foo.cc: In function 'int main()':
foo.cc:38:13: warning: statement has no effect [-Wunused-value]
   38 |         for(j;j<nb;j++)
      |             ^
foo.cc:43:13: warning: statement has no effect [-Wunused-value]
   43 |         for(i;i<na;i++)
      |             ^
foo.cc:46:14: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   46 |     for(i=0;i<c.size();i++)
      |             ~^~~~~~~~~

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