/in/foo.cc: In member function 'Wint& Wint::check()':
/in/foo.cc:21:27: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
         for (int i = 1; i < size(); ++i) {
                         ~~^~~~~~~~
/in/foo.cc: In function 'Wint& operator+=(Wint&, const Wint&)':
/in/foo.cc:80:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     for (int i = 0; i != b.size(); ++i)a[i] += b[i];
                     ~~^~~~~~~~~~~
/in/foo.cc: In function 'Wint& operator-=(Wint&, Wint)':
/in/foo.cc:90:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     for (int i = 0; i != b.size(); a[i] -= b[i], ++i)
                     ~~^~~~~~~~~~~
/in/foo.cc: In function 'Wint operator*(const Wint&, const Wint&)':
/in/foo.cc:110:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     for (int i = 0; i != a.size(); ++i)
                     ~~^~~~~~~~~~~
/in/foo.cc:111:27: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
         for (int j = 0; j != b.size(); ++j)
                         ~~^~~~~~~~~~~