Compilare: user.cpp: In function ‘int main()’: user.cpp:8:40: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen( "nrtri.in" , "r" , stdin ); ^ user.cpp:9:40: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen( "nrtri.out", "w" , stdout); ^ user.cpp:10:23: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] scanf("%d\n" , &n); ^ user.cpp:11:43: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] for(i=1;i<=n;++i){ scanf("%d ", &v[i]); us[v[i]]++; } ^ user.cpp:12:51: warning: iteration 849u invokes undefined behavior [-Waggressive-loop-optimizations] for(i=1;i<=30000;++i) sum[i] = sum[i-1] + us[i]; ^ user.cpp:12:5: note: containing loop for(i=1;i<=30000;++i) sum[i] = sum[i-1] + us[i]; ^