unit adt;

interface

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

type
  Tdataplay = class(TForm)
    collection: TLabel;
    Label1: TLabel;
    Label2: TLabel;
    data: TEdit;
    push: TButton;
    pop: TButton;
    enqueue: TButton;
    dequeue: TButton;
    done: TButton;
    t: TLabel;
    h: TLabel;
    procedure doneClick(Sender: TObject);
    procedure pushClick(Sender: TObject);
    procedure popClick(Sender: TObject);
    procedure enqueueClick(Sender: TObject);
    procedure update;
    procedure FormCreate(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
  end;

var
  dataplay: Tdataplay;

implementation

{$R *.DFM}

procedure TDataplay.update;
{change the values displayed as head and tail}
var long  : integer;
begin
  long := length(collection.caption);
  if long > 0
    then begin
           h.caption := collection.caption[long];
           t.caption := collection.caption[1]
         end
    else begin
           h.caption := '';
           t.caption := ''
         end
end;

procedure Tdataplay.doneClick(Sender: TObject);
begin
  close
end;

procedure Tdataplay.pushClick(Sender: TObject);
begin
  collection.caption := collection.caption + data.text[1];
  update
end;

procedure Tdataplay.popClick(Sender: TObject);
var  head       : integer;
     tempstring : string;
begin
  tempstring := collection.caption;  {get a copy of what is there}
  head       := length(tempstring);  {identify the position of the head of the stack}

  if head > 0   {the stack is not empty}
    then begin
            data.text  := tempstring[head];      {get the char at the head}
            delete(tempstring, head, 1);         {now remove that cha from the head}
            collection.caption := tempstring     {now refresh the displayed value}
         end
    else showmessage('There is no data left');
  update
end;

procedure Tdataplay.enqueueClick(Sender: TObject);
begin
  collection.caption := data.text[1] + collection.caption;
  update
end;

procedure Tdataplay.FormCreate(Sender: TObject);
begin
  update
end;

end.