Visual Basic - Apis para cerrar aplicaciones

Deseo saber la manera de cerrar ventanas activas dentro del windows, sin cerrar aplicaciones residentes en memoria

Declare Function FindWindow Lib \"user32\" Alias \"FindWindowA\" (ByVal lpClassName As String, ByVal lpWindowName As String) As Long

Declare Function SendMessage Lib \"user32\" Alias \"SendMessageA\" (ByVal hWnd As Long, ByVal wMsg As Long, ByVal wParam As Long, lParam As Any) As Long

Public Const WM_CLOSE = &H10
Public Const NILL = 0&
Public Const WM_SYSCOMMAND = &H112
\' Primero activá la Calculadora

Private Sub Command1_Click()
HWH=Findwindows(0&,\"Calculadora\")
If HWH <> 0 then
SendMessage HWH, WM_SYSCOMMAND, SC_CLOSE, NILL

Else
msgbox \" No está activa la Calculadora\"
EndIf

end Sub

Hay una manera más sencilla a mi modo de ver:

Private Declare Function PostMessage Lib "user32" Alias "PostMessageA" (ByVal hwnd As Long, ByVal wMsg As Long, ByVal wParam As Long, lParam As Any) As Long
Const WM_CLOSE = &H10

PostMessage WinWnd, WM_CLOSE, 0&, 0&

Sólo tienes que pasarle el manejador de la ventana que lo puedes obtener facilmente con el API FindWindow, y listo.
Saludos