procedure TForm1.Button1Click(Sender: TObject);
var used : array [0..9] of boolean;
     i,t : shortint;
     int : integer;
begin
    Randomize();
    for i:=0 to 9 do
       used[i]:=false;

    t:=1+Random(10);
    int:=0;
    for i:=0 to 3 do begin
       while (used[t]) do
          t:=Random(10);
       used[t]:=true;
       int:=int*10+t;
    end;
    label1.Caption:=inttostr(int);

end;