Compilare: user.cpp: In function ‘void write()’: user.cpp:45:34: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i = 1; i < len.size(); ++i) { ^ user.cpp: In function ‘int main()’: user.cpp:53:33: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("in.in", "r", stdin); ^ user.cpp:54:36: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("out.out", "w", stdout); ^