Compilare: user.cpp: In function ‘void write_data()’: user.cpp:20: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result user.cpp: In function ‘int main()’: user.cpp:48: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result user.cpp:49: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result