foo.cc: In member function 'void gjd::Add(std::vector<int>&)':
foo.cc:18:10: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   while(i<v.size()&&i<v2.size())
         ~^~~~~~~~~
foo.cc:18:22: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   while(i<v.size()&&i<v2.size())
                     ~^~~~~~~~~~
foo.cc:25:10: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   while(i<v.size())
         ~^~~~~~~~~
foo.cc:32:10: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   while(i<v2.size())
         ~^~~~~~~~~~
foo.cc: In member function 'void gjd::Sub(std::vector<int>)':
foo.cc:48:10: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   while(i<v.size()&&i<v1.size())
         ~^~~~~~~~~
foo.cc:48:22: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   while(i<v.size()&&i<v1.size())
                     ~^~~~~~~~~~
foo.cc: In member function 'void gjd::Mul(int)':
foo.cc:68:10: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   while(i<v.size())
         ~^~~~~~~~~
foo.cc: In member function 'int gjd::Sum()':
foo.cc:97:16: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   for(int i=0;i<v.size();i++)
               ~^~~~~~~~~
foo.cc: In function 'int main()':
foo.cc:119:47: warning: suggest parentheses around '&&' within '||' [-Wparentheses]
  if(y1.CanDiv(6)||y2.CanDiv(6)||y3.v.size()==1&&(y3.v[0]==2||y3.v[0]==3))
                                 ~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~

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