Marry
        </Name>
        <Last>
            Sweet
        </Last>
        <Email>
            ms@gmail.com
        </Email>
    </Employee>
</Root>

And you want to modify Name in each Employee

XDocument xDoc = XDocument.Load(@"C:\example.xml");

xDoc.Descendants(XName.Get("Employee")).ToList().ForEach(x =>
        {
            string name = x.Element(XName.Get("Name")).Value;   
            x.Element(XName.Get("Name")).Value = name + " Junior";

        });

xDoc.Save(@"C:\result.xml");

And that's all!

Question 3

Ok you just forgot Namespace

This example uses your xml

            XElement xElement = XElement.Load(@"C:\target.xml");
            string ns = xElement.Name.Namespace.NamespaceName;

            xElement.Descendants(XName.Get("ClCompile", ns)).ToList().ForEach(x =>
            {
                XAttribute xAttr =  x.Attribute(XName.Get("Include"));

                if (xAttr != null)
                {
                    string name = xAttr.Value;
                    xAttr.Value = name + "?modified";
                }

            });


            xElement.Descendants(XName.Get("ClInclude", ns)).ToList().ForEach(x =>
            {
                XAttribute xAttr = x.Attribute(XName.Get("Include"));

                if (xAttr != null)
                {
                    string name = xAttr.Value;
                    xAttr.Value = name + "?included";
                }
            });

            xElement.Save(@"C:\result.xml");

So I just add a string to the tags which have the Include attribute!