Compilare: user.cpp: In function ‘void read()’: user.cpp:23: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result user.cpp:26: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result user.cpp: In function ‘void back(int)’: user.cpp:41: warning: comparison between signed and unsigned integer expressions