Compilare: user.cpp: In function ‘int main()’: user.cpp:18:9: warning: unused variable ‘a’ [-Wunused-variable] int n, a, b; ^ user.cpp:18:12: warning: unused variable ‘b’ [-Wunused-variable] int n, a, b; ^ user.cpp:15:34: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("twoton.in", "r", stdin); ^ user.cpp:16:36: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("twoton.out", "w", stdout); ^ user.cpp:23:17: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] scanf("%d", &n); ^ user.cpp:28:21: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] scanf("%d", &v[i]); ^