Showing Solutions of the Questions “separately”

Question

There is a class for LaTeX called exam. Using this class, one can write questions and answers for exams. The answers are displayed under (after) each question. My goal is to have all answers in the separate part of the document (after all questions). For that purpose I tried to create new environment like this:

\newenvironment{answer}{\def\answertext\begingroup}{\endgroup}

I was hoping to gather answer text into \answertext and dump it after all questions. I'm sure, a solid TeX Package/Class writer can do it within no time... Please, give me some hint.

Answer 1

We accumulate all the answers in a \vbox, and then dump the contents out of the \vbox and onto the page when it's appropriate. (Thus, when the answers actually hit the page, they're not inside of the \vbox, and so there's no interference with pagebreaks.)

Here's a complete LaTeX file that demonstrates the idea:

\documentclass{exam}

\newbox\allanswers
\setbox\allanswers=\vbox{}

\newenvironment{answer}
{%
  \global\setbox\allanswers=\vbox\bgroup
  \unvbox\allanswers
}%
{%
  \bigbreak
  \egroup
}

\newcommand{\showallanswers}{\par\unvbox\allanswers}


%--------------------------------------------------------------------
\begin{document}

\begin{questions}
  \question Why is there air?

  \begin{answer}
    Answer to Question \thequestion:

    There's air so that we can blow up volleyballs and basketballs.
  \end{answer}

  \question Who's buried in Grant's tomb?
  \begin{answer}
    Answer to Question \thequestion:

    What's his name.
  \end{answer}

  \question What was the color of George Washington's white horse?
  \begin{answer}
    Answer to Question \thequestion:

    Blue.  (No; Yellow!!)
  \end{answer}
\end{questions}

\bigskip
\begin{center}
  Here are the answers:
\end{center}
\showallanswers







\end{document}

Answer 2

The \def macro doesn't accept \begingroup...\endgroup instead of { }. No macro does. Some macros (like \hbox) accept \bgroup and \egroup which are implicit braces, i.e. created using \let\bgroup={ and \let\egroup=} (the = is optional).

To store the content of an environment use the environ package which was created for this purpose. The content is presented as \BODY which can be copied to \answertext. Keep in mind that the code is executed inside the environment, i.e. in a group, therefore \global\let\answertext\BODY or \xdef\answertext{\BODY} must be used. However, this only allows one answer text to be stored. If you want to accumulate answers use either \g@addto@macro<macro>{<code>}, e.g. \expandafter\g@addto@macro\expandafter\answertext\expandafter{\BODY} or the \xappto macro of the etoolbox package.

Some example (without the exam class):

\documentclass{article}

\usepackage{environ}

\newcommand{\answertext}{}
\NewEnviron{answer}{\global\let\answertext\BODY}
% or
\makeatletter
\NewEnviron{answer}{\expandafter\g@addto@macro\expandafter\answertext\expandafter{\BODY}}%
\makeatother
% or
\usepackage{etoolbox}
\NewEnviron{answer}{\xappto\answertext{\expandonce{\BODY}}}%


\begin{document}

The question
\begin{answer}
  The answer text
\end{answer}

\newpage
% Some time later
\answertext


\end{document}

Answer 3

My file ans.sty at http://www.cwru.edu/artsci/math/wells/pub/mytex.html is old but I use it regularly to this day. It can no doubt be modified to do what you want.