For those who want to learn about windows, I leave the code I was looking for...

"Programatically filling a ComboBox and setting it visible or invisible"

HWND hWndComboBox[10];
    char numChar[20]; // String that contains a number converted to string
    int yPos = 160, xPos = 60;
    int counter1, counter2;    // 
        case WM_INITDIALOG:
            for(counter1 = 0; counter1 < MAX_COMBOS; counter1++){
                hWndComboBox[counter1] = CreateWindow("COMBOBOX", NULL, WS_CHILD | [B]WS_VISIBLE[/B] | WS_TABSTOP | CBS_DROPDOWN | WS_VSCROLL, xPos, yPos, 60, 60, hWndDlg, NULL, hInst, NULL);
                    MessageBox(hWndDlg, "Could not create the combo box", "Failed Control Creation", MB_OK);
                    return FALSE;
                // I'll fill the ComboBoxes with numbers from 1 to LAST_NUMBER
                for(counter2 = 1; counter2 <= LAST_NUMBER; counter2 ++){
                    itoa(counter2 , numChar, 10);
                    SendMessage(hWndComboBox[counter1], CB_ADDSTRING, 0, reinterpret_cast<LPARAM>((LPCTSTR)numChar));
            return TRUE;

I would like to thank the ones who "made the effort to answer me"... even if it was only to tell me that they didn't know how to do it

"Sometimes is better to say I don't know..."

you might submit this in the C code snippets board :)