compile error - Mailing list pgsql-interfaces

hello ,

can somebody explain to me why when I compile the following program i do
not know
how to link the libraries to c .

---------------------

#include <stdio.h>
#include "libpq-fe.h"

void exit_nicely(PGconn* conn)
{
 PQfinish(conn);
 exit(1);
}

main()
{
 printf("\nThe End\n") ;
}

-----------------------
I get the following error

        tmp/cca006421.o: In function `exit nicely'
        tmp/cca006421.o(.text+0x8): undefined reference to `PQfinish'


Thanks ,
Rony .