answers sometimes in test, sometimes in answer file

Question

So this is going to sound strange, but I'm wondering if there is a clean way to do this.

By the time I have a project done, I will have written two .tex files: one with questions, and another one with solutions. For purposes of peer review, I'd like to know if there's a way for me to use \include so that if each question and solution to each respective question spans only one page, the question and solution will be paired together so that the question is first and the solution is second.

Is there a way (or a better way) to do this beside manually copying/pasting code?

MWE:

Questions:

\documentclass[12pt]{article}
\usepackage[margin=2cm]{geometry}
\usepackage{enumitem}

\begin{document}
\begin{center}
\textbf{Mock Exam}
\end{center}
\begin{enumerate} 
\item Here's a question.
\begin{enumerate}[label=(\Alph*)]
\item Option A
\item Option B
\item Option C
\item Option D
\item Option E
\end{enumerate}
\newpage  
\item Here's another question.
\begin{enumerate}[label=(\Alph*)]
\item Option A
\item Option B
\item Option C
\item Option D
\item Option E
\end{enumerate}
\end{enumerate}
\end{document}

Solutions:

\documentclass[12pt]{article}
\usepackage[margin=2cm]{geometry}
\begin{document}
\begin{center}
\textbf{SOLUTION}
\end{center}
\begin{enumerate} 
\item (A)

\vspace{0.2cm}
-Some stuff telling you why the answer is (A)-
\newpage 
\item (C)

\vspace{0.2cm}
-Some stuff telling you why the answer is (C)-
\end{enumerate}
\end{document}

This is the general way I have been creating MC exams and solutions in the past for the company, and it's still very early in the project, so I can change the code so that it works if necessary. It's just that I found it very time-consuming to copy-and-paste the solutions into a new file for peer review.

Answer 1

Try this.

\documentclass{article}
\usepackage{enumitem}
\usepackage{amsmath}
\usepackage{filecontents}
\begin{document}
\begin{filecontents}{question-01}
What is an aardvark?\par
\end{filecontents}
\begin{filecontents}{answer-01}
\pagebreak
The aardvark Orycteropus afer is a medium-sized, burrowing, nocturnal mammal 
\end{filecontents}

% questions and answers here
\input{question-01}
\input{answer-01}
\end{document}

I suggest first to define your requirements clearly, experiment with a main file first and then extend with macros and a naming scheme for the files. I would keep all the answers and questions of one exam in one main file as above. However I would recommend the individual questions and answers are kept in separate files. This way you can mix and match as you go. Keep everything in one directory and name the directory like maths-exam-101-summer-14.

Note you can also relate the files to \jobname as follows:

\begin{filecontents}{\jobname-01-answer}
\pagebreak
The aardvark Orycteropus afer is a medium-sized, burrowing, nocturnal mammal 
\end{filecontents}

\input{question-01}
\input{\jobname-01-answer}

Answer 2

This is a substantial reworking of my original solution - there were fun problems to solve, so I'm posting it even though there's an accepted answer.

The MWE below produces these pdfs as output:

---

---

---

Here are the source files.

First, the test, which you must compile twice to get the references right.

\documentclass{article}

\input{testpreamble}

%\toggletrue{showanswers} % this is the default
\togglefalse{showanswers}

\begin{document}

\testname{Mock Exam}

\begin{enumerate}
\item Compute $2 + 2$.

\begin{choices}
\item 1
\item 2
\item 3
\item 4 \correct{Count on your fingers.}
\item 5
\end{choices}

\item Compute $e^{i\pi}$.

\begin{choices}
\item $e$
\item -1
\correct{
There are several ways to go about proving that

\begin{equation*}
e^{i\pi} = -1
\end{equation*}

but for this exam just \emph{knowing} the answer gets full credit.
}

\item $\pi$
\item whatever
\end{choices}

\item What is the name of this test?
\begin{choices}
\item There is no way to tell
\end{choices}

\end{enumerate}
\end{document}

This document answerkeymaster.tex, produces the answer key:

\documentclass{article}

\begin{document}
\input{answerkey}
\end{document}

The mechanism is all hidden in the testpreamble.tex, which is the same for all tests:

% testpreamble
%
\usepackage{enumitem}
\usepackage{amsmath}
\usepackage{etoolbox}

% decide whether answers appear in the test
\newtoggle{showanswers}
\toggletrue{showanswers}

% does the current question have an answer?
\newtoggle{hasanswer}
\togglefalse{hasanswer}

% file containing answer key is written
\newcommand{\answerkeyfilename}{answerkey}
\newwrite\answerkey
\immediate\openout\answerkey=\answerkeyfilename

\newcommand{\testname}[1]{%
\begin{center}
\textbf{#1}
\end{center}
\immediate\write\answerkey{%
\noexpand\begin{center}
\noexpand\textbf{#1}
\noexpand\par
Answer Key
\noexpand\end{center}
}}

% explanatory words that accompany each answer
\newcommand{\theexplanation}{}

\newcommand{\answer}{%
 \iftoggle{hasanswer}{%
   \immediate\write\answerkey{\noexpand\par\theenumi -- \ref{answer:\theenumi}}
   \iftoggle{showanswers}{%
      \par\emph{Answer}: 
      \ref{answer:\theenumi}
      \theexplanation{}}
   {} % don't show answers
  }
  {\immediate\write\answerkey{\noexpand\par\theenumi -- no answer}
   \iftoggle{showanswers}{%
      \par\emph{Answer}: none }
    {} % don't show nonanswer
  }
}

\newcommand{\correct}[1]{%
 \toggletrue{hasanswer}
 \label{answer:\theenumi}
 \global\renewcommand{\theexplanation}{#1}
}

\newenvironment{choices}
{\begin{enumerate}[label=(\Alph*)]}
{\answer{}\end{enumerate}}

You can probably improve your workflow by implementing some of @YiannisLazarides naming conventions for your tests.