foo.cc: In function 'int main()':
foo.cc:5:9: warning: unused variable 'k' [-Wunused-variable]
    5 |  int n, k = 0;
      |         ^
foo.cc:11:8: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
   11 |   scanf("%d", &a[i]);
      |   ~~~~~^~~~~~~~~~~~~
foo.cc:15:6: warning: 'b[0]' may be used uninitialized in this function [-Wmaybe-uninitialized]
   15 |  int max = b[0];
      |      ^~~

[Hydro](https://hydro.ac)提供评测服务