perspic.cpp: In function 'void read_eval()': perspic.cpp:28: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result perspic.cpp:32: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result perspic.cpp:45: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result perspic.cpp: In function 'void gen_primes()': perspic.cpp:85: warning: unused variable 'i' perspic.cpp: In function 'int main()': perspic.cpp:127: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result perspic.cpp:128: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result