So, I've got this command that I use to format variable names in my homework:
\newcommand*{\var}[1]{\ensuremath{\mathord{\mathtt{#1}}}}
The problem is that it doesn't handle subscripts smoothly. I end up typing this frequently:
\var{Something}_{\var{SomethingElese}}
Which is a bit cumbersome. Can I make it work with:
\var{Something_SomethingElse}
or at least:
\var{Something}_\var{SomethingElse}
You must enclose the subscript in a brace/group to indicate the scope it. Therefore, using
\newcommand*{\var}[1]{$\mathtt{#1}$}
is sufficient:
\documentclass{article}
\newcommand*{\var}[1]{$\mathtt{#1}$}
\begin{document}
\var{Something_{SomethingElse}}
\end{document}
Just using the definition
\newcommand*\var[1]{\mathtt{#1}}
will allow you to blithely apply subscripts without braces as in $\var{XYZ}_\var{ABC}$. Placing the whole thing in \mathord has the effect of making the contents immune to font family changes, but if you don't have a good reason for wanting this, I question whether it's a priority over the ease of use you do request.
I also suggest you remove \ensuremath; for one, it breaks braceless subscripts. In general I feel that it is undesirable to hide the "mathiness" of a formula even if it saves a little writing when you can (sometimes! And not when you're using subscripts) avoid writing $...$. See this question for a discussion.
The trick for subscripts is to define \var in such a way, that it expands to a subformula. This is achieved by an additional pair of curly braces. I have removed \mathord, because it is not needed. \mathtt also puts its argument into a subformula and subformulas are already "mathord".
\documentclass{article}
\newcommand*{\var}[1]{{\ensuremath{\mathtt{#1}}}}
\begin{document}
Variable \var{foo} and as subscript for \var{bar}: $\var{bar}_\var{foo}$
Another example: $X_\var{foo}^\var{bar}$
\end{document}
This works, because subscript and superscript do not look for arguments, but for a math atom, a subfomula in this case.
