Compilare: main.cpp: In function 'int main()': main.cpp:29:34: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result [-Wunused-result] freopen("farey.in","r",stdin); ^ main.cpp:30:36: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result [-Wunused-result] freopen("farey.out","w",stdout); ^ main.cpp:31:25: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result] scanf("%d %d",&n,&k); ^ main.cpp:48:28: warning: 'ans' may be used uninitialized in this function [-Wmaybe-uninitialized] double j=(double)i*ans; ^~~