foo.cc: In function 'int main()':
foo.cc:24:21: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   24 |   for (int j = 0; j < pr.size() && pr[j] * i < n; j++)
      |                   ~~^~~~~~~~~~~
foo.cc:30:20: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   30 |  for (int i = 0; i < pr.size(); i++)
      |                  ~~^~~~~~~~~~~

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