
Now look at the Tcl interface:
</p>

<div class="code"><pre>
% puts $density          # Output value of C global variable
1.0
% set density 0.95       # Change value
</pre></div>

<p>
If you make an error in variable assignment, you will get an
error message.  For example:
</p>

<div class="code"><pre>
% set density "hello"
can't set "density": Type error. expected a double.
%
</pre></div>

<p>
If a variable is declared as <tt>const</tt>, it is wrapped as a
read-only variable.  Attempts to modify its value