Array indexing does not work for the node label

Question

There is something I cannot understand. I'm using array indexing and it works for determining the radius of the circles and to positioning the nodes. However it does not work as the node content.

\documentclass{standalone}
\usepackage{color}
\usepackage{tikz}
\usetikzlibrary{calc}
\begin{document}

\begin{tikzpicture}
\def\radi{{1,2,3,4}}
\foreach \x/\a [count=\n] in {0/15,1/345,2/345,3/345}
    \draw[very thin, draw=red!50!white] (0,0) circle [radius={\radi[\x]}] node at (\a:{\radi[\x]}) {{\radi[\x]}};


\end{tikzpicture}
\end{document}

Answer 1

Please don't use color with TikZ!! It already loads xcolor.

Paul Gaborit already gave you the answer that a brace pair doesn't necessarily mean a math operation. Here it is just put inside a text box and TikZ doesn't evaluate it. You can either go parsing the math inside a \pgfextra{...} and use \pgfmathresult or you can explicitly define more variables that use the loop variable via evaluate key.

\documentclass[tikz]{standalone}
\usetikzlibrary{calc}
\begin{document}

\begin{tikzpicture}
\def\radi{{1,2,3,4}}
\foreach \x/\a [
    count=\n,
    evaluate=\x as \myvar using ({\radi[\x]})
    ] in {0/15,1/345,2/345,3/345}
    \draw[very thin, draw=red!50!white] 
        (0,0) circle [radius={\myvar}] 
        node at (\a:{\radi[\x]}) {\myvar};


\end{tikzpicture}
\end{document}