\pgfmath and \foreach in TikZ

Question

I am quite new to TikZ. I have the following code:

\documentclass{article} 
\usepackage{tikz}
\usetikzlibrary{chains}
\begin{document}
\begin{tikzpicture}[start chain=circle placed {at=(\tikzchaincount*30:1.5)},
                    regular/.style={draw,circle,inner sep=0,minimum size=4mm}]
\foreach \i in {0,...,11}
  \node [on chain, regular] (\i) {\i};
\foreach \i in {0,...,11}
  \draw [->] (\i) to ({\pgfmathparse{int(mod(\i+1,12))}\pgfmathresult});
\end{tikzpicture}
\end{document}

What I intended to do is to draw a series of 12 nodes evenly placed on a circle, and draw an arrow between every two neighbors. LaTeX gave an error message saying

!incomplete \iffalse; all text was ignored after ...

What is the correct way to do what I intended?

That's not the only error I get. The first one I get has to do with \tikzchaincount which doesn't seem to be defined... — jub0bs, Oct 29 '13 at 10:52
One problem might be the missing space between circled placed{at: that should be circled placed {at I think. — Claudio Fiandrino, Oct 29 '13 at 10:54
@Jubobs, thanks for pointing out the missed space. I must have accidentally deleted the space while formatting the code for here. — wdg, Oct 29 '13 at 11:00
This has been discussed on TeX.sx before: Numbering nodes in a for loop and How to draw a circle whose radius is a multiple of the distance of two points in TikZ? and Computing value using pgfmath for use in coordinates? — Qrrbrbirlbel, Oct 29 '13 at 12:59

score 18 · Accepted Answer · answered Oct 29 '13 at 11:04

When using macros in node names, the macros have to be expandable in an \edef context. \pgfmathparse is not. So you need to do the computation beforehand and only use the result of it in the node name. One way is to use the evaluate key on the \foreach as in the following.

\documentclass{article}
%\url{http://tex.stackexchange.com/q/141259/86}
\usepackage{tikz}
\usetikzlibrary{chains}
\begin{document}
\begin{tikzpicture}[start chain=circle placed {at=(\tikzchaincount*30:1.5)},regular/.style={draw,circle,inner sep=0,minimum size=4mm}]
\foreach \i in {0,...,11}
  \node [on chain, regular] (\i) {\i};
\foreach[evaluate=\i as \ni using {int(mod(\i+1,12))}] \i in {0,...,11}
  \draw [->] (\i) to (\ni);
\end{tikzpicture}
\end{document}

circular nodes

kiss my armpit · Answer 2 · 2013-10-29T12:34:32.397

\documentclass[pstricks]{standalone}
\usepackage{pst-node,pst-plot}

\begin{document}
\begin{pspicture}[arrows=->,radius=12pt](-3,-3)(3,3)
    \curvepnodes[plotpoints=13]{0}{360}{2.5 t 90 add PtoC}{P}% 90 is an angular offset
    \multido{\i=0+1}{\Pnodecount}{\Cnodeput(P\i){A\i}{\i}}
    \Cnodeput(P\Pnodecount){A\Pnodecount}{}
    \multido{\ix=0+1,\iy=1+1}{\Pnodecount}{\ncline{A\ix}{A\iy}}
\end{pspicture}
\end{document}

enter image description here

Animation

\documentclass[pstricks]{standalone}
\usepackage{pst-node,pst-plot}

\begin{document}
\multido{\iN=4+1}{10}{%
\begin{pspicture}[arrows=->,radius=12pt](-3,-3)(3,3)
    \curvepnodes[plotpoints=\iN]{0}{360}{2.5 t 90 add PtoC}{P}% 90 is an angular offset
    \multido{\i=0+1}{\Pnodecount}{\Cnodeput(P\i){A\i}{\i}}
    \Cnodeput(P\Pnodecount){A\Pnodecount}{}
    \multido{\ix=0+1,\iy=1+1}{\Pnodecount}{\ncline{A\ix}{A\iy}}
\end{pspicture}}
\end{document}

enter image description here

curvepnodes is defined in pst-node while plotpoints is defined in pst-plot. We have to load both packages when using curvepnodes, is it funny? — kiss my armpit, Oct 29 '13 at 12:42

\pgfmath and \foreach in TikZ

2 Answers2

Animation

Linked