how to stop moving app edges when its tried to move outside the screen limits?

void CDemoDlg::OnLButtonDown(UINT nFlags, CPoint point)
{
	// TODO: Add your message handler code here and/or call default

	 CRect myRect;
	 GetWindowRect(&myRect);
              //save current cursor coordinate
		GetCursorPos(&point);
		//ScreenToClient(&point);
		SendMessage(WM_NCLBUTTONDOWN, HTCAPTION, 0);
	__super::OnLButtonDown(nFlags, point);
}
 
void CDemoDlg::OnMouseMove(UINT nFlags, CPoint point)
{
	// TODO: Add your message handler code here and/or call default

	CRect myRect;
	 GetWindowRect( &myRect);
	 CPoint curpoint;
	 GetCursorPos(&curpoint);
     {     
           MoveWindow(curpoint.x - point.x, curpoint.y - point.y, 
			myRect.right - myRect.left, myRect.bottom - myRect.top, TRUE);
     }
	
	 __super::OnMouseMove(nFlags, point);
}
void CDemoDlg::OnPaint() 
{
	if (IsIconic())
	{
		CPaintDC dc(this); // device context for painting

		SendMessage(WM_ICONERASEBKGND, (WPARAM) dc.GetSafeHdc(), 0);

		// Center icon in client rectangle
		int cxIcon = GetSystemMetrics(SM_CXICON);
		int cyIcon = GetSystemMetrics(SM_CYICON);
		CRect rect;
		GetClientRect(&rect);
		int x = (rect.Width() - cxIcon + 1) / 2;
		int y = (rect.Height() - cyIcon + 1) / 2;

		// Draw the icon
		dc.DrawIcon(x, y, m_hIcon);
	}
	else
	{
		
		CPaintDC dc(this);
		CRect rect;
		GetClientRect(&rect);
		//ScreenToClient(rect);
		BITMAP bmp;
		HBITMAP hBmp = ::LoadBitmap(::AfxGetInstanceHandle(), MAKEINTRESOURCE(IDB_MAIN_BG));
		::GetObject(hBmp, sizeof(bmp), &bmp);
		HDC hDC = ::CreateCompatibleDC(NULL);
		SelectObject(hDC, hBmp);
		::BitBlt(dc.m_hDC, 0, 0, rect.Width(), rect.Height(), hDC, 0, 0, SRCCOPY);
		CDialog::OnPaint();
	}

}