Traverse Windows Directories

namespace TraverseWindowsDirectories
{
    using System;
    using System.Collections.Generic;
    using System.IO;
    using System.Text;

    /// <summary>
    /// Write a program to traverse the directory C:\WINDOWS and all its subdirectories recursively and to display all files matching the mask *.exe. Use the class System.IO.Directory.
    /// </summary>
    public class TraverseWindowsDirectories
    {
        private static readonly List<string> files = new List<string>();

        public static void Main()
        {
            string rootDirectory = @"C:\Windows";
            string fileExtension = "*.exe";

            TraverseDirectory(rootDirectory, fileExtension);

            Console.WriteLine(PrintFiles(files));
        }

        private static void TraverseDirectory(string currentPath, string fileExtension)
        {
            string[] currentDirectoryFiles = Directory.GetFiles(currentPath, fileExtension);
            files.AddRange(currentDirectoryFiles);

            string[] currentDirectorySubDirectories = Directory.GetDirectories(currentPath);
            try
            {
                foreach (var directory in currentDirectorySubDirectories)
                {
                    TraverseDirectory(directory, fileExtension);
                }
            }
            catch (System.UnauthorizedAccessException excpt)
            {
                Console.WriteLine(excpt.Message);
            }
        }

        private static string PrintFiles(List<string> files)
        {
            StringBuilder output = new StringBuilder();

            for (int i = 0; i < files.Count; i++)
            {
                output.AppendLine(files[i]);
            }

            return output.ToString();
        }
    }
}