passing variable between cgi

Hello,
I am setting up PostgreSQL (postgresql-6.4.2) database in Linux (Linux 2.0.27)
system, and want to access the database with cgi ( C program) through Apache
(version 1.1) server.  My application involve a few cgi programmes.
I can not figure out how to pass varibles between cgi programmes.

My application involve some thing like this:
    In a HTML page, when the user click a button, a cgi program will run and get
some data from Postgres, then when the user click another button, the other cgi
will be triggerred to process certain data got by the previous cgi, so, I will
need to pass the data get by the first cgi to the second cgi according to the
user choice ...

I am using the embedded SQL (ecpg) method to write the cgi ( C program ) to get
data from postgresql-6.4.2.
How should I pass variable between these C program?  What are the common methods
to develop this kind of application?
Please advice.
Thank you.
LCH