Compilare: user.cpp: In function ‘void back()’: user.cpp:62: warning: unused variable ‘k’ user.cpp: In function ‘int main()’: user.cpp:84: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result user.cpp:85: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result user.cpp:87: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result user.cpp:92: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result