foo.cc: In function ‘int main()’:
foo.cc:14:22: warning: comparison of integer expressions of different signedness: ‘int’ and ‘std::vector<int>::size_type’ {aka ‘long unsigned int’} [-Wsign-compare]
   14 |         for(int j=0;j<prime.size() && i*prime[j]<=n;j++)
      |                     ~^~~~~~~~~~~~~
foo.cc:20:18: warning: comparison of integer expressions of different signedness: ‘int’ and ‘std::vector<int>::size_type’ {aka ‘long unsigned int’} [-Wsign-compare]
   20 |     for(int i=0;i<prime.size();i++) cout<<prime[i]<<" ";
      |                 ~^~~~~~~~~~~~~
foo.cc:10:9: warning: unused variable ‘p’ [-Wunused-variable]
   10 |     int p=0;
      |         ^