foo.cc: In function 'int main()':
foo.cc:13:109: warning: format '%s' expects argument of type 'char*', but argument 2 has type 'char (*)[30]' [-Wformat=]
  for (int i = 0; scanf("%s %d %d %d %d %d", &stu[i].a, &stu[i].b, &stu[i].c, &stu[i].d, &stu[i].e, &stu[i].f) != EOF;) {
                                             ~~~~~~~~~                                                       ^
foo.cc:9:6: warning: variable 'temp' set but not used [-Wunused-but-set-variable]
  int temp;
      ^~~~
foo.cc:12:7: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
  scanf("%d", &n);
  ~~~~~^~~~~~~~~~

[Hydro](https://hydro.ac)提供评测服务