Delphi function to check a string if it's number

function IsNumber(Text: String): Boolean;

var i: Integer;

    c: char;

begin

  Result := True;

  if Length(Text) <= 0 then

    Result := False;

  for i := 1 to Length(Text) do

  begin

    c := Text[i];

    if not ((c >= '0') and (c <= '9')) then

    if not ((c = DecimalSeparator) and (i > 1)) then

    if not ((c = '-') and (i = 1)) then

    if not ((c = '+') and (i = 1)) then

    begin

      Result := False;

      //Break;

    end;

  end;

end;