[Tex/LaTex] the difference between \number and \the

macros

I am trying to learn more about macro programming – if that's the right word – in TeX and LaTeX. I began by defining a quantity I called Sum : \newcount\Sum. I then wrote \Sum=0. Then I did some arithmetical operations on Sum, by using \multiply . . . by . . . and \advance . . . by . . ..

Finally I wanted to print out (in the document) the value of Sum. For that I used the line

 The Sum equals **\number**\Sum ,

and it worked as expected ! But later on, I discovered that I might just as well have written

The Sum equals **\the**\Sum ".

And now I wonder which of the two is the preferred way to write out a numerical value. Are they equivalent ? Or are they intended for different purposes – even if the results overlap in my example ?

Here is an MWE:

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%%
%% Here is the example tex-file that illustrates use of \number and \the .   
%%                                           
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%       

\documentclass{article}
\usepackage[paperwidth=4in, paperheight=0.8in]{geometry}

\begin{document}

\newcount\a  \newcount\b  \newcount\Sum

\a=1   \b=5  \Sum=0
\advance\Sum by \a  \multiply\Sum by \b
\advance\Sum by \a  \multiply\Sum by \b

\noindent
The Sum equals \number\Sum  \quad;\quad I used ``number''.
\par \vskip 10pt \noindent
The Sum equals \the\Sum     \quad;\quad I used ``the''.

\end{document}

Best Answer

\number and \the are similar on a count register. \the may be applied to more types, such as

\the\dimen0

\the\everypar

 \the\font

Using \number on those cases is either an error or (in the first case) casts the dimen to a number, taking its value is sp units.

Related Solutions

[Tex/LaTex] the difference between \let and \def

The difference is in the time at which the ‘right hand side’ is evaluated.

Thus \let\foo\bar defines \foo to have the value that \bar had at the point of definition. On the other hand, \def\foo{\bar} in effect defines \foo to have the value that \bar has at the point of use.

Consider:

\def\bar{hello}
\let\fooi\bar
\def\fooii{\bar}
\fooi +\fooii

\def\bar{goodbye}
\fooi +\fooii

This produces

hello+hello
hello+goodbye

This is a simple process.

However it's also a subtle one, so it might be worth highlighting a few key points:

When TeX encounters control sequences such as \fooi, it evaluates them; if these are macros (that is, they have been defined by \def, or \let equal to something which was defined by \def), then the result is that they will expand to other tokens, which TeX will then examine in turn, and so on, recursively, until what's left is either ‘primitive’ control sequences or letters (I'm simplifying a little bit).
\fooi expands directly to the characters hello (because \bar initially did, and \fooi was defined to have the same value).
\fooii, in contrast, expands to \bar, which is then immediately reexamined and reexpanded. In the first case, \bar expands to hello and in the second case to goodbye. The definition of \fooii hasn't changed, but \bar has been redefined in between.
Getting a clear idea of the process of this recursive expansion is very helpful when learning how to develop and debug TeX macros.

[Tex/LaTex] the difference between \def and \newcommand

\def is a TeX primitive, \newcommand is a LaTeX overlay on top of \def. The most obvious benefits of \newcommand over \def are:

\newcommand checks whether or not the command already exists
\newcommand allows you to define an optional argument

In general, anything that \newcommand does can be done by \def, but it usually involves a little trickery and unless you want something that \newcommand can't do, there's no point in reinventing the wheel.

In answer to your particular points:

Yes and No. A command defined using \def has to know exactly what its options are, and how they will be presented to it. However, a TeX command can be a bit clever and examine things other than its arguments. The way that optional commands are handled is to look at the next character in the stream and if it is [ then one version of the command is called, whereas if it isn't then another is called. So if you're prepared to do some hackery, then optional arguments are possible via \def, but it isn't half so easy as \newcommand.
No. Since \def doesn't check for a command already being defined, you can redefine stuff simply using \def again. To get the checking, you need to use the \@ifundefined command (note the ampersat (@) sign!).
No!

There's probably lots more to be said on the differences, but that's enough from me.

Best Answer

Related Solutions

[Tex/LaTex] the difference between \let and \def

[Tex/LaTex] the difference between \def and \newcommand

Related Question