Solutions Page Not Compiling

Question

I am creating exercise worksheets with solutions for students to practice determining equations from linear graphs.

But my solutions page is not compiling... again. [Previous post.]

I replaced all the \( and \) with $ and have double checked the code... so I think I'm not making the same mistake again.

Does anybody know what's going wrong?

\documentclass{article}

\usepackage{amssymb}
 \newcommand{\reals}{\mathbb{R}}
\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.

   \ifthenelse{\equal{\xvar}{0}}{$y_{int} \in \reals $}{There is no $y_{int}$.}

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


\newcommand{\ManySolutions}{}

\newcommand{\ManyExercises}[1]
{%
  \foreach \x in {1,...,#1}
  {%
   \VertLine \Exercise \par \vspace{5cm}
   \xdef\ManySolutions{\ManySolutions \Solution \par} 
  }
}



\begin{document}

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

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

\end{document}

Answer 1

Edit After accepted New code that doesn't use Reals symbol and doesn't produce any error:

\documentclass{article}

\usepackage{amssymb}
\let\origmathbb\mathbb
\usepackage{ifthen}
\usepackage{pgf}
 \pgfmathsetseed{\number\pdfrandomseed}
\usepackage{pgffor}
\usepackage{tikz}


\xdef\Reals{\noexpand\origmathbb{R}}

\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} \in Reals $}\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{5cm}
   \edef\oldManySolutions{\ManySolutions}
   \xdef\ManySolutions{\oldManySolutions \Solution  \par} 
  }
}





\begin{document}

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

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

\end{document}

Here is a solution which doesn't use \ifthenelse but \ifnum instead.

I found by debuging that this command was causing the problem and replaced it with \ifnum

\documentclass{article}

\usepackage{amssymb}
 \newcommand{\reals}{\mathbb{R}}
\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} \in \reals $}
   \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{5cm}
   \xdef\ManySolutions{\ManySolutions \Solution \par} 
  }
}



\begin{document}

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

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

\end{document}