grade.cpp: In function 'int main()': grade.cpp:8: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result grade.cpp:9: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result grade.cpp:11: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result grade.cpp:13: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result