JohnPaul
I copy [this answer](https://tex.stackexchange.com/questions/232039/regular-polygon-and-tkz-euclide) and draw like this


\documentclass [border = 5mm] {standalone}
\usepackage{pgfplots}
\usepackage{tikz}
\usetikzlibrary{shapes.geometric,calc}
\begin{document}
\begin{tikzpicture}[line cap=round,line join=round,c/.style={circle,fill,inner sep=1pt},
,declare function={k=6;}]

\node[regular polygon,regular polygon sides=k,draw,minimum height=5cm] (a) at (0,0) {};
\draw[red] let \p1=($(a.corner 1)-(a.center)$), \n1={veclen(\x1,\y1)} in circle (\n1);
\foreach \x[count=\xi] in {A,B,...,F}{
\node (a-\xi) at ([shift={({90+(\xi-1)*360/6}:3mm)}]a.corner \xi) {$\x$};
}
\pgfmathsetmacro{\k}{k}
\draw[blue] let \p1=($(a.corner 1)-(a.center)$),

\end{tikzpicture}
\end{document}


Can I label A, B, C, ... automatically, not count like this {A,B,...,W}. Sometimes, with n = 8, I count by hand A, B, C, D, E, F, G, H and then {A,B,...,H}.
samcarter
You could use \Alph{<counter>} to show the alphabetic representation of a counter:


\documentclass [border = 5mm] {standalone}
\usepackage{pgfplots}
\usepackage{tikz}
\usetikzlibrary{shapes.geometric,calc}
\newcounter{foo}

\begin{document}
\begin{tikzpicture}[line cap=round,line join=round,c/.style={circle,fill,inner sep=1pt},
,declare function={k=6;}]

\node[regular polygon,regular polygon sides=k,draw,minimum height=5cm] (a) at (0,0) {};
\draw[red] let \p1=($(a.corner 1)-(a.center)$), \n1={veclen(\x1,\y1)} in circle (\n1);
\pgfmathsetmacro{\k}{k}
\foreach \xi in {1,...,\k}{
\setcounter{foo}{\xi}
\node (a-\xi) at ([shift={({90+(\xi-1)*360/\k}:3mm)}]a.corner \xi) {\Alph{foo}};
}
\draw[blue] let \p1=($(a.corner 1)-(a.center)$),

![IMjournal-1.png](/image?hash=571e4cdbd42991df80f7425855f8807483bab3c781a4de924a2feaba3b832d44)