Converting Binary to Decimal

["WM" <wwminirl@hotmail.com>]

I am writing a program like this:
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with Ada.Text_Io,Ada.Integer_Text_Io;
use Ada.Text_Io,Ada.Integer_Text_Io;

procedure Bin_2_Dec_Test is

   answer : integer;
   subtype Binary_Number is Integer range 0..1; --define data type
   type a_bin_num is array(1..8) of Binary_Number; --define array type

   bin : Binary_Number;

   function Bin_To_Dec(bin:Binary_Number) return Integer is
      Answer : Integer :=0;
   begin
      for J in reverse 1..8 loop
         Answer := Answer + a_bin_num(Bin(J))*(2**(J-1));
      end loop;
      return Answer;
   end Bin_To_Dec;

begin
   Put_Line("input binary number please: ");
   for num in 1..8 loop
      Get(a_bin_num(num));
   end loop;
   Put_Line("decimal is: ");
   Put(Answer(a_bin_num));
end Bin_2_Dec_Test;
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It gives me a lot of errors... really don't know what's wrong...
Please give some hints, thanks!