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Questions tagged [conditionals]

{conditionals} is about macros like \if and \ifx that may execute other macros depending on whether certain conditions are true or not. Popular packages are {etoolbox} and {ifthen}.

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245
votes
4answers
146k views

LaTeX conditional expression

I would like to be able to set a flag at the beginning of the main flag (say output) that tells if I want to produce a paper document or an electronic document. Then I should check this flag to ...
100
votes
4answers
145k views

Large braces for specifying values of variables by condition

How do I typeset something like, X = 0 if a=1, 1 otherwise, using those huge left braces and specifying each condition in a line?
95
votes
4answers
36k views

Why is the ifthen package obsolete?

In the LaTeX companion, the authors recommend to use the package ifthen for complex conditional. But in his answer to LaTeX conditional expression Will Robertson doesn't mention it, and in the ...
90
votes
4answers
33k views

How to check if a macro value is empty or will not create text with plain TeX conditionals?

I have a macro which holds some text value, e.g. \macro{some text}. If it is empty, I would like for nothing to appear in the document, but it has some content of any kind which would produce text ...
87
votes
6answers
6k views

Which document class is being used?

Is there a way to programmatically determine which document class is in effect? I'd like to be able to write conditional macros that behave differently depending on which document class is currently ...
83
votes
7answers
30k views

Conditional typesetting / build

Let's say I have .tex file which is a set of problems and solutions, of which I want to make two pdf files, one which includes the solutions and one which doesn't. so I need to build the .tex file ...
77
votes
3answers
25k views

Difference between \if and \ifx

I try to understand the subtleties of TeX programming, but it is not always easy. For example, in the following code : \def\first{abc} \def\second{abc} \ifx\first\second OK!\else false \fi I ...
62
votes
3answers
9k views

Understanding \@ifnextchar

I understand the definitions of the \makeatletter and \makeatother commands and also \def and \newcommand somewhat. But, explained in a simple way, what is happening in the following line? \@...
57
votes
2answers
13k views

What does \ifx\\#1\\ stand for?

The following usage of \ifx can be found in several packages and also in answers on this site. What does this syntax exactly mean? Are there any alternatives and drawbacks? \newcommand{\mycommand}[2][...
57
votes
1answer
11k views

Test if a package (or package option) is loaded

[french]{babel} (aka frenchb) is incompatible with some other packages, such as tikz, since it tries to insert \thinspace before semi-colons. In order to make these two play nice, you have to call \...
56
votes
6answers
23k views

If Then Else for odd page/even page

How to use if-then-else structure in LaTeX? I need an example of odd and even page. if odd then command 1 else command 2
56
votes
4answers
18k views

How to form “if … or … then” conditionals in TeX?

I feel really stupid for asking this, but how do you form more complex if conditionals in TeX? I'm looking for something like: \ifnum\x=1 OR \ifnum\x=14 {do this} \else {do that} \fi I don't ...
51
votes
2answers
47k views

Conditionally hidden slides in beamer

When creating a presentation, I sometimes create extra slides that contain additional information, a more thorough explanation, or an extra plot pertaining to certain parts of my talk. These extra ...
49
votes
4answers
17k views

How can I check in LaTeX (or plain TeX) whether a command exists, by name?

I'm looking for a LaTeX way to control macro expansion, contingent on some macro being defined or not. I'm looking for something like this (but then actually working): \newcommand[1]{\checkfor}{ \...
45
votes
4answers
19k views

How to conditionally define a new command in LaTeX?

I'm trying to compile a LaTeX code with an older version of some package. Thus, I'm having a few issues due to undefined commands. How can I add conditional code so that I can define some work-around ...
45
votes
6answers
10k views

Is it possible to keep my translation together with original text?

