program Slysim;
uses
  Crt;
Var
  i : integer;
begin
Window(1, 1, 80, 25);
TextBackGround(3);
TextColor(13);
ClrScr;
For i := 20 to 20000 do begin
       GotoXY(38,13);
       Write(i, ' Hz');
       Sound(i);
       Delay(10);
       if keypressed then break;  {break vyskoci z cyklu}
End;
NoSound;
end.