Is this a right statement?

From: Sam Kong (sam.s.kong_at_gmail.com)
Date: 02/11/05 

Date: 10 Feb 2005 15:34:32 -0800

Hello!

I read an article and read the following sentence.
(From http://acmqueue.com/modules.php?name=Content&pa=showpage&pid=273)
I am not sure what that means.

<snip>
Then there was Simula, which the designers thought of as an extension
of Algol. It was basically a preprocessor to Algol the way C++ was a
preprocessor for C.
</snip>

Is C++ a preprocessor for C?
What does that mean?
Is it right?

TIA.
Sam