libpq can't do "insert"

I have a question on the libpq( c language) libraries.
The included testlibpq.c can extract data from the postgres95 database.
Modifing the testlibpq.c enable me to extract data from any database in the
postgres95. Hovever, when I changed the "select" query to "insert" query, the
code seems doesn't work. Could somebody tell me is it another way to do
"insert" or something I have missed?

eg.
res=PQexec(conn, "DECLARE myportal CURSOR FOR select * .......");
was changed to
res=PQexec(conn, "DECLARE myportal CURSOR FOR insert into .......");
But can't do insert.

--
Regards, Christopher Luk
   System Analyst - The Hong Kong Council of the Church of Christ in China
              Phone : (852) 2397-1022 Fax : (852) 2397-7405
     mailto:wluk@hkcccc.org URL : http://www.hkcccc.org (Chinese based)