Compilare: user.cpp: In function ‘void add_(std::string)’: user.cpp:28: warning: comparison between signed and unsigned integer expressions user.cpp:34: warning: comparison between signed and unsigned integer expressions user.cpp: In function ‘void del_(std::string)’: user.cpp:46: warning: comparison between signed and unsigned integer expressions user.cpp:49: warning: comparison between signed and unsigned integer expressions user.cpp: In function ‘void print_nrCuv(std::string)’: user.cpp:61: warning: comparison between signed and unsigned integer expressions user.cpp: In function ‘void print_pref(std::string)’: user.cpp:74: warning: comparison between signed and unsigned integer expressions user.cpp: In function ‘int main()’: user.cpp:138: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result