TikZ cycle through foreach

Question

Dears,

I am facing the following problem. Given a set of points, I have to draw the geometric shape of these points, however, I have to do this programmatically. Take a look at this MWE.

\documentclass{beamer}

\usepackage{tikz}

\begin{document}
    \begin{frame}
        \begin{figure}
            \begin{tikzpicture}
                % nodes
                \coordinate (a) at (0, 0);
                \coordinate (b) at (1, 0);
                \coordinate (c) at (1, 1);
                \coordinate (d) at (0, 1);

                % block
                \def\blockA{a, b, c, d}

                % draw cycle
                % - static way
                \draw[fill=gray!50, draw = white] (a) -- (b) -- (c) -- (d) -- cycle;

                % - desired way
                \foreach \v [count=\i] in \blockA {
                    % ...
                }
            \end{tikzpicture}
        \end{figure}
    \end{frame}
\end{document}

I need to find proper ways to implement the % - desired way. I would like to know if anyone has ever worked with this. If anyone has any questions or suggestions, please feel free to let me know.

Thank you and best regards.

Answer 1

The simplest way I can think of is

\draw [fill=red] (a)
\foreach \v [count=\i] in \blockA {
    \ifnum\i>1
        -- (\v)
    \fi
}
-- cycle;

which yields:

since the red fill was done on top of the gray!50.

Code:

\documentclass{beamer}
\usepackage{tikz}

\begin{document}
    \begin{frame}
        \begin{figure}
            \begin{tikzpicture}
                % nodes
                \coordinate (a) at (0, 0);
                \coordinate (b) at (1, 0);
                \coordinate (c) at (1, 1);
                \coordinate (d) at (0, 1);

                % block
                \def\blockA{a, b, c, d}

                % draw cycle
                % - static way
                \draw[fill=gray!50, draw = white] (a) -- (b) -- (c) -- (d) -- cycle;

                % - desired way
                \draw [fill=red] (a)
                \foreach \v [count=\i] in \blockA {
                    \ifnum\i>1
                        -- (\v)
                    \fi
                }
                -- cycle;
            \end{tikzpicture}
        \end{figure}
    \end{frame}
\end{document}