Compilare: user.cpp: In function ‘void adauga(std::string)’: user.cpp:24:28: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i =0; i<s.size(); i++) ^ user.cpp: In function ‘void sterge(std::string)’: user.cpp:40:28: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i =0; i<s.size(); i++) ^ user.cpp: In function ‘int nr_aparitii(std::string)’: user.cpp:57:28: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i =0; i<s.size(); i++) ^ user.cpp: In function ‘int prefix(std::string)’: user.cpp:67:28: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i =0; i<s.size(); i++) ^ user.cpp:76:1: warning: control reaches end of non-void function [-Wreturn-type] } ^