Compilare: user.cpp: In function ‘int main()’: user.cpp:38:38: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i = 0; i < str.size(); ++ i) ^ user.cpp:63:34: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (i = 0; i < str.size(); ++ i) ^ user.cpp:86:27: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] if (i == str.size()) ^