I Have imported the correct libraries and still get an error.

So i have this little piece of a datapath entity.

library ieee;

use ieee.std_logic_1164.all;

use IEEE.std_logic_arith.all;

use IEEE.std_logic_unsigned.all;

entity Datapath is port (

R1, R2, E1, E2, E3, E4, E5: in std_logic;

CLOCK_50: in std_logic;

SEQIN,SQR: in std_logic_vector (9 downto 0);

SW_erro, end_game, end_time, end_round: out std_logic;

Smt: out std_logic_vector(3 downto 0);

SmN: out std_logic_vector (3 downto 0);

result: out std_logic_vector (7 downto 0)

);

end Datapath;

architecture arqdtp of Datapath is

signal SmSwitches: std_logic_vector(2 downto 0);

signal SeqRom, SeqSw: std_logic_vector(9 downto 0);

signal SmT_in, SmN_in: std_logic_vector(3 downto 0);

signal C: std_logic;

begin

-- Registrador e Somador:

P1: process(CLOCK_50,R1)

begin

if (R1 = '1') then -- R1 Time reset

Smt_in<= "0101";

elsif (CLOCK_50'event AND CLOCK_50 = '1') then

if (E1 = '1') then

Smt_in <= Smt_in - '1';

SmT <= SmT_in;

end if;

end if;

end process;

P2: process(CLOCK_50,R2)

begin

if (R2 = '1') then -- R2 reset Next round

SmN_in<= "0000"; -- Soma Next round

elsif (CLOCK_50'event AND CLOCK_50 = '1') then

if (E3 = '1') then

SmN_in <= SmN_in + '1';

SmN <= SmN_in;

end if;

end if;

end process;

-- Comparador:

end_time <= '1' when (Smt_in = "0000") else '0';

end_round <= '1' when (SmN_in = "1010") else '0';

end_game <= '1' when (SeqSw = SeqRom)else '0';

SmSwitches <= (SEQIN(1)+SEQIN(2)+SEQIN(3)+SEQIN(4)+SEQIN(5)+SEQIN(6)+SEQIN(7)+SEQIN(8)+SEQIN(9)); -- For some reason it gives me the error here.

SW_erro<= '1' when (SmSwitches > "0100") else '0';

-- Sequencia secreta

P3: process(CLOCK_50,E4)

begin

if (E4 = '1') then -- Sequencia do Jogo reset

SeqSw<= "0000000000"; -- Sequencia 4 bits

elsif (CLOCK_50'event AND CLOCK_50 = '1' and E2 = '1') then

SeqRom <= SEQR;

end if;

end process;

-- Sequencia escolhida

P4: process(E5)

begin

if (E5 = '1') then -- Sequencia Escolhida reset

SeqRom<= "0000000000"; -- Sequencia 10 bits

C <= end_game;

result <= ("16" * C) + ("10" - SmN);

end if;

end process;

end arqdtp;

and i am still getting: Error (10327): VHDL error at Datapath.vhd(53): can't determine definition of operator ""+"" -- found 0 possible definitions

Can anyone please help me? It is urgent.