foo.cc: In function ‘void add()’:
foo.cc:9:23: warning: comparison of integer expressions of different signedness: ‘int’ and ‘std::vector<short int>::size_type’ {aka ‘long unsigned int’} [-Wsign-compare]
    9 |         for (i = 0; i < ans.size(); i++)
      |                     ~~^~~~~~~~~~~~
foo.cc: In function ‘int main()’:
foo.cc:45:23: warning: comparison of integer expressions of different signedness: ‘int’ and ‘std::vector<int>::size_type’ {aka ‘long unsigned int’} [-Wsign-compare]
   45 |         for (i = 0; i < prime.size(); i++)
      |                     ~~^~~~~~~~~~~~~~