# How to align comments in algorithm code?

I will to align comments in another column, package algorithm. (Similar question: Faulty right alignment for comments in algorithmic package), but I will to become that result:

\usepackage{algorithm,algorithmic}
\renewcommand{\algorithmiccomment}[1]{\bgroup\hfill//~#1\egroup}

[...]

\begin{algorithm}
\caption{$function(n : \mathbb{N}_0) : \mathbb{N}_0$}
\label{algo1}
\begin{algorithmic}[1]
\REQUIRE $n \in \mathbb{N}_0$
\STATE $result \leftarrow 0 : \mathbb{N}_0$
\STATE $temp \leftarrow 1 : \mathbb{N}_0$
\FOR[$n$ Durchläufe]{$i \leftarrow 0$ \TO $n-1$}
\FOR{$j \leftarrow i$ \TO $i$}
\STATE $temp \leftarrow temp \cdot 2$ \COMMENT{Multiplikation}
\ENDFOR
\STATE $result \leftarrow result + temp$ \COMMENT{Addition}
\STATE $temp \leftarrow 1$
\ENDFOR
\RETURN $result$
\end{algorithmic}
\end{algorithm}

• Please always supply a complete (\documentclass to \end{document}) example document that demonstrates the problem and allows people to test their answers. Commented May 24, 2014 at 22:19

Here is an algorithmicx implementation:

\documentclass{article}
\usepackage[utf8]{inputenc}
\usepackage{algorithm,algcompatible,amssymb,amsmath}
\renewcommand{\COMMENT}[2][.5\linewidth]{%
\leavevmode\hfill\makebox[#1][l]{//~#2}}
\algnewcommand\algorithmicto{\textbf{to}}
\algnewcommand\RETURN{\State \textbf{return} }
\begin{document}

\begin{algorithm}
\caption{$\text{function}(n : \mathbb{N}_0) : \mathbb{N}_0$}\label{algo1}
\begin{algorithmic}[1]
\REQUIRE $n \in \mathbb{N}_0$
\STATE $\text{result} \leftarrow 0 : \mathbb{N}_0$
\STATE $\text{temp} \leftarrow 1 : \mathbb{N}_0$
\FOR{$i \leftarrow 0$ \algorithmicto{} $n-1$} \COMMENT{$n$ Durchläufe}
\FOR{$j \leftarrow i$ \algorithmicto{} $i$}
\STATE $\text{temp} \leftarrow \text{temp} \cdot 2$ \COMMENT{Multiplikation}
\ENDFOR
\STATE $\text{result} \leftarrow \text{result} + \text{temp}$ \COMMENT{Addition}
\STATE $\text{temp} \leftarrow 1$
\ENDFOR
\RETURN $\text{result}$
\end{algorithmic}
\end{algorithm}
\end{document}


\COMMENT[<len>]{<stuff>} is reformatted to put the comment <stuff> in a box of width <len> (default is .5\linewidth) flush right. You can adjust this to your liking.

A pure algorithmic implementation is somewhat different:

\usepackage{letltxmacro}

\newlength{\commentindent}
\setlength{\commentindent}{.5\textwidth}
\makeatletter
\renewcommand{\algorithmiccomment}[1]{\unskip\hfill\makebox[\commentindent][l]{//~#1}\par}
\LetLtxMacro{\oldalgorithmic}{\algorithmic}
\renewcommand{\algorithmic}[1][0]{%
\oldalgorithmic[#1]%
\renewcommand{\ALC@com}[1]{%
\ifnum\pdfstrcmp{##1}{default}=0\else\algorithmiccomment{##1}\fi}%
}
\makeatother


It uses e-TeX (for the string comparison), but that can be changed. The reason for the difference in implementation is mainly because of the way loops are handled in algorithmic - the comment is inserted as an optional argument to the loop structure. As such, it's difficult to allow another optional argument for the length parameter as above in the algorithmicx implementation. The work-around is to define a length \commentindent that handles this in a similar way the optional argument would handle things.

Here's a full implementation, with the same output:

\documentclass{article}
\usepackage[utf8]{inputenc}
\usepackage{algorithm,algorithmic,amssymb,amsmath,letltxmacro}
\newlength{\commentindent}
\setlength{\commentindent}{.5\textwidth}
\makeatletter
\renewcommand{\algorithmiccomment}[1]{\unskip\hfill\makebox[\commentindent][l]{//~#1}\par}
\LetLtxMacro{\oldalgorithmic}{\algorithmic}
\renewcommand{\algorithmic}[1][0]{%
\oldalgorithmic[#1]%
\renewcommand{\ALC@com}[1]{%
\ifnum\pdfstrcmp{##1}{default}=0\else\algorithmiccomment{##1}\fi}%
}
\makeatother

\begin{document}

\begin{algorithm}
\caption{$\text{function}(n : \mathbb{N}_0) : \mathbb{N}_0$}\label{algo1}
\begin{algorithmic}[1]
\REQUIRE $n \in \mathbb{N}_0$
\STATE $\text{result} \leftarrow 0 : \mathbb{N}_0$
\STATE $\text{temp} \leftarrow 1 : \mathbb{N}_0$
\FOR[$n$ Durchläufe]{$i \leftarrow 0$ \TO $n-1$}
\FOR{$j \leftarrow i$ \TO $i$}
\STATE $\text{temp} \leftarrow \text{temp} \cdot 2$ \COMMENT{Multiplikation}
\ENDFOR
\STATE $\text{result} \leftarrow \text{result} + \text{temp}$ \COMMENT{Addition}
\STATE $\text{temp} \leftarrow 1$
\ENDFOR
\RETURN $\text{result}$
\end{algorithmic}
\end{algorithm}
\end{document}

• Not sure if this is some change in algorithmicx, but I had to renew \algorithmiccomment instead of \COMMENT. Commented Jun 14, 2023 at 19:17
• @paleonix: Then you're probably also using \algorithmiccomment in your code, not \COMMENT.
– Werner
Commented Jun 14, 2023 at 19:25
• I'm using \Comment. Commented Jun 15, 2023 at 10:31
• Both \Comment and customization through \algorithmiccomment are documented (page 4). Like I said, this might have changed since 2014. Commented Jun 15, 2023 at 10:34