Compilare: main.cpp: In function 'int is_prime(long long int)': main.cpp:34:25: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for ( int d = 0 ; d < primes.size () && primes [ d ] * primes [ d ] <= n ; ++ d ) ~~^~~~~~~~~~~~~~~~ main.cpp: In function 'int main()': main.cpp:45:43: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result [-Wunused-result] freopen ( "superp.in" , "r" , stdin ) ; ^ main.cpp:46:45: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result [-Wunused-result] freopen ( "superp.out" , "w" , stdout ) ; ^ main.cpp:51:26: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result] scanf ( "%d" , & n ) ; ^ main.cpp:56:32: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result] scanf ( "%lld" , & x ) ; ^