unit Unit1;
interface
uses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs, StdCtrls;
type
  TForm1 = class(TForm)
    Edit1: TEdit;
    Edit2: TEdit;
    Edit3: TEdit;
    Edit4: TEdit;
    Edit5: TEdit;
    btnPlus: TButton;
    btnMinus: TButton;
    procedure FormCreate(Sender: TObject);
    procedure btnPlusClick(Sender: TObject);
    procedure btnMinusClick(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
  end;

var
  Form1: TForm1;
  EditSet : array of TEdit ;
  idx: integer;
implementation

{$R *.dfm}
procedure TForm1.FormCreate(Sender: TObject);
begin
  //set edit1..edit5 invisible;
  idx := 0;
  EditSet[1] := Edit1;
  EditSet[2] := Edit2;
  EditSet[3] := Edit3;
  EditSet[4] := Edit4;
  EditSet[5] := Edit5;
end;
procedure TForm1.btnPlusClick(Sender: TObject);
begin
  inc(idx);
  if idx > 5 then
  begin
    idx := 6;
    exit;
  end;
  EditSet[idx].Visible := true;
end;
procedure TForm1.btnMinusClick(Sender: TObject);
begin
  dec(idx);
  if idx < 1 then
  begin
    idx := 0;
    exit;
  end;
  EditSet[idx].Visible := false;
end;
end.