virus.cpp: In function 'void read()': virus.cpp:20: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result virus.cpp:21: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result virus.cpp:23: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result virus.cpp:24: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result virus.cpp:26: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result virus.cpp:27: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result