Compilare: user.cpp: In function ‘void prep()’: user.cpp:23: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result user.cpp:24: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result user.cpp:29: warning: ignoring return value of ‘size_t fread(void*, size_t, size_t, FILE*)’, declared with attribute warn_unused_result user.cpp: In function ‘int main()’: user.cpp:67: warning: left-hand operand of comma has no effect user.cpp:67: warning: left-hand operand of comma is a reference, not call, to function ‘gcd’ user.cpp:67: warning: left-hand operand of comma has no effect