[ Binary -> Decimal ]
function Pow( i, k : Integer): Integer;
var
  j,
  liCount : Integer;
begin
  if k > 0 then
     j := 2
  else
     j := 1;

  for liCount := 1 to k - 1 do
     j := j * 2;

  Result := j;
end;

function BinToDec( Str : String ) : Integer;
var
  i,
  Len,
  Res : Integer;
  Error: Boolean;
begin
  Error := False;
  Len := Length( Str );
  Res := 0;

  for i := 1 to Len do
     if ( Str[ i ] = '0' ) OR
        ( Str[ i ] = '1' ) then
        Res := Res + Pow( 2, Len - i ) * StrToInt( Str[ i ] )
     else
     begin
        MessageDlg( 'It is not a binary number', mtInformation, [ mbOK ], 0 );
        Error := True;
        Break;
     end;

  if Error = True then
     Result := 0
  else
     Result := Res;
end;

procedure TForm1.Button1Click(Sender: TObject);
begin
  if Edit1.Text<>'' then
    Label2.Caption:=IntToStr( BinToDec( Edit1.Text ) );
end;

[ Decimal -> Binary ]
function TForm1.DecToBinStr( N : Integer ) : string;
var
  S: string;
  i: Integer;
  Negative: Boolean;
begin
  if N<0 then Negative:=True;
  N:=Abs(N);
  for i:=1 to SizeOf(N)*8 do
  begin
    if N<0 then S:=S+'1'
    else S:=S+'0';
    N:=N shl 1;
  end;
  Delete(S,1,Pos('1',S)-1);
  if Negative then S:='-'+S;
  Result:=S;
end;