libpq Newbie question

Hi, I'm a newbie in postgresql, would like to know how to access database
using libpq. I found example code on postgresql's site, however i'm not able
to execute the code it always giving me an error.
I hope anyone could explain to me how to fix this.
Thank you.

Error:
Undefined first referenced
symbol in file
PQresultStatus /var/tmp/ccED8fcw.o
PQclear /var/tmp/ccED8fcw.o
PQexec /var/tmp/ccED8fcw.o
PQerrorMessage /var/tmp/ccED8fcw.o
PQstatus /var/tmp/ccED8fcw.o
PQconsumeInput /var/tmp/ccED8fcw.o
PQnotifies /var/tmp/ccED8fcw.o
PQfinish /var/tmp/ccED8fcw.o
PQsetdbLogin /var/tmp/ccED8fcw.o
ld: fatal: Symbol referencing errors. No output written to a.out
collect2: ld returned 1 exit status

The code:
/*
* testlibpq2.c
* Test of the asynchronous notification interface
*
* Start this program, then from psql in another window do
* NOTIFY TBL2;
*
* Or, if you want to get fancy, try this:
* Populate a database with the following:
*
* CREATE TABLE TBL1 (i int4);
*
* CREATE TABLE TBL2 (i int4);
*
* CREATE RULE r1 AS ON INSERT TO TBL1 DO
* (INSERT INTO TBL2 values (new.i); NOTIFY TBL2);
*
* and do
*
* INSERT INTO TBL1 values (10);
*
*/
#include <stdio.h>
#include "libpq-fe.h"
void
exit_nicely(PGconn *conn)
{
PQfinish(conn);
exit(1);
}
main()
{
char *pghost,
*pgport,
*pgoptions,
*pgtty;
char *dbName;
int nFields;
int i,
j;
PGconn *conn;
PGresult *res;
PGnotify *notify;
/*
* begin, by setting the parameters for a backend connection if the
* parameters are null, then the system will try to use reasonable
* defaults by looking up environment variables or, failing that,
* using hardwired constants
*/
pghost = NULL; /* host name of the backend server */
pgport = NULL; /* port of the backend server */
pgoptions = NULL; /* special options to start up the backend
* server */
pgtty = NULL; /* debugging tty for the backend server */
dbName = getenv("USER"); /* change this to the name of your test
* database */
/* make a connection to the database */
conn = PQsetdb(pghost, pgport, pgoptions, pgtty, dbName);
/*
* check to see that the backend connection was successfully made
*/
if (PQstatus(conn) == CONNECTION_BAD)
{
fprintf(stderr, "Connection to database '%s' failed.\n", dbName);
fprintf(stderr, "%s", PQerrorMessage(conn));
exit_nicely(conn);
}
res = PQexec(conn, "LISTEN TBL2");
if (!res || PQresultStatus(res) != PGRES_COMMAND_OK)
{
fprintf(stderr, "LISTEN command failed\n");
PQclear(res);
exit_nicely(conn);
}
/*
* should PQclear PGresult whenever it is no longer needed to avoid
* memory leaks
*/
PQclear(res);
while (1)
{
/*
* wait a little bit between checks; waiting with select()
* would be more efficient.
*/
sleep(1);
/* collect any asynchronous backend messages */
PQconsumeInput(conn);
/* check for asynchronous notify messages */
while ((notify = PQnotifies(conn)) != NULL)
{
fprintf(stderr,
"ASYNC NOTIFY of '%s' from backend pid '%d' received\n",
notify->relname, notify->be_pid);
free(notify);
}
}
/* close the connection to the database and cleanup */
PQfinish(conn);
return 0;
}