Compilare: user.cpp: In function ‘int main()’: user.cpp:126:38: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] } else if(used.size() == itr + 1 && used[itr] == cap[itr]) { ^ In file included from /usr/include/c++/4.8/cassert:43:0, from user.cpp:4: user.cpp:140:30: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] assert(used.size() > itr); ^