foo.cc: In function 'int main()':
foo.cc:39:18: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   39 |     for(int i=1;i<v.size();i++)
      |                 ~^~~~~~~~~
foo.cc:26:10: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
   26 |     scanf("%d%d",&a,&b);
      |     ~~~~~^~~~~~~~~~~~~~

[Hydro](https://hydro.ac)提供评测服务