Toggle between dotted lines/solution/blank space

Question

I want to learn how to create a command such that I can easily toggle between having dotted lines or solution or even blank space (no space) under my questions.

I know exam class has the answer argument that allows you to display your solution under the question but that only does half the job as it also displays the dotted lines above.

My MWE:

\documentclass[a4paper,answers,12pt]{exam}

\begin{document}
\begin{questions}
    \question[1] $1+1$?
    \begin{choices} \choice 1\correctchoice 2\choice 3\choice 4\end{choices}
    \question[1]
    What is $1+1$?
    \fillwithdottedlines{2cm}
    \begin{solution}
        $2$
    \end{solution}
    \question Answer the following questions.
    \begin{parts}
        \part[1] What is $1-1$?
        \fillwithdottedlines{2cm}
            \begin{solution}
            $2$
            \end{solution}
    \end{parts}
\end{questions}
\end{document}

Ideally, I want to learn how to create a command that can easily toggle between these three states.

Answer 1

Here is one approach.

We define a new " if " dotsolution, using the ifthen package which exam already loads. Then, we store the old definition of \solution (what happens at \begin{solution), and add stuff to it. The stuff we add checks both \ifdotsolution and \ifprintanswers. If \ifprintanswers is true, we skip straight to the solution. If not, we check \dotsolution; if that is true, we print the dots, else we do nothing.

So, to toggle the 3 cases you can: a) use the answers option, b) don't use answers and set \dotsolutionfalse, or c) don't use answers and set \dotsolutiontrue.

Bonus: We add an argument to \begin{solution} for the height of \fillwithdottedlines. But of course, you can remove it and hardcode a value if you prefer.

\documentclass[a4paper,12pt]{exam}

\newif\ifdotsolution
\dotsolutiontrue
\let\osolution\solution
\def\solution#1{%
  \ifprintanswers\else%
    \ifdotsolution%
      \fillwithdottedlines{#1}%
    \fi%
  \fi%
  \osolution%
}

\begin{document}
\begin{questions}
  \question[1] $1+1$?
    \begin{choices}
      \choice 1
      \correctchoice 2
      \choice 3
      \choice 4
    \end{choices}
  \question[1] What is $1+1$?
    \begin{solution}{2cm}
      $2$
    \end{solution}
  \question Answer the following questions.
    \begin{parts}
      \part[1] What is $1-1$?
        \begin{solution}{2cm}
          $2$
        \end{solution}
    \end{parts}
\end{questions}
\end{document}