Detecting if 'Control' or 'Shift' key was down when key pressed

[Icyculyr]

I have been looking into detecting key stuff, it works great, I am trying to figure out if control or shift was pressed, I read in some MSDN documentation (I use Visual C++), that lParam is 0 if ctrl or shift isn't down, or 1 if they are, but how do I tell which one?

I may be wrong, it had a table structure saying stuff like:

0-15 repeat count
16-18 reserved, do not use

19-23 = something

24 = if the right hand shift or control key is down on an extended 101-102 key keyboard.. returns 1 if it is, otherwise returns 0

My code for keys:

CASE WM_KEYDOWN:
    {
    if (LOWORD(lParam) == 1)
    {
        MessageBox(hWnd, _T("Ctrl Or Shift down"), _T("CAP"), 0);
    }
    int iKey = LOWORD(wParam);
    if (iKey == 37) //LEFT ARROW
    {
        MessageBox(hWnd, _T("LA"), _T("CAP"), 0);
    }
    else if (iKey == 39) //RIGHT ARROW
    {
        MessageBox(hWnd, _T("RA"), _T("CAP"), 0);
    }
    }

I get the message Ctrl Or Shift down, when I hold either of them down, but I don't if I don't hold them down...

How do I tell which one was pressed? Thanks