gistfile1.cs

/*first: you need to add the following to the head of your file to link with Windows library.*/
using Microsoft.Win32;

/* second you'll nedd to make a new object of the folder of current user registery */
RegistryKey rkApp = Registry.CurrentUser.OpenSubKey("SOFTWARE\\Microsoft\\Windows\\CurrentVersion\\Run", true);

/* third you have to add your application key : name and path */
rkApp.SetValue("HappyV", Application.ExecutablePath.ToString());

/* that line is to remove your application from the registery */
rkApp.DeleteValue("HappyV", false);