Solutions Will Not Compile

Question

I'm trying to make simple integer exercise pages and solution pages.

Why does this code not compile?

I'm pretty sure the problem is in the \xdef line, but I don't know what the problem is.

Any help would be greatly appreciated. Thanks!

\documentclass{article}

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

\newcommand{\EquationSolution}{}
\newcommand{\EquationExercise}{}

\newcommand{\InitVariables}
{%
 \pgfmathrandominteger{\A}{-10}{10} % the first number
 \pgfmathrandominteger{\C}{-10}{10} % the answer
 \ifthenelse{\equal{\A}{\C}}{\InitVariables}{} 
 \pgfmathsetmacro{\B}{int(\C-\A)} % The second number

 \renewcommand{\EquationExercise}
  {%
   \ifthenelse{\B<0}
   {\Large $\A\B=\_\_\_$}
   {\Large $\A+\B=\_\_\_$}
  }

 \renewcommand{\EquationSolution}
  {%
   \ifthenelse{\B<0}
   {\Large $\A\B=\C$}
   {\Large $\A+\B=\C$}
  }
}


\newcommand{\ManySolutions}{}

\newcommand{\ManyExercises}[1]
{%
 \foreach \x in {1,...,#1}
  {%
   \InitVariables \EquationExercise
   \xdef\ManySolutions{\ManySolutions \EquationSolution} % Compiles if this line is commented out [along with the other line below]
  }
}


\setlength\parindent{0pt}
\pagestyle{empty}


\begin{document}
\section*{Exercises}
\ManyExercises{5}
\section*{Solutions}
\ManySolutions % also must be commented out to compile
\end{document}

Answer 1

The first thing that breaks within \xdef is \ifthenelse, then also \Large and \_.

For \Large it's easy: it doesn't belong there, but to an environment around the commands for calling \ManyExercises and \ManySolutions.

For the other pieces:

\documentclass{article}

\usepackage{pgfmath}
\usepackage{pgffor}

\pgfmathsetseed{\number\pdfrandomseed}

\newcommand{\EquationSolution}{}
\newcommand{\EquationExercise}{}
\newcommand{\ManySolutions}{}
\protected\def\dummy{\makebox[2em]{\hrulefill}}

\newcommand{\InitVariables}
{%
 \pgfmathrandominteger{\A}{-10}{10} % the first number
 \pgfmathrandominteger{\C}{-10}{10} % the answer
 \ifnum\A=\C\relax\InitVariables\fi
 \pgfmathsetmacro{\B}{int(\C-\A)} % The second number

 \edef\EquationExercise
  {%
   $\A\ifnum\B<0 \else +\fi\B=\dummy$\par
  }

 \edef\EquationSolution
  {%
   $\A\ifnum\B<0 \else +\fi\B=\C$
  }
}



\newcommand{\ManyExercises}[1]
{%
 \foreach \x in {1,...,#1}
  {%
   \InitVariables \EquationExercise
   \toks0=\expandafter{\ManySolutions\par}
   \xdef\ManySolutions{\the\toks0 \unexpanded\expandafter{\EquationSolution}} % Compiles if this line is commented out [along with the other line below]
  }
}


\setlength\parindent{0pt}
\pagestyle{empty}


\begin{document}
\section*{Exercises}
{\Large\ManyExercises{5}\par}
\section*{Solutions}
{\Large\ManySolutions\par}
\end{document}