Tikz/Pgf if statements

Question

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:

\Atom{}{90/west/0,270/east/1}

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

\AtomSquash{}{90/west/sq,270/east/sq}

The code for creating the atoms is as follows

\newcommand{\Atom}[3][AtomNode]{
  \node[atomcore] (#1){#2};% {\ce{#2}};
  \foreach \ang/\anchor/\n in {#3} {
      \orbital{\ang}{#1.\anchor}{\n}
  }
}
\newcommand{\AtomSquash}[3][AtomNode]{
        \node[atomcore] (#1){#2};
        \foreach \ang/\anchor/\squashness in {#3}{
                \squashorbital{\ang}{#1.\anchor}{\squashness}
        }

}

And the orbital code:

\newcommand{\orbital}[3]{
    \begin{scope}[rotate=#1,shift=(#2)]
        % 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);
  \end{pgfonlayer}

  % Draw the electrons
  \ifnum#3>0
      \foreach \n in {1,...,#3} {
          %Don't need electrons to be shaded.
          %\shade[ball color=electron] (e\n) circle (1mm);
      }
  \fi
}

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.

Help?

Answer 1

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:

\ifthenelse{\equal{#3}{sq}}
           {... 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 ...}

Answer 2

With TeX primitives you can do something like

\def\sqstr{sq}
\def\argiii{#3}
\ifx\argiii\sqstr
  % #3==sq code
\else
  % #3!=sq code
\fi

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