TikZ counter and logical comparison

Question

Does TikZ have counter that is similar to for loop in c language and logical comparison? e.g.,

\foreach \x in {0mm,11.200000mm,...,33.600000mm}
{
  counter++; <== is this possible in tikz
  if(counter == 0) <== is this possible in tikz
    output something
}  

Answer 1

You have a new possibility perhaps interesting for you with pgf 2.1 (or with the last version of pgffor), you can use a new option count. I create two counters \xi and \yi, automatically for each loop you get \xi=\xi+1 etc.

\documentclass{scrartcl}
\usepackage{tikz}
\begin{document}

\begin{tikzpicture}[x=0.75cm,y=0.75cm] 
\foreach \x [count=\xi] in {0,...,6}
{\foreach \y [count=\yi] in {0,...,6}
{\ifnum\xi=\yi 
\node [draw, minimum size=0.666cm] at (\xi,-\yi) {$\infty$}; 
\else
\node [draw, minimum size=0.666cm] at (\xi,-\yi) {$\x\y$};
\fi }}
\end{tikzpicture}
\end{document}

Answer 2

You can use the normal LaTeX counters for that. You can define your own one using \newcounter{name}, set it using \setcounter{name}{value} or add to it using \addtocounter{name}{value}.

You can test counter values using \ifnum 0=\value{name} <true> \else <false> \fi or with the help of the ifthen package.

Note that the content for \foreach is executed inside a group and assignments which should survive to the next iteration or after the end of the loop must be global. Luckily the above set and add macros are global assignments anyway.