Converting strings to counts

Question

I'm reading in a number (as text) from the aux file and I want to do a numerical test (\ifnum) on it. I can to it using \setcounter and \value, but I really don't want to create a counter just to do a lousy test. Is there a simpler way?

Using pgfmath is not by any stretch of the imagination simpler.

\documentclass{article}
\newcount\test
\newcounter{test}
\begin{document}

\def\temp{1}

\setcounter{test}{\temp}
\ifnum\value{test}>0 Yea!
\else Boo!
\fi

\test=\temp
\ifnum\test>0 Yea!
\else Boo!
\fi

\end{document}

In retrospect, my mistake is obvious. In an expression like

\test=1

the end-of-line terminates both adding digits and conversion of "1" to a count. But with

\test=\temp

the end-of-line is consumed terminating the macro name. I suspect that the final expansion of this is actually

\test=1 Boo!

which is legal but too late. The simplest solution

\test=\temp\relax

uses \relax to force the expression to completion.

How about \ifnum\temp>0...? Additionally, if you need to operate on the variable, you can use a \numexpr as in \ifnum\numexpr\temp-2\relax>0... — Steven B. Segletes, Dec 16 '14 at 20:23
You could check into using etoolbox which provides a host of numeric comparison functions. — Werner, Dec 16 '14 at 20:34
Actually, all I needed to do was use \test=\temp\relax. This also works for dimens. — John Kormylo, Dec 17 '14 at 02:16
@JohnKormylo: The question itself doesn't have anything to do with \relax, nor would people benefit from such a tag for this question. — Werner, Jan 01 '15 at 20:16
It is a somewhat undocumented application. See also http://tex.stackexchange.com/questions/96501/what-does-relax-do — John Kormylo, Jan 02 '15 at 15:14
egreg impressed upon me (long ago) the prudence in ending a length (and I suppose count) assignment with \relax to close out the operation. — Steven B. Segletes, Jan 07 '15 at 21:06

Steven B. Segletes · Accepted Answer · 2014-12-17T02:05:10.460

5

As I indicated in my comment, you can dispense with the counters. Just use the \def as an argument. If you need a more complex calculation, you can use \numexpr, as in my 2nd example.

\documentclass{article}
\begin{document}

\def\temp{1}
\def\X{2}

\ifnum\temp>0 Yea!
\else Boo!
\fi

\ifnum\numexpr\temp-\X\relax>0 Yea!
\else Boo!
\fi

\end{document}

enter image description here

To follow up with the OP's comment about difficulty of mixing tokens and counters, I will post this MWE that works with that mix:

\documentclass{article}
\newcounter{mycount}
\setcounter{mycount}{0}
\begin{document}
\def\temp{1}
\ifnum\value{mycount}>\temp Yea!
\else Boo!
\fi
\end{document}

edited Dec 17 '14 at 02:05

answered Dec 16 '14 at 20:30

Steven B. Segletes

237,551

\numexpr is what I was looking for, but most surprising was that you can use \ifnum to compare two strings or two counts, but not a string and a count. – John Kormylo Dec 17 '14 at 01:30
@JohnKormylo You can do \newcounter{mycount}\setcounter{mycount}{0}\ifnum\themycount>\temp... or \ifnum\value{mycount}>\temp... – Steven B. Segletes Dec 17 '14 at 01:38
\ifnum\value{mycount}>\temp doesn't work, or at least I've been having problems with it all day. – John Kormylo Dec 17 '14 at 01:55
@JohnKormylo Well I noticed your MWE had \newcount\test, rather that \newcounter{test}. Perhaps that could account for it. I tested my comment before posting. Please see revision. – Steven B. Segletes Dec 17 '14 at 02:01
Actually, I had both (\c@test does not conflict with \test). Anyway, it looks like my problem was due to something else altogether, and I may wind up deleting this question as irrelevant. – John Kormylo Dec 17 '14 at 02:08

Converting strings to counts

1 Answers1