foo.cc: In function 'void prime(int)':
foo.cc:8:23: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
    8 |     for (int i = 0; i < a.size(); i++)
      |                     ~~^~~~~~~~~~
foo.cc:12:23: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   12 |     for (int i = 0; i < a.size(); i++)
      |                     ~~^~~~~~~~~~
foo.cc:14:31: 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 = i + 1; j < a.size(); j++)
      |                             ~~^~~~~~~~~~
foo.cc:23:23: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   23 |     for (int i = 0; i < a.size(); i++)
      |                     ~~^~~~~~~~~~

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