Compilare: user.cpp: In function ‘int main()’: user.cpp:50:45: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (; a < str[i].sir.size () && b < str[j].sir.size (); ++a) ^ user.cpp:50:71: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (; a < str[i].sir.size () && b < str[j].sir.size (); ++a) ^ user.cpp:53:43: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if (b == str[j].sir.size ()) ^