Compilare: main.cpp: In function 'int main(int, const char**)': main.cpp:27:34: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result [-Wunused-result] freopen("pairs.in","r",stdin); ^ main.cpp:28:36: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result [-Wunused-result] freopen("pairs.out","w",stdout); ^ main.cpp:32:19: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result] scanf("%d",&n); ^ main.cpp:36:23: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result] scanf("%d",&x); ^ main.cpp: In function 'void ciur()': main.cpp:17:24: warning: iteration 1000003 invokes undefined behavior [-Waggressive-loop-optimizations] if(!cateprime[i]) ~~~~~~~~~~~^ main.cpp:16:18: note: within this loop for(int i=2;i<=nmax;i++) ~^~~~~~