I have an English article in LaTeX, which I'm going to translate to Russian. I want to keep my translation in sync with the original text. It means that I want every paragraph to stay as close to its ...
44
votes
5answers
22k views

new command with cases / conditionals / 'if… then's

Suppose I want to define a command, say, \tree with, say, two arguments. I would like \tree to do different things depending on what my first argument is. For example, if #1 = a, then return $\sqrt{#...
44
votes
1answer
14k views

Can I test if a file exists? [duplicate]

Can I somehow test if a file exists? And can I use this to do only things when it exists? I like to do something like if(exist('members.csv')) { do something }
43
votes
3answers
8k views

Use “default” figure if file is missing?

I was recently in charge of organizing all of the references and labels in a very large scientific proposal document. My workflow typically involved compiling the document, seeing a "There were ...
41
votes
2answers
5k views

Opposite of \ensuremath: ensure that I'm *not* in math mode?

I'd like a macro that is the opposite of \ensuremath: something like \ensurenotmath, which makes sure that its argument is not typeset in math mode. Is there such a macro, or a way to implement it? ...
39
votes
5answers
7k views

Parametrize shading in table through TikZ

I wanted to do some shading in a table according to its values. For example, if you see the table below: a b c d a 90 10 0 0 b 0 80 10 10 c 0 0 95 5 d 0 10 5 85 I want to shade ...
39
votes
1answer
1k views

How can I know if a node is already defined?

I think I've seen this question before, but I can't find it. The problem is simple; before I assign a name to a node I would like to know if the name is already used. I think when a node is created \...
39
votes
1answer
777 views

Test if paragraph has an overfull line

I'd like to test if the last paragraph has any overfull line. The naive approach of looking at the \badness once the paragraph is finished does not work, as it will only give the badness of the last ...
38
votes
3answers
12k views

When to use @ in an \if statement

I am new to LaTeX and so this question might come across as rather basic. It might also reflect my biases/assumptions from my C/C++ programming days. I was seeing the code of the 'exam' class and ...
36
votes
3answers
10k views

Includegraphics maximum width

With \includegraphics I can give the width of the resulting image (which would be scaled). How can I give a maximum width of the image? That is, if the original is smaller than X, I'd like to keep ...
32
votes
6answers
32k views

What is \iffalse for?

So this is something I've wondered about for a while. What use is a conditional that always evaluates to false? I guess it's a neat way to "hide code from LaTeX" but apart from that, is it ever useful?...
32
votes
6answers
5k views

Testing for number

How do I test if a given parameter is a number, in order to apply a different style? And if not, just ignore... Like: \domorestuffifnumber{things} -> things \domorestuffifnumber{123} -> \...
32
votes
6answers
3k views

Redundancy in bib file: conditionally suppress url if same as doi?

Mathscinet gives bibtex entries with both a doi and a url field included. Typically they look something like @article {some-article, […] DOI = {10.1016/j.apal.2008.12.003}, URL = {http://dx....
31
votes
5answers
3k views

Combining \ifxetex and \ifluatex with the logical OR operation

I want to write in the preamble of a LaTeX document code that should be take into account by different compilers when the document is typeset. There are fragments that should be used: only by xelatex ...
31
votes
4answers
2k views

Alternate he / she in text

This question led to a new package: he-she I have seen a book that instead of using the masculine pronoun (he, his, etc.) alternates the gender ('he' then 'she' then next time 'he' again). Is ...
31
votes
3answers
7k views

Hide custom environment content based on boolean

I have a custom environment which adds some text around its content, but I also want it to be able to show or hide its contents depending on a boolean. I have tried doing the following: \newif\...
31
votes
1answer
2k views

Use of \relax after \ifnum … \fi construction

I'm reading Malcolm Clark's A Plain TeX Primer. On page 111 there's an exercise to define a macro that prints the current time. I've reproduced Clark's answer below: \newcount\minleft \newcount\...
30
votes
6answers
9k views

Test whether token list is empty

Is it possible to test whether a token list register is empty without expanding it?
30
votes
4answers
4k views

On testing two fully expanded character strings for equality

I know three macros that test two fully expanded character strings for equality: \ifthenelse{\equal{<op1>}{<op2>}}{<true>}{<false>} (ifthen package) \IfStrEq{<op1>}{<...
30
votes
2answers
5k views

What does \begingroup\expandafter…\endgroup do?

