How do I typeset the c++ increment symbol in LaTeX?

Question

How can I typeset the increment "+=" symbol? It should act as a relation (like =), but should not have extra space between the "+" and "=".

Answer 1

It depends on what you consider right. The first thing to note is that the symbol should represent a relation. TeX puts no space between two consecutive relations (and no line break either). So

\documentclass{article}

\newcommand{\pluseq}{\mathrel{+}=}
\newcommand{\eqplus}{=\mathrel{+}}

\begin{document}
$x\pluseq 2$

$x\eqplus 2$
\end{document}

will produce

If you prefer a (font dependent) negative kerning, just add it; changing the above definitions into

\newcommand{\pluseq}{\mathrel{+}\mathrel{\mkern-2mu}=}
\newcommand{\eqplus}{=\mathrel{\mkern-2mu}\mathrel{+}}

you'd get

Experiment and decide. Having a macro means you can do whatever you want of the symbol, without changing anything in the document body.

Answer 2

Donald Knuth and Silvio Levy's CWEB system uses plain TeX to "pretty-print" C or C++ listings as part of a literate program.

The CWEB macros use \mathrel{+{=}} to typeset this operator. The example below demonstrates how.

---

Take this source file plus.w:

@* Increment operator in \.{CWEB}.

@p
#include<stdio.h>
@#
int main(void)
{
    int x = 2;
    x += 2;
    printf("x + 2 = %d\n", x);
    return(0);
} 

Convert this to a .tex file by running cweave plus, and then typeset that with pdftex plus. You get this typesetting:

So how does CWEB do this in TeX? Look at the generated file plus.tex:

\input cwebmac

\N{1}{1}Increment operator in \.{CWEB}.

\Y\B\8\#\&{include} \.{<stdio.h>}\7
\&{int} \\{main}(\&{void})\1\1\2\2\6
${}\{{}$\1\6
\&{int} \|x${}\K\T{2};{}$\7
${}\|x\MRL{+{\K}}\T{2};{}$\6
${}\\{printf}(\.{"x\ +\ 2\ =\ \%d\\n"},\39\|x);{}$\6
\&{return} (\T{0});\6
\4${}\}{}$\2\par
\fi

\inx
\fin
\con

The relevant line is ${}\|x\MRL{+{\K}}\T{2};{}$\6.

These macros are defined in cwebmac.tex, in the TeXLive distribution (on a standard Linux install it is /usr/local/texlive/2015/texmf-dist/tex/plain/cweb/cwebmac.tex. These two lines are the macros used:

(l. 85) \def\MRL#1{\mathrel{\let\K==#1}} 

(l. 308) \let\K== % assignment operator 

So the program uses \MRL{+\K} for +=, and that expands first to \mathrel{\let\K== +{\K}}, then finally to \mathrel{+{=}}.

Therefore, CWEB uses \mathrel{+{=}}, QED.

Answer 3

Use \mathrel{+=} to get the spacing right.

Answer 4

minted or listings should be used when displaying code. See How to print Source Code with LaTeX.

If you only have a single line, I would prefer egregs solution. But that's totally personal preference. As he said, if you use a macro you can easily change that (consistently) in your document. Just try what you like most.

minted

The example from Andrew Cashner looks like this when printed with minted:

LaTeX source:

\documentclass[a4paper,12pt]{article}
\usepackage{amssymb} % needed for math
\usepackage{amsmath} % needed for math
\usepackage[utf8]{inputenc} % this is needed for german umlauts
\usepackage[ngerman]{babel} % this is needed for german umlauts
\usepackage[T1]{fontenc}    % this is needed for correct output of umlauts in pdf
\usepackage[margin=2cm]{geometry} %layout
\usepackage{minted} % needed for the inclusion of source code

\begin{document}
\section{Increment operator}

\inputminted[numbersep=5pt, tabsize=4, frame=none, label=main.c]{c}{main.c}

\end{document}

Source file main.c:

#include<stdio.h>

int main(void)
{
    int x = 2;
    x += 2;
    printf("x + 2 = %d\n", x);
    return(0);
}

Compiled with pdflatex -shell-escape $(SOURCE).tex -output-format=pdf.

Answer 5

Adjust the manual spacing in the \hspace to your taste.

\documentclass{article}

\newcommand{\plusequals}{\mathrel{\mathord{+}\hspace*{-1pt}\mathord{=}}}

\begin{document}
$x \plusequals y$

$x = y$

$x + y$
\end{document}