Main.cc:23:30: error: ISO C++ forbids declaration of ‘operator<’ with no type [-fpermissive] operator < (const node & b) const ^~~~~ Main.cc: In function ‘int main()’: Main.cc:58:12: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("div.in", "r", stdin); ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~ Main.cc:59:12: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("div.out", "w", stdout); ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~ Main.cc:60:10: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] scanf("%d %d", &n, &q); ~~~~~^~~~~~~~~~~~~~~~~ Main.cc:64:11: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] scanf("%d", &w); ~~~~~^~~~~~~~~~ Main.cc:72:14: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] scanf("%d %d", &x, &y); ~~~~~^~~~~~~~~~~~~~~~~