Setting new environments with LaTeX

Question

I was attempting to simplify my LaTeX document to write a Maths assessment with LaTeX, but when I created new environments I got an error that I cannot solve. Can you please explain me what is wrong with my definition? The source is the following:

\documentclass{article}
\usepackage{tabu}
\usepackage{longtable}

% ASSESSMENT TEXT
\newenvironment{assessment}
    {\tabulinesep=1.5mm
     \begin{longtabu} to \linewidth{|X[13 l]|X[c]|}
     \hline
      & \scriptsize DO NOT WRITE IN THIS MARGIN \cr}
    {\end{longtabu}}

% Pattern \begin{AssExer}{mark}{space}
\newcounter{exercise}
\newenvironment{AssExerc}[2]
    {\hline
     \begin{minipage}[t]{\linewidth}
     \refstepcounter{exercise}\textbf{\theexercise.}~}
    {\end{minipage}\vspace{#2} & \textbf{#1}\cr
     \hline}

\begin{document}
\begin{assessment}
\begin{AssExerc}{1}{2cm}
Solve the following equation $2x-1 = 0$.
\end{AssExerc}
\end{assessment}
\end{document}

The assessment environment works, but the AssExerc doesn't. Thank you for your help.

Answer 1

There's a few problems with your code. First, you cannot use an argument to an environment in the \end{environment} code. We can get around this by putting the arguments into temporary global variables \gdef\temppoints{#1}\gdef\tempvskip{#2}.

The second more bothersome issue is that the environment starts a group and inside that group you cannot add elements to the table like & or \cr or \hline. To get around this, we can use \AfterEndEnvironment which adds code after the environment group is ended and is defined in the etoolbox package. We need to move & \textbf{#1}\cr\hline into \AfterEndEnvironment. I don't have a similar workaround for the \hline in the \begin{AssExer} part, but luckily that \hline is unneeded.

\documentclass{article}

\usepackage{tabu}
\usepackage{longtable}
\usepackage{etoolbox}

% ASSESSMENT TEXT
\newenvironment{assessment}
    {\tabulinesep=1.5mm
     \begin{longtabu} to \linewidth{|X[13 l]|X[c]|}
     \hline
      & \scriptsize DO NOT WRITE IN THIS MARGIN \cr\hline}
    {\end{longtabu}}

% Pattern \begin{AssExer}{mark}{space}
\newcounter{exercise}
\newenvironment{AssExer}[2]{
     \begin{minipage}[t]{\linewidth}
     \refstepcounter{exercise}\textbf{\theexercise.}~
     \gdef\temppoints{#1}\gdef\tempvspace{#2}
}{
     \end{minipage}\vspace{\tempvspace} 
}
\AfterEndEnvironment{AssExer}{& \textbf{\temppoints}\cr\hline}

\begin{document}

\begin{assessment}
\begin{AssExer}{1}{2cm}
Solve the following equation $2x-1 = 0$.
\end{AssExer}
\end{assessment}

\end{document}