etoolbox: trouble with boolean expressions

Question

I'm new at making macros and am in the process of building a package to produce course outlines. I want the user to input room/day/time information as below (where everything has been simplified to just using the room)

\newcounter{RoomCount}
\NewDocumentCommand\Room{R(){TBA}}{%
    \stepcounter{RoomCount}%
    \expandafter\newcommand\csname Room\theRoomCount\endcsname{#1}%
}

At this point I would like to feed this information into a tabular environment to format the room/day/time information. To do so, I would like a macro that spits out 1 row for each room/day/time combination that has been input. This macro would then be executed in a tabular environment to build the table.

\NewDocumentCommand\buildrows{}{%
\newbool{myBool}%
\booltrue{myBool}%
\newcounter{rownum}%
\whileboolexpr{myBool}{%
    \stepcounter{rownum}%
    \ifcsdef{Room\therownum}%
    {\csname Room\therownum\endcsname\\}%
    {\boolfalse{myBool}}%
}%
}

The intention of the loop is: check whether the user has input a second room, if so, then write a row for tabular, if not, then set myBool to false so that the loop exits. The following, however, produces many "package etoolbox error: invalid boolean expression" errors

\begin{document}
\Room(C244)

\begin{tabular}{l}
  \buildrows{}
\end{tabular}

\end{document}

At this point I don't have enough "tools in my toolbox" to figure out what I'm doing wrong so any help/suggestions would be greatly appreciated. Thanks! ps. The full example would be:

\documentclass{report}
\usepackage{xparse}
\usepackage{etoolbox}

\newcounter{RoomCount}
\NewDocumentCommand\Room{+R(){TBA}}{%
\stepcounter{RoomCount}%
\expandafter\newcommand\csname Room\theRoomCount\endcsname{#1}%
}

\NewDocumentCommand\buildrows{}{%
\newbool{myBool}%
\booltrue{myBool}%
\newcounter{rownum}%
\whileboolexpr{myBool}{%
    \stepcounter{rownum}%
    \ifcsdef{Room\therownum}%
    {\csname Room\therownum\endcsname}%
    {\boolfalse{myBool}}%
}%
}

\begin{document}
\Room(C244)

\begin{tabular}{l}
\buildrows{}
\end{tabular}

\end{document}

Answer 1

Some small mistakes you have done:

• If you set \newbool{myBool} and \newcounter{rownum} inside the definition of the command \buildrows, the commands will be defined every time you call the command \buildrows. So the definition must be done before.
• The command \whileboolexpr doesn't accept a single bool. The first argument of whileboolexpr evaluates the first argument. This is described in section 3.6.5 of the documentation.
• This is really a tip: Instead of using \expandafter you can use the command \csdef provided by etoolbox.

Here a complete MWE

\documentclass{report}
\usepackage{xparse}
\usepackage{etoolbox}

\newcounter{RoomCount}
\NewDocumentCommand\Room{+R(){TBA}}{%
 \stepcounter{RoomCount}%
 \csdef{Room\theRoomCount}{#1}%
}
\newbool{myBool}%
\newcounter{rownum}%
\setcounter{rownum}{0}
\NewDocumentCommand\buildrows{}{%
 \booltrue{myBool}%
 \whileboolexpr{ bool {myBool} }{%
    \stepcounter{rownum}%
    \ifcsdef{Room\therownum}%
    {\csname Room\therownum\endcsname}%
    {\boolfalse{myBool}}%
 }%
}

\begin{document}
\Room(C244)

\Room(C247)

\begin{tabular}{l}
\buildrows{}
\end{tabular}

\buildrows{}
\end{document}