Compilare: user.cpp: In function ‘std::vector<int> pre(std::string)’: user.cpp:16:32: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i = 2; i <= s.size(); ++i) ^ user.cpp: In function ‘int main()’: user.cpp:49:36: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int j = 0; j <= s.size(); ++j) ^ user.cpp:54:35: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int j = 0; j < s.size(); ++j) ^ user.cpp:103:31: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i = 0; i < s.size(); ++i) ^