prime.cpp: In function 'int main()': prime.cpp:28: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result prime.cpp:29: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result prime.cpp:33: warning: ignoring return value of 'char* gets(char*)', declared with attribute warn_unused_result /tmp/ccUkM0mQ.o: In function `main': prime.cpp:(.text+0x195): warning: the `gets' function is dangerous and should not be used.