I m curently work out this converter but the compilation is not successful. Below is the codes and error message. And I am using shift add3 algorithm for this.

LIBRARY ieee;
USE ieee.STD_LOGIC_1164.all;
USE ieee.STD_LOGIC_ARITH.all;
USE ieee.STD_LOGIC_UNSIGNED.all;

ENTITY projectTest3 IS
port( D  : in std_logic_vector(15 downto 0);       
   Q  : out std_logic_vector(15 downto 0));
END projectTest3;
ARCHITECTURE behavioral OF projectTest3 IS
Begin  
 PROCESS(D)
 variable r: STD_LOGIC_VECTOR (15 DOWNTO 0);
  BEGIN
  r:=(others=>'0');
  r(4 DOWNTO 0):=D(15 DOWNTO 11);
  FOR i IN 0 TO 9 loop
      IF D(10-i)='1' then
   r(5+i DOWNTO 0) := r(4+i DOWNTO 0) & '1';
   ELSE
   r(4+(i+1) DOWNTO 0) := r(4+i DOWNTO 0) & '0';
   END IF;
   
   IF r(3 DOWNTO 0) >= 5 then
    r(3 DOWNTO 0) := r(3 DOWNTO 0) + "0011";
    IF r(7 DOWNTO 4) >= 5 then
     r(7 DOWNTO 4) := r(7 DOWNTO 4) + "0011";
     IF r(11 DOWNTO 8) >= 5 then
      r(11 DOWNTO 8) := r(11 DOWNTO 8) + "0011";
     END IF;
    END IF;
   END IF;
  END LOOP;
  Q(15 downto 0) <= r(15 downto 0);
 END PROCESS;
end behavioral;


Error:  a deferred constant declaration without a full declaration is not supported
ANYone can help?
THANKs in advance

Hi,
I think you have recently used the VHDL. Remember that VHDL is   the language to design the hardware but not the software. Your program seems to be used for C language in computer. I think the trouble is here :
  FOR i IN 0 TO 9 loop
      IF D(10-i)='1' then
          r(5+i DOWNTO 0) := r(4+i DOWNTO 0) & '1';
      ELSE
          r(4+(i+1) DOWNTO 0) := r(4+i DOWNTO 0) & '0';
      END IF

The compiler cannot generate the hardware  to do this. So tell me what your program need to do in detail. I will give you some suggestion.

Yes. I'm new to VHDL. Actually i am designing a calculator tht can perform addition, subtraction and multiplication only. User will key in the maximum 2 BCD numbers (56+72, 56*4,...).For addition and subtraction, i can do it in BCD. But for multiplication, I have to convert bcd into binary code then the binary result has to convert it back into bcd. I have stucked in the binary to bcd conversion. Hope u can help me... Thanks in advance.

Hi,
You can see more informations in this link : http://www.tek-tips.com/viewthread.cfm?qid=840645

Or you can search in google with keyword "bcd to binary vhdl".
There are many examples or source code for reference.
Good luck.