Compilare: user.cpp: In function ‘int main()’: user.cpp:68:34: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int j = 0; j < up[i].size(); ++j) { ^ user.cpp:72:39: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int j = 0; j < event[val].size(); ++j) { ^ user.cpp:83:29: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i = 0; i < v.size(); ++i) { ^