Compilare: main.cpp: In function 'int main()': main.cpp:62:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i = 0; i < a.size(); i++) ~~^~~~~~~~~~ main.cpp:67:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i = 0; i < a.size(); i++) ~~^~~~~~~~~~ main.cpp:69:19: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i=0; i<a.size(); ++i) ~^~~~~~~~~