foo.cc: In function 'void Output(std::vector<int>&)':
foo.cc:5:19: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     for(int i=0; i<v.size(); i++)
                  ~^~~~~~~~~
foo.cc: In function 'void FindAsc(std::vector<int>&, std::vector<int>&)':
foo.cc:28:18: 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:44:17: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     for(i=0; i+2<si.size(); i+=2)
              ~~~^~~~~~~~~~

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