Compilare: user.cpp: In function ‘HN& sum(HN&, HN&)’: user.cpp:38:8: warning: reference to local variable ‘ans’ returned [-Wreturn-local-addr] HN ans; ^ user.cpp: In function ‘HN& dif(HN&, HN&)’: user.cpp:53:8: warning: reference to local variable ‘ans’ returned [-Wreturn-local-addr] HN ans; ^ user.cpp: In function ‘HN& prod(HN&, HN&)’: user.cpp:70:8: warning: reference to local variable ‘ans’ returned [-Wreturn-local-addr] HN ans; ^ user.cpp: In function ‘int main()’: user.cpp:106:36: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("indep.in", "r", stdin); ^ user.cpp:107:38: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("indep.out", "w", stdout); ^ user.cpp:109:20: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] scanf("%d", &n); ^ user.cpp:113:27: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] scanf("%d", &a[i]); ^