Re: When using the Ada Big_Numbers.Big_Integers package, can the To_String function output be sliced?

[Kenneth Wolcott <kennethwolcott@gmail.com>]

On Saturday, July 29, 2023 at 4:49:08 PM UTC-7, Kenneth Wolcott wrote:
> On Saturday, July 29, 2023 at 4:07:17 AM UTC-7, AdaMagica wrote: 
> > > Powers_of_2 := Powers_of_2 * To_Big_Integer (2); 
> > With the aspect Integer_Literal, also Powers_of_2 * 2 must work. The attributes Integer_Literal, Real_Literal, Put_Image make the new big numbers nearly work like numeric types (they are not). A difference: The range syntax for instance in loops A .. B is illegal.
> I understand that the range syntax in loops implies that the loop variable is acting like an enumerated type which is not true for Big_Integers. 
> 
> What confused me is that I thought I had to convert the numeric literal (I'll have to go back and look at the package spec again to get this firmly understood. 
> 
> I have an another question about string slicing: I've tried (obviously incorrectly) to use a variable is one of the slice integers. Can this be done? 
> 
> Thanks, 
> Ken

Apparently not :-(

gnatmake main.adb
gcc -c main.adb
main.adb:28:67: error: named parameters not permitted for attributes
     9	with Ada.Text_IO; use Ada.Text_IO;
    10	with Ada.Integer_Text_IO; use Ada.Integer_Text_IO;
    11	with Ada.Float_Text_IO; use Ada.Float_Text_IO;
    12	with Ada.Numerics.Elementary_Functions; use Ada.Numerics.Elementary_Functions;
    13	with Ada.Command_Line; use Ada.Command_Line;
    14
    15	procedure Main is
    16	  Substr : String := Argument (1);
    17	  Nth : Positive := Integer'Value (Argument (2));
    18	  I, J : Natural;
    19	  Temp : Float;
    20	begin
    21	  I := 0;
    22	  J := 0;
    23	  loop
    24	    I := I + 1;
    25	    exit when I >= 10;
    26	    Temp := 10.0 ** (log (2.0, 10.0) * Float (I));
    27	    if I >= 4  then
    28	      if (Float'Image (10.0 ** (log (2.0, 10.0) * Float (I)), Aft => 0, Exp => 0) (1 .. Substr'Length) = Substr then
    29	        J := J + 1;
    30	        if J = Nth then
    31	          Put (I, 0);
    32	          New_Line;
    33	          exit;
    34	        end if;
    35	      end if;
    36	    end if;
    37	  end loop;
    38	end Main;

Thanks,
Ken