Compilare: main.cpp: In function 'int main()': main.cpp:111:12: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] while (i < event.size()) { ~~^~~~~~~~~~~~~~ main.cpp:113:14: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] while (j < event.size() && event[i].a == event[j].a) { ~~^~~~~~~~~~~~~~ main.cpp:120:11: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if (j != event.size()) ~~^~~~~~~~~~~~~~~