Mathematical calculation within \foreach loop in tikz

Question

The minimal code below demonstrates the problem. The code as it is does not give the desired output. I assume the \x-\y is not being correctly handled. I have tried including braces, brackets, but to no avail.

\documentclass{article}

\usepackage{tikz}
\usetikzlibrary{calc} 


\newcommand{\connection}[4][]{\draw[{#1}] (#2#3)--([yshift={#4cm}]#2#3) --([yshift={#4cm}]#2#3-|#3#2)--(#2#3-|#3#2)}

\begin{document}

\begin{tikzpicture}

% create the coordinates
\foreach \Lletter/\l in {A/0,B/1,C/2}
    {\foreach \Rletter/\r in {A/0,B/1,C/2}
        {\coordinate (\Lletter\Rletter) at ({\l+\r/10},0);}
}

% create the paths
\foreach \L/\x in {A/5}
{\foreach \R/\y in {A/0,B/1,C/2}
    {\connection{\L}{\R}{\x-\y};}
}

% this is the desired result
% \connection{A}{A}{5};
% \connection{A}{B}{4};
% \connection{A}{C}{3};


\end{tikzpicture}

\end{document}

Answer 1

As touhami said, one way is to include an explicit call to \pgfmathsetmacro within the loop. However, since this is a loop, we might as well use the facilities provided by \foreach itself to evaluate variables using pgfmath expressions.

For example

\documentclass[tikz,border=10pt,multi]{standalone}
\newcommand{\connection}[4][]{%
  \draw [{#1}] (#2#3) -- ([yshift={#4cm}]#2#3) -- ([yshift={#4cm}]#2#3 -| #3#2) -- (#2#3 -| #3#2)
}
\begin{document}
\begin{tikzpicture}
  \foreach \Lletter/\l in {A/0,B/1,C/2}
  {\foreach \Rletter/\r in {A/0,B/1,C/2}
    {\coordinate (\Lletter\Rletter) at ({\l+\r/10},0);}
  }
  \foreach \L/\x in {A/5}
  {\foreach \R/\y [evaluate=\y as \z using {\x-\y}] in {A/0,B/1,C/2}
    {\connection{\L}{\R}{\z};}
  }
\end{tikzpicture}
\end{document}