Compilare: user.cpp: In function ‘int main()’: user.cpp:21:30: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i = 0; i < s1.size(); i++) ^ user.cpp:25:30: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i = 0; i < s1.size(); i++) ^ user.cpp:31:38: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i = s1.size(); i < s2.size(); i++) ^