I'm continuing my work on the "changeable" graphics. I have an array of values, and I have already succeeded in making variables from it. The next step is that I want to ignore the zero values. Here it is, what I have a problem with:

```
\pgfmathifthenelse{\myq==0}{}{\fill (B) circle (4pt)};
```

I thought this code should draw a circle in the node `B`

in case the variable `\myq`

has non-zero value. But I cannot even compile the code, compilation freezes. Can you figure out the possible problem or give an advice?

The whole code is:

```
\begin{tikzpicture}
\def\zamkl{{3,4,4.5,5}}
\def\zamkh{{4,3.5,5,4.5}}
\def\zamkq{{20,0,30,0}}
\pgfmathparse{\zamkl[0]}
\edef\myl{\pgfmathresult}
\pgfmathparse{\zamkh[0]}
\edef\myh{\pgfmathresult}
\pgfmathparse{\zamkq[0]}
\edef\myq{\pgfmathresult}
\draw[help lines] (0,0) grid (2*\myl,2*\myh);
\coordinate (A) at (0,0);
\coordinate (B) at (\myl,0); \node at (B) [below] {$T$};
\coordinate (C) at (2*\myl,0);
\coordinate (D) at (2*\myl,\myh); \node at (D) [left] {$S$};
\coordinate (E) at (2*\myl,2*\myh);
\coordinate (F) at (\myl,2*\myh); \node at (F) [below] {$R$};
\coordinate (G) at (0,2*\myh);
\coordinate (H) at (0,\myh); \node at (H) [right] {$W$};
\draw [very thick] (A) -- (C) -- (E) --(G) -- (A);
\pgfmathifthenelse{\myq==0}{}{\fill (B) circle (4pt)};
\end{tikzpicture}
```

## Best Answer

With pgfmath the correct syntax is

or

Every expression is expanded with

`\edef`

before it is parsed. Using`\noexpand`

protects`\fill`

from this expansion. And as always`\pgfmathifthenelse`

returns the result in the macro`\pgfmathresult`

.