foo.cc: In function 'int main()':
foo.cc:42:15: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(int i=0;i<a[0].size();i++) cout<<a[0][i]<<" ";
              ~^~~~~~~~~~~~
foo.cc:44:15: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(int i=0;i<a[1].size();i++) cout<<a[1][i]<<" ";
              ~^~~~~~~~~~~~

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