Probleme de selection dans une combobox

HWND hGroup=CreateWindow(
        TEXT("BUTTON"),
        TEXT("Premier paramètre"),
        WS_CHILD|WS_VISIBLE|BS_GROUPBOX,
        10,10,
        200,100,
        fenetrePrincipale,
        NULL,
        instance,
        NULL);
    {
        
		hComboBox1=CreateWindow(
        TEXT("COMBOBOX"),
        TEXT(""),
        WS_CHILD|WS_VISIBLE|CBS_DISABLENOSCROLL|CBS_DROPDOWNLIST,
        20,40,
        180,150,
        fenetrePrincipale,
        (HMENU)ID_COMBOBOX_1,
        instance,
        NULL);

		//Remplissage
		SendMessage(hComboBox1, CB_ADDSTRING, 0, (LONG)TEXT("plop"));
		SendMessage(hComboBox1, CB_ADDSTRING, 0, (LONG)TEXT("plop2"));
		SendMessage(hComboBox1, CB_ADDSTRING, 0, (LONG)TEXT("flop"));
		SendMessage(hComboBox1, CB_ADDSTRING, 0, (LONG)TEXT("tlop"));
		SendMessage(hComboBox1, CB_ADDSTRING, 0, (LONG)TEXT("plip"));
		
		
		
			
		combo1_2 = CreateWindow(TEXT("COMBOBOX"),
		TEXT(""), WS_CHILD|WS_VISIBLE|CBS_DISABLENOSCROLL|CBS_DROPDOWNLIST,
		20,80,150,200,
		fenetrePrincipale,
		0,
		instance, NULL);

	}

switch (mes)
   {
   case WM_CREATE:
		RemplieFenetrePrincipale(hWnd);		
		return 0;

   case WM_COMMAND:
		if(HIWORD(wParam)==CBN_SELENDOK)
		{
			element = SendMessage(hComboBox1, CB_GETCURSEL, 0,0);
			if (element < 3) {
				//Si on selectionne une chaine, un entier ou un bool on affiche l'edit box sinon on affiche la combo
				ShowWindow(editbox,SW_SHOW);	
				ShowWindow(combo1_2, SW_HIDE);
			}
			else {
				ShowWindow(combo1_2,SW_SHOW);
				ShowWindow(editbox, SW_HIDE);
			}
			//On récupére les valeur de la deuxieme combo
			Recup(bRet,MonString,RetTaille,hWnd,hComboBox1,combo1_2 );

[...suite du code]

if(HIWORD(wParam)==CBN_SELENDOK && (HWND)lParam==hComboBox1)
{
    //Traitement pour le premier combobox:
    element=....
    //...
    return 0;
}
if(HIWORD(wParam)==CBN_SELENDOK && (HWND)lParam==combo1_2)
{
    //Traitement pour le deuxième  combobox:
    //....
    return 0;
}

if(HIWORD(wParam)==ID_BUTTON_1)
{
    //Traitement
}