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Does anyone know how to invert a boolean in LaTeX? It looks like once you are inside a logical test, resetting the logical value has no effect. Using the etoolbox package, I tried

\foreach \n in {1,2,3,4,5,5,6,7,8,9,e}{ \iftoggle{pauper}{ True \togglefalse{pauper} }{ False \toggletrue{pauper} } }

It should produce True False True False True False True False True False, but produces only a string of ten True. How can I make it come out True False True False ....

If this problem is solved, I can solve a far larger problem. It might be that the larger problem has a more elegant solution I have not though of, so I state it as well:

The context is a textbook, where I write the assignment and the answer together, and then call the assignment file twice. The first time, the boolean value assignment is true, the second time it is false.

\begin{enumerate} \item \ifthenelse{assignment}{$2+2$}{$4$} ... \end{enumerate}

Now, I would like for the answers section to have answers to only the odd numbered problems, except for a teacher's version which would have all. So the \item should ideally be something like this

 % if assignment=false, then ... % if item counter is odd: \item \ifthenelse{assignment}{$2+2$}{$4$} % but if item counter is odd: \stepcounter{enumi} % if assignment=true, then, regardless of counter: \item \ifthenelse{assignment}{$2+2$}{$4$}

I have tried

 \ifthenelse{\boolean{assignment}}{$2+2$}{ \ifthenelse{\boolean{oddItem}}{ \item $4$ \setboolean{oddItem}{false} }{ \stepcounter{enumi} \setboolean{oddItem}{true} } }

But the boolean stays the same value. I have tried several combinations, and also setting it outside the inner ifthenelse like this,

\setboolean{oddItem}{\not\boolean{oddItem}}

but to no avail. Same with toggle instead of boolean.

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1 Answer 1

Reset to default
1

First, the body of \foreach is in a group so the effect of local commands is restricted to a single iteration. What it means for your first example is that \toggletrue/\togglefalse only have an effect within the same iteration. To fix this, as suggested in the etoolbox manual, you can prefix them with \global which extends their effect beyond groups:

\foreach \n in {1,2,3,4,5,5,6,7,8,9,e}{ \iftoggle{pauper}{ True \global\togglefalse{pauper} }{ False \global\toggletrue{pauper} } }

shoud give the desired result.

Without further context, a simpler solution can be provided by using LaTeX \newif and \ifodd without the need for etoolbox and ifthenelse.

First you can create a new conditional with \newif\ifassignment and set it to true or false using \assignmenttrue \assignmentfalse. Then, if you have a counter (either \theenumi or \n in your \foreach) you can check if it is odd by using \ifodd.

\begin{itemize} \foreach\n in {1,...,10}{ \item Problem \n \ifassignment% \ifodd\n% \relax% \else% -- Solution \n% \fi \else% -- Solution \n% \fi% } \end{itemize}

The ugly part is that the solution has to be repeated twice. THere are multiple ways to solve this but the way I am presenting is by introducing a macro \printproblem that encapsulates this logics:

\newcommand{\printproblem}[2]{ \item #1% \ifassignment% \ifodd\n% -- #2% \else% \relax% \fi \else% -- #2% \fi% }

An then you can do

\begin{itemize} \foreach\n in {1,...,10}{ \printproblem{Problem \n}{Solution \n} } \end{itemize}

If you are not using an actual \foreach loop, you can use \theenumi instead of \n:

\newcommand{\solution}[1]{ \ifassignment% \ifodd\theenumi% -- #1% \else% \relax% \fi \else% -- #1% \fi% }

and in the body:

\begin{enumerate} \item Problem 1 \solution{Solution 1} \item Problem 2 \solution{Solution 2} \item Problem 3 \solution{Solution 3} \item Problem 4 \solution{Solution 4} \item Problem 5 \solution{Solution 5} \end{enumerate}
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  • I am not using the foreach loop, so the latter is more like what I am doing. To be precise, I have defined two boolean variables, that turn on and off the visibility of two environments, oText and oSolution. An assignment looks like this: \item Description \oText{$2+2$}\oSolution{$4$} The file is called twice: first with Text on, Solution off. Then later with Solution on, Text off. I will try to tweak your solution command, so that it's on when Text is, and has \item inside. Then item calls will be like this: \solution{ \item Description \oText{$2+2$}\oSolution{$4$} } Look OK? Commented May 1, 2016 at 11:04
  • If you make progress but find other problems you can always post a new question. I believe the first part of my answer addresses your question quite directly. If this answered your question please consider marking it as an accepted answer. Commented May 1, 2016 at 16:10

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