private void BtnAddRemove_Click(object sender, EventArgs e)
        {
            //to have access to HKEY_LOCAL_MACHINE and if u need to add only for HKEY_CURRENT_USER, 
            //use CurrentUser instead of LocalMachine
            RegistryKey rk = Registry.LocalMachine;
            RegistryKey mykey;

            //access the regitry key where you want to add your registry key
            mykey= rk.OpenSubKey(@"Software\Microsoft\Windows\CurrentVersion\Run", true);
            if (chkAddRemove.Checked == true )
            {
                //check if same registry value exists or not ......and create only if it is not there 
                if (mykey.GetValue("myApp") == null)
                {
                    mykey.SetValue("myApp", Application.ExecutablePath, RegistryValueKind.ExpandString);
                }

                    //dislpay message box if registry is already there
                else
                {
                    MessageBox.Show("The entry already exists");
                }
            }

                //delete if the user has uncked the checkbox....and the value exists in the registry
            else
            {
                if (mykey.GetValue("myApp") != null)
                    mykey.DeleteValue("myApp");
            }
        }