C++ code - PGRES_TUPLES_OK is not returned when DELETE performed

I realize for the following code :

PGconn *connection = this->connection.getConnection();
PGresult *res = PQexec(connection, "DELETE FROM measurement_statistic WHERE fk_lot_id = 47");

// status always false??
const bool status = (PQresultStatus(res) == PGRES_TUPLES_OK);

status will always remain false, although the actual row in database had been delete.

I execute the above statement (DELETE FROM measurement_statistic WHERE fk_lot_id = 47) through pgadmin. It works fine.

May I know why PGRES_TUPLES_OK is not being returned when I use DELETE? When I try to execute SELECT statement,
PGRES_TUPLES_OKcan be returned. 

Thanks and Regards
Yan Cheng CHEOK