FileListings.cs

using System.Collections;
using System.IO;

class FileListings {
  public void ListFiles() {
    var directory = new System.IO.DriveInfo(@"C:\").RootDirectory;

    var folders = new Stack<DirectoryInfo>();
    var files = new Stack<FileInfo>();

    folders.Push(directory);

    while (folders.Count != 0) {
      var poppedFolder = folders.Pop();
    
      if (poppedFolder.Exists) {
        var __folders = poppedFolder.GetDirectories();
        var __files = poppedFolder.GetFiles();

        // push all the folders into our folder list.
        foreach(var folder in __folders) {
          // push the new folder into our list of folders.
          folders.Push(folder);
        }
      
        // push all the files into our file list.
        foreach(var file in __files) {
          // push the file into our list of files.
          files.Push(file);
        }
      }
    }
  }
}