spider.cpp: In function 'void read()': spider.cpp:39: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result spider.cpp:42: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result spider.cpp: In function 'int main()': spider.cpp:86: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result spider.cpp:87: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result