keyboard input with WM_CHAR

I want the window to be maximized when the user presses Alt+Enter. Here is the relevant piece of code:

Code:

---

case WM_CHAR:
    if (wParam == 0x0D && (HIWORD(lParam) & KF_ALTDOWN)) {
        SendMessage(hwnd, WM_SYSCOMMAND, SC_MAXIMIZE, 0);
    }
    break;

---

However, upon pressing Alt+Enter, nothing happens. Can someone explain why?