Compilare: user.cpp: In function ‘int main()’: user.cpp:73:29: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int aIdx = 1; aIdx <= a.size(); ++aIdx) { ~~~~~^~~~~~~~~~~ user.cpp:76:33: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int bIdx = 1; bIdx <= b.size(); ++bIdx) { ~~~~~^~~~~~~~~~~