unit Unit1;

interface

uses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs, StdCtrls;

type
  TForm1 = class(TForm)
    Button1: TButton;
    Button2: TButton;
    procedure Button1Click(Sender: TObject);
    procedure Button2Click(Sender: TObject);
  end;

var
  Form1: TForm1;

implementation

{$R *.dfm}

//TStringBuilder.CopyTo
procedure TForm1.Button1Click(Sender: TObject);
var
  sb: TStringBuilder;
  arr: TCharArray;
  i: Integer;
begin
  sb := TStringBuilder.Create;
  sb.Append('123456789');

  SetLength(arr, 9);
  for i := Low(arr) to High(arr) do arr[i] := '*';

  sb.CopyTo(3, arr, 1, 5);
  ShowMessage(PChar(arr));   {*45678***}

  sb.Free;
end;

//TStringBuilder.Chars
procedure TForm1.Button2Click(Sender: TObject);
var
  sb: TStringBuilder;
begin
  sb := TStringBuilder.Create('Delphi 2009');

  ShowMessage(sb.Chars[0]);             {D}
  ShowMessage(sb.Chars[sb.Length - 1]); {9}

  sb.Free;
end;

end.