Task: Validate International Securities Identification Number

C: #include <stdio.h>

int check_isin(char *a) {
    int i, j, k, v, s[24];
    
    j = 0;
    for(i = 0; i < 12; i++) {
        k = a[i];
        if(k >= '0' && k <= '9') {
            if(i < 2) return 0;
            s[j++] = k - '0';
        } else if(k >= 'A' && k <= 'Z') {
            if(i == 11) return 0;
            k -= 'A' - 10;
            s[j++] = k / 10;
            s[j++] = k % 10;
        } else {
            return 0;
        }
    }
    
    if(a[i]) return 0;
    
    v = 0;
    for(i = j - 2; i >= 0; i -= 2) {
        k = 2 * s[i];
        v += k > 9 ? k - 9 : k;
    }
    
    for(i = j - 1; i >= 0; i -= 2) {
        v += s[i];
    }
    
    return v % 10 == 0;
}

int main() {
    char *test[7] = {"US0378331005", "US0373831005", "U50378331005",
                     "US03378331005", "AU0000XVGZA3", "AU0000VXGZA3",
                     "FR0000988040"};
    int i;
    for(i = 0; i < 7; i++) printf("%c%c", check_isin(test[i]) ? 'T' : 'F', i == 6 ? '\n' : ' ');
    return 0;
}













Ada: procedure ISIN is
   
   function Luhn_Test (Number: String) return Boolean is
      Sum  : Natural := 0;
      Odd  : Boolean := True;
      Digit: Natural range 0 .. 9;
   begin
      for p in reverse Number'Range loop
         Digit := Integer'Value (Number (p..p));
         if Odd then
            Sum := Sum + Digit;
         else
            Sum := Sum + (Digit*2 mod 10) + (Digit / 5);
         end if;
         Odd := not Odd;
      end loop;
      return (Sum mod 10) = 0;
   end Luhn_Test;
   
   subtype Decimal   is Character range '0' .. '9';
   subtype Letter    is Character range 'A' .. 'Z';
   subtype ISIN_Type is String(1..12);
   
   
   function To_Digits(S: String) return String is
      
      Offset: constant Integer := Character'Pos('A')-10;
   
      Invalid_Character: exception;
   begin
      if S = "" then
         return "";
      elsif S(S'First) = ' ' then 
         return To_Digits(S(S'First+1 .. S'Last)); 
      elsif S(S'First) in Decimal then 
         return S(S'First) & To_Digits(S(S'First+1 .. S'Last));
      elsif S(S'First) in Letter then
         return To_Digits(Integer'Image(Character'Pos(S(S'First))-Offset))
           & To_Digits(S(S'First+1 .. S'Last));
      else 
         raise Invalid_Character;
      end if;
   end To_Digits;
   
   function Is_Valid_ISIN(S: ISIN_Type) return Boolean is
      Number : String := To_Digits(S);
   begin
      return S(S'First)   in Letter  and
             S(S'First+1) in Letter  and
             S(S'Last)    in Decimal and
             Luhn_Test(Number);
   end Is_Valid_ISIN;

   Test_Cases : constant Array(1..6) of ISIN_Type :=
      ("US0378331005",
       "US0373831005",
       "U50378331005",
       
       
       "AU0000XVGZA3",
       "AU0000VXGZA3",
       "FR0000988040");
begin
   for I in Test_Cases'Range loop
      Ada.Text_IO.Put_Line(Test_Cases(I) & ":" &
        Boolean'Image(Is_Valid_ISIN(Test_Cases(I))));
   end loop;
   
   Ada.Text_IO.Put("US03378331005:");
   Ada.Text_IO.Put_Line(Boolean'Image(Is_Valid_Isin("US03378331005")));
exception
   when others =>
      Ada.Text_IO.Put_Line("Exception occured");
end ISIN;