memory leak while trying to update/alter column in postgresql

I am trying to update/alter two columns-comment and id in a table called
xxx using postgresql. Though the compiler does not show any errors but
Valgrind gives major memory leak errors. The code is:

int main()
{
PGconn *conn;
PGresult *res;
int i=0,nFields=0,row=0,col=0;

conn = PQconnectdb("dbname=test1 host=localhost user=postgres
password=yyy");
if(PQstatus(conn) == CONNECTION_BAD)
{
fprintf(stderr, "Connection to database \"%s\" failed.\n",
PQerrorMessage(conn));
fprintf(stderr, "%s", PQerrorMessage(conn));
exit_nicely(conn);
}

res = PQexec(conn, "IF COL_LENGTH('xxx','comment') IS NULL");
if(res)
res = PQexec(conn, "ALTER TABLE xxx ADD comment VARCHAR(500)");
else
res = PQexec(conn, "UPDATE TABLE xxx ADD comment VARCHAR(500)");

res = PQexec(conn, "IF COL_LENGTH('xxx','id') IS NULL");
if(res)
res = PQexec(conn, "ALTER TABLE xxx ADD id VARCHAR(50)");
else
res = PQexec(conn, "UPDATE TABLE xxx ADD id VARCHAR(50)");

res = PQexec(conn, "SELECT * FROM xxx");
if((!res) || (PQresultStatus(res) != PGRES_TUPLES_OK))
{
fprintf(stderr, "SELECT command did not return tuples properly\n");
PQclear(res);
}

PQclear(res);
PQfinish(conn);

return 0;
}

Valgrind gives the following errors:

$ valgrind --track-origins=yes --leak-check=full ./Gwidd_uniprot_map2 xaa

==4525== Memcheck, a memory error detector
==4525== Copyright (C) 2002-2010, and GNU GPL'd, by Julian Seward et al.
==4525== Using Valgrind-3.6.1 and LibVEX; rerun with -h for copyright info
==4525== Command: ./Gwidd_uniprot_map2 xaa
==4525==
--4525-- ./Gwidd_uniprot_map2:
--4525-- dSYM directory has wrong UUID; consider using --dsymutil=yes
==4525==
==4525== HEAP SUMMARY:
==4525== in use at exit: 262,994 bytes in 751 blocks
==4525== total heap usage: 1,012 allocs, 261 frees, 345,158 bytes
allocated
==4525==
==4525== 2,248 (200 direct, 2,048 indirect) bytes in 1 blocks are
definitely lost in loss record 400 of 414
==4525== at 0x100011345: malloc (vg_replace_malloc.c:236)
==4525== by 0x10007B7E0: PQmakeEmptyPGresult (in /usr/lib/libpq.5.dylib)
==4525== by 0x10008DF30: pqGetErrorNotice3 (in /usr/lib/libpq.5.dylib)
==4525== by 0x10008CC00: pqParseInput3 (in /usr/lib/libpq.5.dylib)
==4525== by 0x10007ECD9: parseInput (in /usr/lib/libpq.5.dylib)
==4525== by 0x10007EE3F: PQgetResult (in /usr/lib/libpq.5.dylib)
==4525== by 0x10007F6F1: PQexecFinish (in /usr/lib/libpq.5.dylib)
==4525== by 0x10007F1DC: PQexec (in /usr/lib/libpq.5.dylib)
==4525== by 0x10000199A: main (in ./Gwidd_uniprot_map2)
==4525==
==4525== 2,248 (200 direct, 2,048 indirect) bytes in 1 blocks are
definitely lost in loss record 401 of 414
==4525== at 0x100011345: malloc (vg_replace_malloc.c:236)
==4525== by 0x10007B7E0: PQmakeEmptyPGresult (in /usr/lib/libpq.5.dylib)
==4525== by 0x10008DF30: pqGetErrorNotice3 (in /usr/lib/libpq.5.dylib)
==4525== by 0x10008CC00: pqParseInput3 (in /usr/lib/libpq.5.dylib)
==4525== by 0x10007ECD9: parseInput (in /usr/lib/libpq.5.dylib)
==4525== by 0x10007EE3F: PQgetResult (in /usr/lib/libpq.5.dylib)
==4525== by 0x10007F6F1: PQexecFinish (in /usr/lib/libpq.5.dylib)
==4525== by 0x10007F1DC: PQexec (in /usr/lib/libpq.5.dylib)
==4525== by 0x1000019B5: main (in ./Gwidd_uniprot_map2)
==4525==
==4525== 2,248 (200 direct, 2,048 indirect) bytes in 1 blocks are
definitely lost in loss record 402 of 414
==4525== at 0x100011345: malloc (vg_replace_malloc.c:236)
==4525== by 0x10007B7E0: PQmakeEmptyPGresult (in /usr/lib/libpq.5.dylib)
==4525== by 0x10008DF30: pqGetErrorNotice3 (in /usr/lib/libpq.5.dylib)
==4525== by 0x10008CC00: pqParseInput3 (in /usr/lib/libpq.5.dylib)
==4525== by 0x10007ECD9: parseInput (in /usr/lib/libpq.5.dylib)
==4525== by 0x10007EE3F: PQgetResult (in /usr/lib/libpq.5.dylib)
==4525== by 0x10007F6F1: PQexecFinish (in /usr/lib/libpq.5.dylib)
==4525== by 0x10007F1DC: PQexec (in /usr/lib/libpq.5.dylib)
==4525== by 0x1000019DF: main (in ./Gwidd_uniprot_map2)
==4525==
==4525== 2,248 (200 direct, 2,048 indirect) bytes in 1 blocks are
definitely lost in loss record 403 of 414
==4525== at 0x100011345: malloc (vg_replace_malloc.c:236)
==4525== by 0x10007B7E0: PQmakeEmptyPGresult (in /usr/lib/libpq.5.dylib)
==4525== by 0x10008DF30: pqGetErrorNotice3 (in /usr/lib/libpq.5.dylib)
==4525== by 0x10008CC00: pqParseInput3 (in /usr/lib/libpq.5.dylib)
==4525== by 0x10007ECD9: parseInput (in /usr/lib/libpq.5.dylib)
==4525== by 0x10007EE3F: PQgetResult (in /usr/lib/libpq.5.dylib)
==4525== by 0x10007F6F1: PQexecFinish (in /usr/lib/libpq.5.dylib)
==4525== by 0x10007F1DC: PQexec (in /usr/lib/libpq.5.dylib)
==4525== by 0x1000019FA: main (in ./Gwidd_uniprot_map2)
==4525==
==4525== LEAK SUMMARY:
==4525== definitely lost: 800 bytes in 4 blocks
==4525== indirectly lost: 8,192 bytes in 4 blocks
==4525== possibly lost: 0 bytes in 0 blocks
==4525== still reachable: 254,002 bytes in 743 blocks
==4525== suppressed: 0 bytes in 0 blocks
==4525== Reachable blocks (those to which a pointer was found) are not
shown.
==4525== To see them, rerun with: --leak-check=full --show-reachable=yes
==4525==
==4525== For counts of detected and suppressed errors, rerun with: -v
==4525== ERROR SUMMARY: 4 errors from 4 contexts (suppressed: 0 from 0)
Please provide suggestions to solve the problem.

Thanks!