unit Unit1;

interface

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

type
  TForm1 = class(TForm)
    Edit1: TEdit;
    Button1: TButton;
    procedure Button1Click(Sender: TObject);
    procedure FormCreate(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
  end;

var
  Form1: TForm1;

implementation

{$R *.dfm}

procedure TForm1.Button1Click(Sender: TObject);
var c:char; s:string; a:integer;
begin
s:='BCDEFGHIKLMNOPQRSTVXYZ';
a:=a+1;
c:=s[a];
if Edit1.Text='' then
Edit1.Text:='A'
else
Edit1.Text:=Edit1.Text+c;
end;

procedure TForm1.FormCreate(Sender: TObject);
var a:integer;
begin
a:=0;
end;

end.