procedure TfrmPetrolDisplay.Timer1Timer(Sender: TObject);
Var
  LitresStr:String;
  n1:char;
  n2:char;
  n3:char;
begin
  Litres:=Litres+1;
  LitresStr:=IntToStr(litres);
 
While Length(litresStr) <=3 do
  LitresStr:='0'+LitresStr;
 
n1:=LitresStr[1];
n2:=LitresStr[2];
n3:=LitresStr[3];
Begin
Case n1 Of
'0':Img1.picture.loadfromfile('0.bmp');
'1':Img1.picture.loadfromfile('1.bmp');
'2':Img1.picture.loadfromfile('2.bmp');
'3':Img1.picture.loadfromfile('3.bmp');
'4':Img1.picture.loadfromfile('4.bmp');
'5':Img1.picture.loadfromfile('5.bmp');
'6':Img1.picture.loadfromfile('6.bmp');
'7':Img1.picture.loadfromfile('7.bmp');
'8':Img1.picture.loadfromfile('8.bmp');
'9':Img1.picture.loadfromfile('9.bmp');
End;
 
Begin
Case n2 Of
'0':Img2.picture.loadfromfile('0.bmp');
'1':Img2.picture.loadfromfile('1.bmp');
'2':Img2.picture.loadfromfile('2.bmp');
'3':Img2.picture.loadfromfile('3.bmp');
'4':Img2.picture.loadfromfile('4.bmp');
'5':Img2.picture.loadfromfile('5.bmp');
'6':Img2.picture.loadfromfile('6.bmp');
'7':Img2.picture.loadfromfile('7.bmp');
'8':Img2.picture.loadfromfile('8.bmp');
'9':Img2.picture.loadfromfile('9.bmp');
End;
 
Begin
Case n3 Of
'0':Img3.picture.loadfromfile('0.bmp');
'1':Img3.picture.loadfromfile('1.bmp');
'2':Img3.picture.loadfromfile('2.bmp');
'3':Img3.picture.loadfromfile('3.bmp');
'4':Img3.picture.loadfromfile('4.bmp');
'5':Img3.picture.loadfromfile('5.bmp');
'6':Img3.picture.loadfromfile('6.bmp');
'7':Img3.picture.loadfromfile('7.bmp');
'8':Img3.picture.loadfromfile('8.bmp');
'9':Img3.picture.loadfromfile('9.bmp');
End;
End;
End;
End;
End;
end.

type
  TfrmPetrolDisplay = class( TForm )
    private
      f_images: array[ 1..3 ] of tImage;
      f_digits: array[ 0..9 ] of tBitmap;
    ...
    end;
 
...
 
procedure TfrmPetrolDisplay.FormCreate( sender: tObject );
  var cntr: integer;
  begin
  // Initialize our "easy access" images array
  f_images[ 1 ] := Img1;
  f_images[ 2 ] := Img2;
  f_images[ 3 ] := Img3;
 
  // Load all bitmaps from file or resource or wherever you keep them
  // (this example loads from file)
  for cntr := 0 to 9 do begin
    f_digits[ cntr ] := tBitmap.create;
    f_digits[ cntr ].loadFromFile( intToStr( cntr ) +'.bmp' )
    end
  end;
 
...
 
procedure TfrmPetrolDisplay.FormDestroy( sender: tObject );
  var cntr: integer;
  begin
  // clean up our digits images
  for cntr := 0 to 9 do f_digits[ cntr ].free
  end;
 
...
 
procedure TfrmPetrolDisplay.Timer1Timer( sender: tObject );
  var
    cntr: integer;
    LitresStr: string;
  begin
  Litres := Litres +1;
 
  // Convert number of liters to a 3-digit number
  LitresStr := intToStr( Litres );
  LitresStr := stringOfChar( '0', 3 -length( LitresStr ) ) +LitresStr;
 
  // Set each of the displayed digit images
  for cntr := 1 to 3 do
    f_images[ cntr ].picture.bitmap.assign( f_digits[ cntr ] )
  end;