Создание калькулятора на Lazarus

unit Unit1;
 
{$mode objfpc}{$H+}
 
interface
 
uses
  Classes, SysUtils, FileUtil, Forms, Controls, Graphics, Dialogs, StdCtrls,
  Buttons;
 
type
 
  { TForm1 }
 
  TForm1 = class(TForm)
    BitBtn1: TBitBtn;
    BitBtn2: TBitBtn;
    BitBtn3: TBitBtn;
    Button1: TButton;
    Button10: TButton;
    Button11: TButton;
    Button13: TButton;
    Button14: TButton;
    Button15: TButton;
    Button16: TButton;
    Button17: TButton;
    Button18: TButton;
    Button19: TButton;
    Button2: TButton;
    Button20: TButton;
    Button21: TButton;
    Button3: TButton;
    Button4: TButton;
    Button5: TButton;
    Button6: TButton;
    Button7: TButton;
    Button8: TButton;
    Button9: TButton;
    Edit1: TEdit;
    procedure BitBtn1Click(Sender: TObject);
    procedure BitBtn2Click(Sender: TObject);
    procedure BitBtn3Click(Sender: TObject);
    procedure Button11Click(Sender: TObject);
    procedure Button18Click(Sender: TObject);
    procedure Button19Click(Sender: TObject);
    procedure Button1Click(Sender: TObject);
    procedure Button20Click(Sender: TObject);
    procedure Button21Click(Sender: TObject);
    procedure ClickButton(Sender: TObject);
    procedure FormCreate(Sender: TObject);
    procedure ClickZnak(Sender: TObject);
  private
    { private declarations }
  public
    { public declarations }
  end;
 
var
    a,b,c:real;
    znak:string;
  Form1: TForm1;
 
implementation
 
{$R *.lfm}
 
{ TForm1 }
 
 
procedure TForm1.ClickZnak(Sender: TObject);
begin
  a:= StrToFloat(Edit1.Text);
  Edit1.Clear;
  znak:=(Sender as TButton).Caption;
 
 
end;
 
procedure TForm1.BitBtn1Click(Sender: TObject);
  var
      i:string;
begin
 i:= Edit1.text;
 if i <>'' then
 delete(i, Length(i),1);
 Edit1.Text:=i;
 
end;
 
procedure TForm1.BitBtn2Click(Sender: TObject);
begin
 a:= StrToFloat(Edit1.Text);
 a:=-(a);
 Edit1.Text:=FloatToStr(a);
end;
 
procedure TForm1.BitBtn3Click(Sender: TObject);
begin
 a:= StrToFloat(Edit1.Text);
 a:=sqrt(a);
 Edit1.Text:=FloatToStr(a);
end;
 
procedure TForm1.Button11Click(Sender: TObject);
begin
  Edit1.Text:=Edit1.Text + (Sender as TButton).Caption;
end;
 
procedure TForm1.Button18Click(Sender: TObject);
begin
  Edit1.Clear;
end;
 
procedure TForm1.Button19Click(Sender: TObject);
begin
  a:= StrToFloat(Edit1.Text);
 a:=(a*(a/100));
 Edit1.Text:=FloatToStr(a);
end;
 
procedure TForm1.Button1Click(Sender: TObject);
begin
 Edit1.Clear;
 a:=0;
 b:=0;
 c:=0;
end;
 
procedure TForm1.Button20Click(Sender: TObject);
begin
 a:= StrToFloat(Edit1.Text);
 a:=1/(a);
 Edit1.Text:=FloatToStr(a);
end;
 
procedure TForm1.Button21Click(Sender: TObject);
begin
  b:= StrToFloat (Edit1.Text);
  Edit1.Clear;
  case znak of
  '+': c:=a+b;
  '-': c:=a-b;
  '*': c:=a*b;
  '/': c:=a/b;
  end;
  Edit1.Text:=FloatToStr(c);
end;
 
procedure TForm1.ClickButton(Sender: TObject);
begin
  Edit1.Text:=Edit1.Text + (Sender as TButton).Caption;
end;
 
procedure TForm1.FormCreate(Sender: TObject);
begin
 
end;
 
end.

procedure TForm1.Button11Click(Sender: TObject);
begin
  Edit1.Text:=Edit1.Text + (Sender as TButton).Caption;
  if edit1.Text='00' then edit1.Text:='0';
end;

if edit1.Text='00' then edit1.Text:='0'
else Edit1.Text:=Edit1.Text + (Sender as TButton).Caption;

if Edit1.Text = '0' then Edit1.Text := (Sender as TButton).Caption else Edit1.Text:=Edit1.Text + (Sender as TButton).Caption;

procedure TForm1.Button11Click(Sender: TObject);
begin
 if pos(',',Edit1.Text)=0 then Edit1.Text:=Edit1.Text + (Sender as TButton).Caption;
end;