Zap all files from all subdirectories recursively

zapall.cs

using System.IO;

namespace ZapAll
{
    class Program
    {
        private static readonly char separator = Path.DirectorySeparatorChar;

        static void Main(string[] args)
        {
            foreach (var item in Directory.EnumerateDirectories(Directory.GetCurrentDirectory()))
            {
                Zap(item);
            }
        }

        static void Zap(string path)
        {
            // process children directories first
            foreach (var dir in Directory.EnumerateDirectories(path))
            {
                Zap(dir);
            }

            // zap all files
            foreach (var oldPath in Directory.EnumerateFiles(path))
            {
                var newPath = oldPath.Insert(oldPath.LastIndexOf(separator), "_");
                newPath = newPath.Remove(newPath.LastIndexOf(separator), 1);

                File.Move(oldPath, newPath);
            }

            // delete directory
            Directory.Delete(path);
        }
    }
}