Answer Page Not Working

Question

I'm developing worksheets for students to practice determining equations of lines.

Everything is working except for the last command \ManySolutions. In fact, the code compiles without it.

Does anyone know what's wrong? Is there some incompatibility with $$ vs \(\) or is \foreach incompatible with some other command I put in there?

\documentclass{article}

\usepackage{ifthen}
\usepackage{pgf}
 \pgfmathsetseed{\number\pdfrandomseed}
\usepackage{pgffor}
\usepackage{tikz}

\newcommand{\MyScale}{0.4}

\newcommand{\VertLine}
{%
%
 \pgfmathrandominteger{\xvar}{-9}{9}
%
 State the slope, $y_{int}$, and equation in slope-intercept form.

 \newcommand{\Exercise}
  {%
   \begin{tikzpicture}[scale=\MyScale]
   \draw[help lines, gray, thin] (-10,-10) grid  (10,10); 
   \draw[very thick,<->] (-10.3,0)--(10.3,0);
   \draw[very thick,<->] (0,-10.3)--(0,10.3);
   \draw[thick, blue] (\xvar,-10)--(\xvar,10);
   \end{tikzpicture}%
  }
%
 \newcommand{\Solution}
  {%
   Slope is undefined.

   \ifnum\xvar=0
   {$y_{int}$ is all real numbers.}
   \else
   {There is no $y_{int}$.}
   \fi

   Equation: $x=\xvar$%
   \vspace{1cm}
 }
}


\newcommand{\ManySolutions}{}

\newcommand{\ManyExercises}[1]
{%
  \foreach \x in {1,...,#1}
  {%
   \VertLine \Exercise \par \vspace{0.5cm}
   \xdef\ManySolutions{\ManySolutions \Solution \par} 
  }
}


\begin{document}

\ManyExercises{15}

\ManySolutions


%It does compile if I replace the two lines above with:
 % \VertLine
 % \Exercise
 % \Solution

% So I know the graph and solutions can be generated.

\end{document}

Answer 1

Here is my working results for now:

\documentclass{article}

\usepackage{amssymb}
\usepackage{pgf}
 \pgfmathsetseed{\number\pdfrandomseed}
\usepackage{pgffor}
\usepackage{tikz}



\newcommand{\MyScale}{0.4}

\newcommand{\Exercise}{}
\newcommand{\Solution}{}
\newcommand{\VertLine}
{%
%
 \pgfmathrandominteger{\xvar}{-9}{9}
%
 State the slope, $y_{int}$, and equation in slope-intercept form.

 \renewcommand{\Exercise}
  {%
   \begin{tikzpicture}[scale=\MyScale]
   \draw[help lines, gray, thin] (-10,-10) grid  (10,10); 
   \draw[very thick,<->] (-10.3,0)--(10.3,0);
   \draw[very thick,<->] (0,-10.3)--(0,10.3);
   \draw[thick, blue] (\xvar,-10)--(\xvar,10);
   \end{tikzpicture}%
  }
%
 \renewcommand{\Solution}
  {%
   Slope is undefined.
   \ifnum\xvar=0 $y_{int}$ is all real numbers \else There is no $y_{int}$.\fi

   Equation: $x=\xvar$
   \vskip 1cm

 }
}


\newcommand{\ManySolutions}{}



\newcommand{\ManyExercises}[1]
{%
  \foreach \x in {1,...,#1}
  {%
   \VertLine \Exercise \par \vspace{0.5cm}
   \xdef\ManySolutions{\ManySolutions \Solution\par} 
  }
}

%\renewcommand{\ManyExercises}[1]
%{%
%  \newcount\X
%  \X=1
%  \loop
%  \advance \X by 1
%   \VertLine \Exercise \par \vspace{5cm}
%   \edef\oldManySolutions{\ManySolutions}
%   \xdef\ManySolutions{\oldManySolutions \Solution\par }
%  \ifnum\X<#1
%  \relax
%  \repeat
%}





\begin{document}

%This does not compile...%%%Compiles now
\ManyExercises{10}


\ManySolutions
%It does compile if I replace the line above with:
%% \VertLine
%% \Exercise
%% \Solution

\end{document}

The commented way of \ManyExercises gives the same results as the above. This way I found out that the problem which remains is the \vspace{1cm} that I have commented out. Of course there is no spaces in the results.

Edit Replacing \vspace{1cm} with \vskip gives the wanted result