foo.cc: In function ‘int main()’:
foo.cc:15:19: warning: comparison of integer expressions of different signedness: ‘int’ and ‘std::vector<int>::size_type’ {aka ‘long unsigned int’} [-Wsign-compare]
   15 |         while(flag<Prime.size()&&i*Prime[flag]<=n)
      |               ~~~~^~~~~~~~~~~~~
foo.cc:23:18: warning: comparison of integer expressions of different signedness: ‘int’ and ‘std::vector<bool>::size_type’ {aka ‘long unsigned int’} [-Wsign-compare]
   23 |     for(int i=0;i<v.size();i++)
      |                 ~^~~~~~~~~