How to use mod operation in latex with tikz

Question

I need something similar to

\ifnum \j mod 2 = 0

rest of a number, but do not know how to do this

in line 22.

\documentclass{article}
\usepackage{tikz}
\usepackage[active,tightpage]{preview}
\PreviewEnvironment{tikzpicture}
\setlength\PreviewBorder{0pt}%

\newcommand{\grade}{
    \foreach \k in {0,...,9}{
        \draw[dashed] (\k,0) -- ++(0,10);
        \draw[dashed] (0,\k) -- ++(10,0);
    }
}

\begin{document}
\foreach \j in {1,...,9}{
    \foreach \i in {1,...,9}{
        \begin{tikzpicture}[y=-1cm]
            \clip[fill=white] (1,1) rectangle (10,10);
            \grade
            %animation
            \ifnum \j < 5
                \fill[blue] (\i,\j) rectangle ++(1,1);
            \else
                \fill[blue] (\j,\i) rectangle ++(1,1);
            \fi
        \end{tikzpicture}
    }
}
\end{document}

There is the primitive conditional \ifodd – egreg Jun 22 '12 at 12:08 — egreg, Jun 22 '12 at 12:08
\ifnum \j mod 3 = 0 or other number? how to calculate? – Regis Santos Jun 22 '12 at 12:18 — Regis Santos, Jun 22 '12 at 12:18

score 14 · Accepted Answer · answered Jun 22 '12 at 12:21

As egreg mentions there are already primitives available. Also the CVS version of TikZ/PGF 2.1 will bring iseven,isodd,isprime functions. However you can also use a slightly redundant ifthenelse function as follows:

\documentclass{article}
\usepackage{tikz}

\newcommand{\grade}{
    \foreach \k in {0,...,9}{
        \draw[dashed] (\k,0) -- ++(0,10) (0,\k) -- ++(10,0);
    }
}
\begin{document}

\begin{tikzpicture}[y=-1cm]\grade
\foreach \j in {1,...,9}{
    \foreach \i in {1,...,9}{
    \pgfmathparse{Mod(\j,2)==0?1:0}
    \ifnum\pgfmathresult>0
                \fill[blue] (\i,\j) rectangle ++(1,1);
    \else
                \fill[blue] (\j,\i) rectangle ++(1,1);
    \fi
    }
}
\end{tikzpicture}
\end{document}

enter image description here

I hope I've understood the goal correctly.

How to use mod operation in latex with tikz

1 Answers1

Linked