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if Lenght(Edit1.Text < 4) then Edit1.Text := Edit1.Text + '1';                    

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if (length(edit1.text) = 4) then key := #7 else edit1.text := edit1.text + key;                    

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Procedure TMyForm.Button0Click (Sender : TObject);
Begin
  EditEingabe.Text := EditEingabe.Text + '0';
End;                    

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if Lenght(Edit1.Text < 4) then // Wenn bis jetzt weniger als 4 Zeichen im Edit1 sind, dann
  Edit1.Text := Edit1.Text + '1'; // der neue Text von Edit1 ist der alte plus die Zahl 1                    

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if Length(Edit1.Text) < 4 then // Wenn bis jetzt weniger als 4 Zeichen im Edit1 sind, dann
  Edit1.Text := Edit1.Text + '1'; // der neue Text von Edit1 ist der alte plus die Zahl 1                    

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procedure TForm1.Button1Click(Sender: TObject);
begin
  if Length(Edit1.Text)< 4 then Edit1.Text:=Edit1.Text + '1'
  else Button1.Enabled:= False;
end;

procedure TForm1.Button2Click(Sender: TObject);
begin
  if Length(Edit1.Text)< 4 then Edit1.Text:=Edit1.Text + '2'
  else Button2.Enabled:= False;
end;                    

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// der neue Text von Edit1 ist der alte mit dem aus einem Zeichen bestehenden String '1' angehängt                    

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unit hauptprogramm;

interface

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

type
  Tmainform = class(TForm)
    pin_edit: TEdit;
    Button1: TButton;
    Button2: TButton;
    Button3: TButton;
    Button4: TButton;
    Button5: TButton;
    Button6: TButton;
    Button7: TButton;
    Button8: TButton;
    Button9: TButton;
    Button10: TButton;

   procedure FillInNumber(Sender: TObject);
    procedure FormCreate(Sender: TObject);
  private
    { Private-Deklarationen }
  public
    { Public-Deklarationen }
  end;

var
  mainform: Tmainform;
  InAEdit: TEdit;

implementation

{$R *.dfm}

procedure Tmainform.FillInNumber(Sender: TObject);
begin;
 if length(InAEdit.Text) >= 4 then
  InAEdit.Clear;

 InAEdit.text:= InAEdit.text + TButton(Sender).Caption;
end;

procedure Tmainform.FormCreate(Sender: TObject);
begin
 InAEdit:= pin_edit;
end;

end.                    

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unit Unit1;

interface

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

type
  TForm1 = class(TForm)
    Panel1: TPanel;
    Button3: TButton;
    Button4: TButton;
    Button5: TButton;
    Button6: TButton;
    Button7: TButton;
    Button8: TButton;
    Button9: TButton;
    Button10: TButton;
    Button1: TButton;
    Button2: TButton;
    Edit1: TEdit;
    BitBtn1: TBitBtn;
    Label1: TLabel;
    Panel2: TPanel;
    procedure Button1Click(Sender: TObject);
    procedure Button2Click(Sender: TObject);
    procedure Button3Click(Sender: TObject);
    procedure Button4Click(Sender: TObject);
    procedure Button5Click(Sender: TObject);
    procedure Button6Click(Sender: TObject);
    procedure Button7Click(Sender: TObject);
    procedure Button8Click(Sender: TObject);
    procedure Button9Click(Sender: TObject);
    procedure Button10Click(Sender: TObject);
    procedure BitBtn1Click(Sender: TObject);
    procedure FormCreate(Sender: TObject);
  private
    { Private-Deklarationen }
  public
    { Public-Deklarationen }
  end;

var
  Form1: TForm1;
  PIN_EINGABE, PIN_ECHT:word;
  Kontostand, Abheben, Kredit:word;
  Anzahl:byte;


implementation

{$R *.dfm}


procedure TForm1.Button1Click(Sender: TObject);
begin
if Length(Edit1.text)< 4 then Edit1.text:=Edit1.text + '1'
end;

procedure TForm1.Button2Click(Sender: TObject);
begin
if Length(Edit1.Text)< 4 then Edit1.Text:=Edit1.Text + '2'
end;

procedure TForm1.Button3Click(Sender: TObject);
begin
if Length(Edit1.Text)< 4 then Edit1.Text:=Edit1.Text + '3'
end;

procedure TForm1.Button4Click(Sender: TObject);
begin
if Length(Edit1.Text)< 4 then Edit1.Text:=Edit1.Text + '4'
end;

procedure TForm1.Button5Click(Sender: TObject);
begin
if Length(Edit1.Text)< 4 then Edit1.Text:=Edit1.Text + '5'
end;

procedure TForm1.Button6Click(Sender: TObject);
begin
if Length(Edit1.Text)< 4 then Edit1.Text:=Edit1.Text + '6'
end;

