Convert binary to decimals

For example, 1101 is a 1*10^0+0*10^1+1*10^2+1*10^3 So, inplementation of this algorithm is so:

function Pow(i, k: Integer): Integer;
var
  j, Count: Integer;
begin
  if k>0 then j:=2
    else j:=1;
  for Count:=1 to k-1 do
    j:=j*2;
  Result:=j;
end;

function BinToDec(Str: string): Integer;
var
  Len, Res, i: 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;