Compilare: user.cpp: In function ‘void read()’: user.cpp:52: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result user.cpp:53: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result user.cpp:58: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result user.cpp: In function ‘void get_primes()’: user.cpp:176: warning: comparison between signed and unsigned integer expressions user.cpp:181: warning: comparison between signed and unsigned integer expressions user.cpp:186: warning: comparison between signed and unsigned integer expressions user.cpp: In function ‘void encode(int, number)’: user.cpp:206: warning: comparison between signed and unsigned integer expressions user.cpp:218: warning: comparison between signed and unsigned integer expressions user.cpp: In function ‘void print()’: user.cpp:238: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result