procedure TForm1.Button7Click(Sender: TObject);
begin
if Length(Edit1.Text)< 4 then Edit1.Text:=Edit1.Text + '7'
end;

procedure TForm1.Button8Click(Sender: TObject);
begin
if Length(Edit1.Text)< 4 then Edit1.Text:=Edit1.Text + '8'
end;

procedure TForm1.Button9Click(Sender: TObject);
begin
if Length(Edit1.Text)< 4 then Edit1.Text:=Edit1.Text + '9'
end;

procedure TForm1.Button10Click(Sender: TObject);
begin
if Length(Edit1.Text)< 4 then Edit1.Text:=Edit1.Text + '0'
end;

procedure TForm1.BitBtn1Click(Sender: TObject);
begin
PIN_ECHT:=2288;
PIN_EINGABE:=strtoint(edit1.text);
  if PIN_EINGABE = PIN_ECHT then
    begin
    edit1.clear;
    label1.caption:='PIN war richtig';
    end
      else
      begin
      label1.caption:='Falsche PIN!';
      edit1.clear;
      edit1.setfocus;
      Anzahl:=Anzahl+1;
      end;
  if Anzahl > 2 then
      begin
      Button1.enabled:=false;
      Button2.enabled:=false;
      Button3.enabled:=false;
      Button4.enabled:=false;
      Button5.enabled:=false;
      Button6.enabled:=false;
      Button7.enabled:=false;
      Button8.enabled:=false;
      Button9.enabled:=false;
      Button10.enabled:=false;
      bitbtn1.enabled:=false;
      edit1.enabled:=false;
      label1.caption:='Kontozugriff gesperrt!';
      end;

end;


procedure TForm1.FormCreate(Sender: TObject);
begin
if edit1.text='' then bitbtn1.enabled:=false
                 else bitbtn1.enabled:=true;
end;

end.                    

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procedure TForm1.FormCreate(Sender: TObject);
begin
  Button1.Enabled:=False;
end;

procedure TForm1.Edit1Change(Sender: TObject);
begin
  if Length(Edit1.Text)> 0 then Button1.Enabled:=True
  else Button1.Enabled:=False;
end;                    

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procedure TForm1.Button1Click(Sender: TObject);    
begin
  if length(Edit1.Text) < 4 then
    begin
      Edit1.Text := Edit1.Text + (Sender as TButton).Caption;     
      panel2.Caption := panel2.Caption + '*';
    end;
end;
// Edit für die "reinen" Zahlen (nicht sichtbar) und Panel als Anzeige                    

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Button1.visible:=false;
Button2.visible:=false;
Button3.visible:=false;
Button4.visible:=false;
Button5.visible:=false;
Button6.visible:=false;
Button7.visible:=false;
Button8.visible:=false;
Button9.visible:=false;
Button10.visible:=false;                    

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procedure TForm1.Button6Click(Sender: TObject);
var
 i:Integer;
begin
  for i:= 1 to 5 do
  TButton(FindComponent('Button'+IntToStr(i))).Visible := False;
end;                    

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procedure TForm1.Button1Click(Sender: TObject);
begin
if Length(Edit1.text)< 4 then Edit1.text:=Edit1.text + '1'
end;

procedure TForm1.Button2Click(Sender: TObject);
begin
if Length(Edit1.Text)< 4 then Edit1.Text:=Edit1.Text + '2'
end;

procedure TForm1.Button3Click(Sender: TObject);
begin
if Length(Edit1.Text)< 4 then Edit1.Text:=Edit1.Text + '3'
end;

procedure TForm1.Button4Click(Sender: TObject);
begin
if Length(Edit1.Text)< 4 then Edit1.Text:=Edit1.Text + '4'
end;

procedure TForm1.Button5Click(Sender: TObject);
begin
if Length(Edit1.Text)< 4 then Edit1.Text:=Edit1.Text + '5'
end;

procedure TForm1.Button6Click(Sender: TObject);
begin
if Length(Edit1.Text)< 4 then Edit1.Text:=Edit1.Text + '6'
end;

procedure TForm1.Button7Click(Sender: TObject);
begin
if Length(Edit1.Text)< 4 then Edit1.Text:=Edit1.Text + '7'
end;

procedure TForm1.Button8Click(Sender: TObject);
begin
if Length(Edit1.Text)< 4 then Edit1.Text:=Edit1.Text + '8'
end;

procedure TForm1.Button9Click(Sender: TObject);
begin
if Length(Edit1.Text)< 4 then Edit1.Text:=Edit1.Text + '9'
end;

procedure TForm1.Button10Click(Sender: TObject);
begin
if Length(Edit1.Text)< 4 then Edit1.Text:=Edit1.Text + '0'
end;                    

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if Length(Edit1.Text)< 4 then Edit1.Text:=Edit1.Text + (sender as TButton).Caption;