Cdtrjyty

The white/black board can be drawn by testing the parity of node positions as follows:

documentclass[tikz]{standalone}

usepackage{xifthen}



begin{document}

begin{tikzpicture}[every node/.style = {draw, circle, minimum size = 10pt}]

  foreach r in {1, ..., 4} {

    foreach c in {1, ..., 5} {

      pgfmathparse{mod(r + c, 2)} 

      letparitypgfmathresult 



      ifthenelse{equal{parity}{0.0}}

      {node (rc) [fill = lightgray] at (c, r){}}

      {node (rc) at (c, r){}};

    }

  }

end{tikzpicture}

end{document}

However, using isodd of xifthen does not produce the same result. What is wrong here? Or are there any alternative similar solutions?

documentclass[tikz]{standalone}

usepackage{xifthen}



begin{document}

begin{tikzpicture}[every node/.style = {draw, circle, minimum size = 10pt}]

  foreach r in {1, ..., 4} {

    foreach c in {1, ..., 5} {

      ifthenelse{NOT isodd{r + c}}

      {node (rc) [fill = lightgray] at (c, r){}}

      {node (rc) at (c, r){}};

    }

  }

end{tikzpicture}

end{document}

I'd suggest using TeX's ifodd (or etoolbox); xifthen-and-friends may be considered obsolete:

documentclass{article}



usepackage{xfp,tikz}



begin{document}



begin{tikzpicture}[every node/.style = {draw, circle, minimum size = 10pt}]

  foreach r in {1, ..., 4} {

    foreach c in {1, ..., 5} {

      ifoddinteval{r+c}

        node (rc) [fill = lightgray] at (c, r) {};

      else

        node (rc) at (c, r) {};

      fi

    }

  }

end{tikzpicture}



end{document}

I use xfp since it is convenient and provides an expandable inteval for integer evaluation that can be used in conditioning options like ifodd. You can also do it without xfp:

      ifoddnumexprr+crelax

      %...

You are implicitly assuming that isodd does calculations. But this is not what happens, it actually simply takes the begin of the argument until it hits something that is no longer a number. So you would need to do the addition first and then fed the result to isodd. Or use the tools of pgf:

documentclass{article}

usepackage{tikz}

usepackage{xifthen}



begin{document}

ifthenelse{isodd{124blub}}{odd}{even}



ifthenelse{isodd{123blub}}{odd}{even}



ifthenelse{isodd{2+3}}{odd}{even}



ifthenelse{isodd{3+2}}{odd}{even}



bigskip

begin{tikzpicture}[every node/.style = {draw, circle, minimum size = 10pt}]

  foreach r in {1, ..., 4} {

    foreach c in {1, ..., 5} {

      pgfmathsetmacromycolor{isodd{numexprr+c}?"lightgray":"white"}

      node (rc) [fill =mycolor  ] at (c, r){};

    }

  }

end{tikzpicture}

end{document}