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:58:10: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] scanf("%d %d", &n, &q); ~~~~~^~~~~~~~~~~~~~~~~ Main.cc:62:11: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] scanf("%d", &w); ~~~~~^~~~~~~~~~ Main.cc:70:14: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] scanf("%d %d", &x, &y); ~~~~~^~~~~~~~~~~~~~~~~