foo.cc: In member function 'Wint& Wint::check()':
foo.cc:16:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
         for(int i=1; i<size(); ++i)
                      ~^~~~~~~
foo.cc: In function 'Wint& operator+=(Wint&, const Wint&)':
foo.cc:79:19: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     for(int i=0; i!=b.size(); ++i)a[i]+=b[i];
                  ~^~~~~~~~~~
foo.cc: In function 'Wint& operator-=(Wint&, Wint)':
foo.cc:90:19: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     for(int i=0; i!=b.size(); a[i]-=b[i],++i)
                  ~^~~~~~~~~~
foo.cc: In function 'Wint operator*(const Wint&, const Wint&)':
foo.cc:112:19: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     for(int i=0; i!=a.size(); ++i)
                  ~^~~~~~~~~~
foo.cc:113:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
         for(int j=0; j!=b.size(); ++j)
                      ~^~~~~~~~~~

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