newcommand putting strange space before text

Question

I'm trying to do the usual "make a worksheet with blank spaces", and I need blanks longer than the text which will eventually fill them (so that students can write in answers by hand). Unfortunately, my command "blank" prints a strange amount of space before evaluating in the text. If I just insert the same command in the body, it evaluates normally.

    \documentclass[]{article}
    \newlength\mylen
    \newlength\fieldlen
    \newcommand\blank[1]{%
       \settowidth\mylen{#1}
       \settowidth\fieldlen{0}
       \addtolength\fieldlen{\mylen}
       \addtolength\fieldlen{\mylen}
       \underline{\makebox[\fieldlen]{}}    %comment this line and uncomment next line to hide answers
       %\underline{\makebox[\fieldlen]{#1}} %comment this line and uncomment previous line to show answers
    }
    \begin{document}

Using the macro, I get the following:

We find that $G<$\blank{$G_1$}.

There's an extra space before the underline. 

I want it to look like:

We find that $G<$\underline{\makebox[\fieldlen]{}}.
\end{document}

Answer 1

The usage of the macros \settowidth and \addtolength is missing a % at the end, so 4 missing % will lead to one additional space character each.

As well there is a missing % after \underline, so the . is shifted to the right.

  \documentclass[]{article}
  \newlength\mylen
  \newlength\fieldlen
  \newcommand\blank[1]{%
    \settowidth{\mylen}{#1}%
    \settowidth{\fieldlen}{0}%
    \addtolength{\fieldlen}{\mylen}%
    \addtolength{\fieldlen}{\mylen}%
    \underline{\makebox[\fieldlen]{}}%    %comment this line and uncomment next line to hide answers
    % \underline{\makebox[\fieldlen]{#1}} %comment this line and uncomment previous line to show answers
  }
  \begin{document}

Using the macro, I get the following:

We find that $G<$\blank{$G_1$}.

There's an extra space before the underline. 

I want it to look like:

We find that $G<$\underline{\makebox[\fieldlen]{}}.
\end{document}