error 10327 please help! - error 10327 please help! I am trying to learn vhdl case statements and have been scratching my head trying to find the issue please help: library ieee; use ieee.std_logic_1164.all;library ieee; use ieee.std_logic_1164.all; use ieee.numeric_std.all; entity task1sq is port(a,b,c,d: in std_logic; sq: out std_logic); end task1sq; architecture behaviour of task1sq is begin process(a,b,c,d) --if implementation for prime begin case a & b & c & d is when "0011" => sq <= '0'; when "0010" => sq <= '0'; when "0101" => sq <= '0'; when "0111" => sq <= '0'; when "0110" => sq <= '0'; when "1100" => sq <= '0'; when "1101" => sq <= '0'; when "1111" => sq <= '0'; when "1110" => sq <= '0'; when "1000" => sq <= '0'; when "1011" => sq <= '0'; when "1010" => sq <= '0'; when others => sq <= '1'; end case; end process; end behaviour; Replies: Re: error 10327 please help! Thank you for acknowledge the solution provided. I’m glad that your question has been addressed, I now transition this thread to community support. Thank you. Best Regards, Richard Tan p/s: If any answer from the community or Intel Support are helpful, please feel free to give best answer or rate 4/5 survey. Replies: Re: error 10327 please help! The Error messages shown is: Error (10327): VHDL error at task1sq.vhd(15): can't determine definition of operator ""&"" -- found 4 possible definitions I have change the code below to pass the Analysis & Synthesis. Recommend to checkout this page https://nandland.com/case-statement/ on how to use the case statement. library ieee; use ieee.std_logic_1164.all;library ieee; use ieee.std_logic_1164.all; use ieee.numeric_std.all; entity task1sq is port(a,b,c,d: in std_logic; sq: out std_logic); end task1sq; architecture behaviour of task1sq is begin process(a,b,c,d) --if implementation for prime variable v_CONCATENATE : std_logic_vector(3 downto 0); begin v_CONCATENATE := a & b &c & d; case v_CONCATENATE is when "0011" => sq <= '0'; when "0010" => sq <= '0'; when "0101" => sq <= '0'; when "0111" => sq <= '0'; when "0110" => sq <= '0'; when "1100" => sq <= '0'; when "1101" => sq <= '0'; when "1111" => sq <= '0'; when "1110" => sq <= '0'; when "1000" => sq <= '0'; when "1011" => sq <= '0'; when "1010" => sq <= '0'; when others => sq <= '1'; end case; end process; end behaviour; Best Regards, Richard Tan p/s: If any answer from the community or Intel Support are helpful, please feel free to give best answer or rate 4/5 survey. Replies: Re: error 10327 please help! FYI it helps if you post the actual error message you get instead of just a number since that gives way more info, including what line number is causing the error. I googled and found this is an undefined operator error but I still don't know what line has the issue. My guess is that you need to have "end entity task1sq;" instead of just "end task1sq;".