Compilare: user.cpp: In function ‘void read()’: user.cpp:51: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result user.cpp:52: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result user.cpp:57: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result user.cpp: In function ‘void get_primes()’: user.cpp:175: warning: comparison between signed and unsigned integer expressions user.cpp:180: warning: comparison between signed and unsigned integer expressions user.cpp:185: warning: comparison between signed and unsigned integer expressions user.cpp: In function ‘void encode(int, number)’: user.cpp:205: warning: comparison between signed and unsigned integer expressions user.cpp:216: warning: comparison between signed and unsigned integer expressions user.cpp: In function ‘void print()’: user.cpp:235: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result