pento.cpp: In function 'void backt()': pento.cpp:515: warning: unused variable 'l' pento.cpp: In function 'int main()': pento.cpp:552: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result pento.cpp:553: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result pento.cpp:557: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result pento.cpp:560: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result