I have the following piece of latex code:

```
\def\a{1}
\def\b{2}
\def\c{\a+\b}
\def\d{\c/2}

```

I expected \d to have the value 1.5. But it did not. However, adding parenthesis to the definition of \c like

```
\def\c{\a+\b}

```

Doesn't work either, because if I use \c somewhere, it complains about the parenthesis. Is there a way to evaluate \c before dividing it by 2 in the definition of \d? Like:

```
\def\d{\eval{\c}/2}

```

(I made that \eval up to show what I mean)