You want the comment package. This provides the \includecomment and \excludecomment macros:
\documentclass{article}
\usepackage{comment}
\excludecomment{confidential}
\begin{document}
Some text
\begin{confidential}
Some secret text
\end{confidential}
\end{document}
There are a couple of approaches you can take. Here is a solution which makes use of TeX's \ifcase which can be very nice for this sort of thing:
\documentclass{article}
\usepackage[margin=1in]{geometry}
\newcounter{examquestion}
\newcommand{\question}{\stepcounter{examquestion}\noindent\textbf{Q\theexamquestion.)}\hspace*{1em}}
\newcommand{\answers}[1][\theexamquestion]{%
\ifcase#1\relax{This would be the answer to question 0: I presume there is no question 0}
\or{Answer to question 1}%
\or{Answer to question 2}%
\or{Answer to question 3}%
\or{Answer to question 4}%
\fi}%'
%% for purposes of this example only
\usepackage{lipsum}
\pagestyle{empty}
\begin{document}
\question \lipsum[1]
\par\hspace*{\fill}\textbf{Answer: \answers}
\vspace{0.25in}
\question \lipsum[2]
\par\hspace*{\fill}\textbf{Answer: \answers}
\vspace{0.25in}
\question \lipsum[3]
\par\hspace*{\fill}\textbf{Answer: \answers}
\vspace{0.25in}
Summary:
\begin{itemize}
\item \answers[1]
\item \answers[2]
\item \answers[3]
\end{itemize}
\end{document}
This works nicely if you have a counter for each problem. I've written the \answers command so that it defaults to using the current value of question counter examquestion. But you can override this. As you may notice, I've answered each question when the answer is posed. Maybe this is not what you wanted to do. I've allowed you to overwrite this default. I've illustrated this in the itemized summary.
LaTeX3 answer with a better user interface:
\documentclass{article}
\usepackage[margin=1in]{geometry}
\usepackage{xparse}
\ExplSyntaxOn
%% expl3::warnings and error messages
\msg_new:nnnn {examanswer}{answer_already_defined}{%
You're\ attempting\ to\ define\ an\ answer\ that\
already\ exists.\\
\\
\ \ \ \ Key\ "#1"\ already\ exists.
}{}
\msg_new:nnnn {examanswer}{answer_not_defined}{%
You're\ attempting\ to\ call\ an\ answer\ that\
has\ not\ been\ defined.\\
\\
\ \ \ \ Key\ "#1"\ does\ not\ exist.}{}
%% expl3 code to save and retrieve answers
\prop_new:N \g__answers_to_exam_problems_plist
\cs_new_protected:Npn \__setting_answers_cs:nn #1#2 {
\prop_if_in:NnTF \g__answers_to_exam_problems_plist {#1}
{
\msg_error:nnx{examanswer}{answer_already_defined}{#1}
}
{
\prop_gput:Nnn \g__answers_to_exam_problems_plist {#1} {#2}
}
}
\cs_new_protected:Npn \__getting_answers_cs:n #1 {
\prop_if_in:NnTF \g__answers_to_exam_problems_plist {#1}
{
\prop_get:Nn \g__answers_to_exam_problems_plist {#1}
}
{
\msg_error:nnx {examanswer}{answer_not_defined}{#1}
}
}
%% user interface to save and retrieve answers
\NewDocumentCommand{\saveanswer}{ m m }{
\__setting_answers_cs:nn {#1}{#2}
}
\NewDocumentCommand{\getanswer}{ m }{
\__getting_answers_cs:n {#1}
}
\ExplSyntaxOff
%% a bit of the old version: here purely for the sake of illustration
\newcounter{examquestion}
\newcommand{\question}{\stepcounter{examquestion}\noindent\textbf{Q\theexamquestion.)}\hspace*{1em}}
%% for purposes of this example only
\usepackage{lipsum}
\pagestyle{empty}
\begin{document}
\question \lipsum[1]
\saveanswer{q1ans}{This is the answer to question 1}
\vspace{0.25in}
\question \lipsum[2]
\saveanswer{q2ans}{Answer to question 2}
\vspace{0.25in}
\question \lipsum[3]
\saveanswer{Q:supplementary angles}{$m\angle{ABC}=30$}
\vspace{0.25in}
Summary:
\begin{itemize}
\item \getanswer{q1ans}
\item \getanswer{q2ans}
\item \getanswer{Q:supplementary angles}
\end{itemize}
\end{document}
This approach, I think, is better. It allows you to name the answers to a particular problem independent of the actual numbering of the problems: in this example I nevertheless gave the most answers names which corresponded to the order in which the questions were asked. But there's no reason this code won't let you write,
\setanswer{Q:supplementary angles}{$m\angle{ABC}=30$}
and then later call it with
\getanswer{Q:supplementary angles}
I'd prefer this naming convention since it is more descriptive: and, if later you rearrange the problems, figuring out the meaning of the cryptic \T1 or \getanswer{q1ans} won't be such a hassle.
I've also added some bells and whistles to make sure you don't overwrite previously defined answers and to warn you when calling an undefined answer.
Best Answer
do you mean something like this?
if you have it inside a style file then do something like
to prevent overwriting by a user. Alternatively use
\setmodulecode{}for the first definition.