gray.cpp: In function 'int main()': gray.cpp:151: warning: unused variable 'i' gray.cpp:149: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result gray.cpp:150: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result gray.cpp:154: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result