Compilare: user.cpp: In function ‘int main()’: user.cpp:51: warning: operation on ‘co’ may be undefined user.cpp:82: warning: operation on ‘co’ may be undefined user.cpp:112: warning: operation on ‘co’ may be undefined user.cpp:143: warning: operation on ‘co’ may be undefined user.cpp:13: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result user.cpp:14: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result user.cpp:15: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result user.cpp:20: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result