foo.cc: In function 'void Output(std::vector<long long int>&)':
foo.cc:8:29: warning: comparison of integer expressions of different signedness: 'long long int' and 'std::vector<long long int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
    8 |         for(long long i=0; i<a.size(); i++)
      |                            ~^~~~~~~~~

[Hydro](https://hydro.ac)提供评测服务