/in/foo.cc: In function 'void fenjie(int)':
/in/foo.cc:19:22: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   19 |         for(int i=0;i<prime.size();i++)
      |                     ~^~~~~~~~~~~~~
/in/foo.cc: In function 'int main()':
/in/foo.cc:45:30: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   45 |                 for(int j=0;j<prime.size()&&i*prime[j]<=N;j++)
      |                             ~^~~~~~~~~~~~~