Compilare: user.cpp: In function ‘void back(int)’: user.cpp:9: warning: comparison between signed and unsigned integer expressions user.cpp:11: warning: comparison between signed and unsigned integer expressions user.cpp:19: warning: comparison between signed and unsigned integer expressions user.cpp: In function ‘int main()’: user.cpp:29: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result user.cpp:30: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result user.cpp:32: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result