architecture behavioral of addern is    signal result: unsigned (n+1 downto 1);    signal carry: unsigned(n+1 downto 1);    constant zeros: unsigned(n downto 1):=(others=>'0');        begin        carry<=(zeros&cin);        result<=('0'&unsigned(a))+('0'&unsigned(b))+carry;        sum<=std_logic_vector(result(n downto 1));        cout<=result(n+1);end behavioral;