simple arithmetic on index of foreach statement in tikz

Question

Is foreach really a tikz statement or is derived from some other package?

I would like to draw a horizontal axis with 7 ticks spaced 1 cm apart. I'd like to place a label under each tick that is the ordinal number of the tick (1,2,3..) and a label above the tick that is the value of the ordinal number multiplied by the constant 3.14

Answer 1

Yes, foreach is a TikZ/PGF statement. It is described in the very detailed pgfmanual. You can also use it independently of TikZ/PGF by issuing \usepackage{pgffor} in your preamble. This is not necessary if you're using TikZ, as it will be loaded automatically.

Here's an example of how to achieve what you described in your question. \pgfmathsetmacro<macroname>{<expression>} uses the PGF math engine to do the calculation and assigns the result to a macro, while \pgfmathprintnumber rounds and outputs the result.

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

\begin{tikzpicture}

\foreach \x in {1,...,7} {
    \pgfmathsetmacro\result{\x * pi}
    \draw (\x,-4pt) -- (\x,4pt)
        node [below,yshift=-2ex] {\x}
        node [above] {\pgfmathprintnumber{\result}};
}

\draw [-latex] (1,0) -- (7.6,0);

\end{tikzpicture}
\end{document}