Compilare: In file included from /usr/include/c++/4.4/ext/hash_set:60, from user.cpp:3: /usr/include/c++/4.4/backward/backward_warning.h:28:2: warning: #warning This file includes at least one deprecated or antiquated header which may be removed without further notice at a future date. Please use a non-deprecated interface with equivalent functionality instead. For a listing of replacement headers and interfaces, consult the file backward_warning.h. To disable this warning use -Wno-deprecated. user.cpp: In function ‘int main()’: user.cpp:16: warning: unused variable ‘mel’