Graphics, Figures & Tables ⇒ tikZ | '\foreach' Problem

[jhapk]

Hi,

can anyone please explain why is the following code not working?

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\documentclass{minimal}
\usepackage{tikz}
\begin{document}
\begin{tikzpicture}

  \def\width{2.5}
  \def\unit{0.5*\width}
  
  \foreach \p in {0,\unit,...,\width}
  \draw (\p,0) -- (\p,1);

\end{tikzpicture}
\end{document}

I get the following error message:

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! Illegal unit of measure (pt inserted).
<to be read again> 
                   *
l.13   \draw (\p,0) -- (\p,1);
                              
? x

[frederic]

I find \foreach a little buggy when not looping over integers. For this reason I suggest the following code. I also modified the relationship between

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\width

and

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\unit

.

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\begin{tikzpicture}

  \def\width{2.5}
  \def\unit{0.3}
  \pgfmathtruncatemacro{\kmax}{div(\width,\unit)}
  
  \foreach \k [evaluate=\k as \x using \k*\unit] in {0,...,\kmax}{
    \draw (\x,0) -- (\x,1);
  }
 
\end{tikzpicture}

[shadgrind]

I tried this to see why you're getting that error:

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\documentclass{minimal}
\usepackage{tikz}
\begin{document}
\begin{tikzpicture}
    \def\width{2.5}
    \def\unit{0.5*\width}
    \foreach \p in {0,\unit,\width}
       \draw (\p,0) -- (\p,1) node[above] {\p};
\end{tikzpicture}
\end{document}

It compiles, and the second line will have the node "0.5*2.5" above it. So maybe TikZ is getting confused about whether to treat the value of \unit as the numeric value 1.25 or as the string "0.5*2.5". Because if you replace \unit with its numeric value 1.25 in the \foreach command in your original example, it works. So I would say ditch \unit.