Mdthbs

I would like to understand the difference between the and value{}
when using counters in LaTeX.

thecounter typesets the result of the counter, be it in arabic, roman, etc, while value{counter} provides an integer value in return. In many, but not all, instances, the difference will go unnoticed.

The rule is, if you are looking for a character, use the...; if you are looking for an integer, use value{...}.

Here's an example where it matters. By typesetting the page number in roman (via pagenumbering{roman}), the option of romannumeralthepage is no longer an option, since it would be attempting romannumeral i, whereas romannumeralvalue{page} works fine.

documentclass{article}

pagenumbering{roman}

begin{document}

romannumeralvalue{page}



% romannumeralthepage will break

end{document}

Here's another example...you cannot typeset value

documentclass{article}

begin{document}



newcounter{Q}

setcounter{Q}{2}



%value{Q} will break



theQ

end{document}

The difference can also affect comparisons, since if compares tokens, not integers:

documentclass{article}

begin{document}



newcounter{Q}

setcounter{Q}{2}



ifvalue{Q}2 Telse Ffi is false



iftheQ2 Telse Ffi is true



end{document}

The above example would show a match, were the ifs changed to ifnums, since ifnum will interpret/convert the character 2 into an integer. However, even that can get you into trouble for more complex cases.

Here, I can combine theQ with 3 to represent 23. The same does not apply for value{Q}3.

documentclass{article}

begin{document}



newcounter{Q}

setcounter{Q}{2}



%ifnumvalue{Q}3=23 Telse Ffi will break



ifnumtheQ3=23 Telse Ffi is true



end{document}

This is an interesting mathematical question. The number two hundred seventy-five can be represented in different ways:

• 275 in decimal notation with “Western digits”,


• ٢٧٥ in decimal notation with “Arabic digits”,


• CCLXXV in Roman numerals,


• 113 in hexadecimal digits,


• 100010011 in binary digits,

and many others (it's duecentosettantacinque in Italian).

When you define a new counter in LaTeX, with newcounter{foo}, also the command thefoo is defined, which will expand to a representation of the value stored in the counter; the command is initialized to provide the decimal representation of the counter, but one can say

renewcommand{thefoo}{roman{foo}}

and thereupon, calling thefoo when the counter stores the number 275 will produce

cclxxv

(after macro expansion). The initial definition is essentially equivalent to

newcommand{thefoo}{arabic{foo}}

A common case is the counter page: in the class book, the counter's representation uses roman in the front matter and arabic in the main matter and back matter.

However, the number stored in foo is indepedent of its representation: in some sense, the counter stores the abstract number, something not especially tied to a representation thereof. This abstract value is accessed to by value{foo}.

Let's say you have an application where a counter is bound to contain only the values from 0 to 3 and you want to represent these values with non numerical objects; you can define, for instance,

renewcommand{thefoo}{%

  ifcasevalue{foo}%

     apple% case 0

  or

     orange% case 1

  or

     apricot% case 2

  or

     strawberry% case 3

  else

     bummer% wrong setting found

  fi

}

The conditional ifcase branches according to the number following it, in this case the abstract value stored in the counter.

You cannot say value{foo} in the document in order to print the value, because the abstract number can only be represented in some way and you have to specify which one. Instead, when TeX is looking for a number (such as after ifcase), then value{foo} is the right code to use.

The objection “but we could use arabic{foo} instead of value{foo}” is dismissed. You really want the abstract number there, not some representation thereof.