Compilare: user.cpp: In function ‘void back(int)’: user.cpp:22: warning: statement is a reference, not call, to function ‘exit’ user.cpp:22: warning: statement has no effect user.cpp: In function ‘int main()’: user.cpp:106: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result user.cpp:107: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result user.cpp:108: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result user.cpp:110: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result