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I'm having trouble writing if statements, I can find next to no documentation on them and what I want to do seems quite simple.

I'm using the orbitals pgf/tikz example from here, and I'd like to write a new atom type, whereby instead of the third argument, it takes phrase describing squashedness

Normally, the code to create an atom looks like this:


So I wrote a separate method which I'm trying to modify that


The code for creating the atoms is as follows

  \node[atomcore] (#1){#2};% {\ce{#2}};
  \foreach \ang/\anchor/\n in {#3} {
        \node[atomcore] (#1){#2};
        \foreach \ang/\anchor/\squashness in {#3}{


And the orbital code:

        % These points define the curve for the orbital.
        \coordinate (c1) at (-\orbwidth, .6 * \orbheight);
        \coordinate (c2) at (-\orbwidth, \orbheight);
        \coordinate (c3) at (\orbwidth, \orbheight);
        \coordinate (c4) at (\orbwidth, .6 * \orbheight);
        \coordinate (top) at (0,\orbheight);

        %Coordinates of the electrons

        \coordinate (e1) at (0, 0.45*\orbheight);
        \coordinate (e2) at (0, 0.75*\orbheight);
    \end{scope}  \begin{pgfonlayer}{background}

      \draw[orbital #3] (#2) .. controls (c1) and (c2) .. (top) ..
            controls (c3) and (c4) .. (#2);

  % Draw the electrons
      \foreach \n in {1,...,#3} {
          %Don't need electrons to be shaded.
          %\shade[ball color=electron] (e\n) circle (1mm);

What I would especially like to do here, is have the \atom and \atomsquash in a single method, which would decide based on the number of arguments or say the text value of the third argument (is it equal to "sq" or is it a number?). I've tried writing an if statement that looks like the following \iftype=sq but the compiler seriously dislikes this. It doesn't help if I put quotes around the sq, the code will compile then but the if statement never is true.


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I don't quite understand what you mean by \iftype; this is not a defined control sequence as far as I know. Which code did compile? –  Hendrik Vogt Oct 28 '10 at 8:47
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2 Answers

up vote 11 down vote accepted

You can't compare strings easily using plain TeX's \ifs. If you're using LaTeX, I would use the ifthen package instead, which you almost definitely have installed already. With it, your desired if statement looks like this:

           {... code if #3 == sq ...}
           {... code if #3 != sq ...}

You can also do numeric tests within the condition, so for instance

\ifthenelse{\equal{#3}{sq} \OR #3 > 0}
           {... valid ...}
           {... invalid ...}
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With TeX primitives you can do something like

  % #3==sq code
  % #3!=sq code

I started out preferring ifthen.sty but for some reason nowadays I like TeX \ifs.

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Although this may not be a problem, note that this will fail if #3 is itself a macro (e.g., \maybeSQ). You could use \edef\argiii{#3}, but that fails if there's anything unexpandable in #3. I also started out preferring ifthen, and then moved to TeX \if structures; (I think it's because the syntax is nicer, even if it does have some strange properties); however, string equality is one place where I always use \ifthenelse, for reasons like this. –  Antal S-Z Oct 27 '10 at 20:05
@Antal: I think I do the exact same thing. –  Matthew Leingang Oct 27 '10 at 23:42
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