Gfrktyl

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}

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}

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

      %...

isodd doesn't compute; you might do

expandafterifthenelseexpandafter{expandafterNOTexpandafterisoddexpandafter{thenumexprr+c}}

but it's not something I'd use myself. ;-)

Here's a (partial) reimplementation of xifthen allowing expressions; the syntax is different, though: for parentheses you use ( and ) rather than ( and ). For the connectives, AND, OR and NOT are replaced respectively by &&, || and !.

documentclass{article}

usepackage{xparse}

usepackage{tikz} % for the application



ExplSyntaxOn

NewExpandableDocumentCommand{xifthenelse}{mmm}

 {

  bool_if:nTF { #1 } { #2 } { #3 }

 }



cs_new_eq:NN numtest int_compare_p:n

cs_new_eq:NN oddtest int_if_odd_p:n

cs_new_eq:NN dimtest dim_compare_p:n

cs_new_eq:NN deftest cs_if_exist_p:N

cs_new_eq:NN namedeftest cs_if_exist_p:c

cs_new_eq:NN eqdeftest token_if_eq_meaning_p:NN

cs_new_eq:NN streqtest str_if_eq_p:ee

cs_new_eq:NN emptytest tl_if_blank_p:n

prg_new_conditional:Nnn xxifthen_legacy_conditional:n { p,T,F,TF }

 {

  use:c { if#1 } prg_return_true: else: prg_return_false: fi:

 }

cs_new_eq:NN boolean xxifthen_legacy_conditional_p:n

ExplSyntaxOff



begin{document}



xifthenelse{emptytest{}}{true}{false} true



xifthenelse{emptytest{ }}{true}{false} true



xifthenelse{emptytest{ foo }}{true}{false} false



xifthenelse{numtest{10 * 10 + 1 > 100}}{true}{false} true



xifthenelse{numtest{10 * 10 + 1 > 100 * 100}}{true}{false} false



xifthenelse{eqdeftest{usepackage}{RequirePackage}}{true}{false} true



xifthenelse{eqdeftest{usepackage}{textit}}{true}{false} false



xifthenelse{namedeftest{@foo}}{true}{false} false



xifthenelse{namedeftest{@for}}{true}{false} true



xifthenelse{namedeftest{@for} || numtest{1>2}}{true}{false} true



xifthenelse{namedeftest{@for} && numtest{1>2}}{true}{false} false



xifthenelse{namedeftest{@for} && !numtest{1>2}}{true}{false} true



xifthenelse{!oddtest{1+3}}{true}{false} true



xifthenelse{boolean{mmode}}{true}{false} false



$xifthenelse{boolean{mmode}}{true}{false}$ true



bigskip



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

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

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

      xifthenelse{!oddtest{r+c}}

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

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

    }

  }

end{tikzpicture}



end{document}

Of course, using PGF methods for the picture case is much easier.