Compilare: user.cpp: In function ‘void insert_str(std::string)’: user.cpp:22:32: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i = 0; i < s.size(); i++) ^ user.cpp: In function ‘void delete_str(std::string)’: user.cpp:38:32: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i = 0; i < s.size(); i++) ^ user.cpp: In function ‘int count_str(std::string)’: user.cpp:51:32: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i = 0; i < s.size(); i++) ^ user.cpp: In function ‘int lcs_str(std::string)’: user.cpp:67:32: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i = 0; i < s.size(); i++) ^