Building a directory string from component parts in C#

string CombinePaths(params string[] parts) {
    string result = String.Empty;
    foreach (string s in parts) {
        result = Path.Combine(result, s);
    }
    return result;
}

string CombinePaths(params string[] parts) {
    string result = String.Empty;
    foreach (string s in parts) {
        result = Path.Combine(result, s);
    }
    return result;
}

string CombinePaths(params string[] parts) {
    string result = String.Empty;
    foreach (string s in parts) {
        result = Path.Combine(result, s);
    }
    return result;
}

string[] ary = new string[] { "c:\", "Windows", "System" };
string path = ary.Aggregate((aggregation, val) => Path.Combine(aggregation, val));
Console.WriteLine(path); //outputs c:WindowsSystem

public static DirectoryInfo Subdirectory(this DirectoryInfo self, params string[] subdirectoryName)
    {
        Array.ForEach(
            subdirectoryName,
            sn => self = new DirectoryInfo(Path.Combine(self.FullName, sn))
            );
        return self;
    }

DirectoryInfo di = new DirectoryInfo("C:\")
            .Subdirectory("Windows")
            .Subdirectory("System32");

        DirectoryInfo di2 = new DirectoryInfo("C:\")
            .Subdirectory("Windows", "System32");

public static string CreateDirectoryName(string fileName, params string[] folders)
{
    if(folders == null || folders.Length <= 0)
    {
        return fileName;
    }

    string directory = string.Empty;
    foreach(string folder in folders)
    {
        directory = System.IO.Path.Combine(directory, folder);
    }
    directory = System.IO.Path.Combine(directory, fileName);

    return directory;
}