I often see code of the following form in package implementations (this example is from the LaTeX3 sources): \begingroup\expandafter\expandafter\expandafter\endgroup \expandafter\ifx\csname directlua\...
29
votes
3answers
8k views

What is the difference between \ifx\somecommand\undefined and \ifdefined\somecommand\else?

What is the difference between \ifx\cyrdash\undefined and \ifdefined\cyrdash\else? \cyrdash is any macro.
29
votes
5answers
3k views

Detect beginning of a sentence in a macro for capitalization

Is it possible to make macros give different results at the beginning of a new sentence? Suppose that I want the macro "\secname" to write "Section" at the beginning of a new sentence, and "section" ...
28
votes
2answers
5k views

Doing something only when the draft option is on?

I would like to do some stuff that is only enabled when the draft option is given in \documentclass[draft]{article}. How would I go about doing this?
28
votes
3answers
6k views

How to check if the value of a parameter is a number?

I have a command with a parameter. I want to check if its value is a positive number and perform actions based on that. \newcommand{\mycommand}[1]{ \ifnum#1>0% %some actions \fi } ...
28
votes
2answers
7k views

Difference between \newbool and \newtoggle from etoolbox package

Paul Gaborit's answer to How to detect if option provided via \tikzset uses \newbool to define a new boolean \booltrue to set a boolean, and \ifbool to perform a conditional operation all from the ...
28
votes
2answers
24k views

Variables for hiding or showing text in Latex

I would like to have some variables for showing or hiding text in Latex. For example, I would like to have two versions of a document. A short version and a long version by changing a variable at the ...
28
votes
4answers
2k views

Test success of write18

For the new version of my package and class standalone I like to call external programs: further (pdf)latex runs to optionally compile included standalone files, and to convert the resulting PDF to ...
27
votes
5answers
3k views

How I can automatically add a page if the total number of pages is odd?

I need automatically add a blank page (also without document header, numbering and footer) at the end of the document, if the total numbers of pages is odd. How I can do that? And preferably without ...
27
votes
1answer
3k views

Check if next char is {

Using \@ifnextchar one can detect if e.g. the next Character is a [, e.g.: \@ifnextchar[% { %% code to execute if [ scanned. }{ %% code to execute if [ scanned. } However, I can’t seem to ...
26
votes
7answers
13k views

Implementing switch cases

I'd like to have command built around a switch-case environment in LaTeX, much like the example below: \documentclass{article} \usepackage{xstring} \newcommand{\dothis}[1]{% \IfStrEqCase{#1}{{a}{so ...
26
votes
3answers
581 views

Is it possible to define an acronym-command which behaves differently on the first invocation than on the rest?

Most technical writers will immediately see how I'd like to use this. I'm writing a paper about something I'll call That Which Will Be Abbreviated (TWWBA). I'd like to have a macro, \TWWBA{}, that ...
26
votes
3answers
7k views

Check if a string contains a given character

I want to implement an if-then-else depending on whether the argument contains a special character or not. Should I be looking here: http://www.tug.org/TUGboat/Articles/tb28-1/tb88glister.pdf, or does ...
25
votes
2answers
5k views

How can I test for the current font?

The situation is the following, I have one font a with one feature and another font b with another feature and I am writing a command that if the current font is a need to switch to font b but if the ...
25
votes
1answer
1k views

What is an \if?

I'm reading TeX by Topic, but in little chunks (rather than from first page to last) and just read the stuff on conditionals. I want to be sure that I understand what's going on when TeX starts ...
24
votes
2answers
12k views

Conditional cases expression

How can I create a command \if with 1 argument, namely #1, \if{#1=1}{symbol1}...{#1=n}{symboln} that returns symbol1, when #1 is 1, ..., and returns symboln, when #1 is n, and returns nothing, when ...