/in/foo.cc: In member function 'bign& bign::check()':
/in/foo.cc:13:17: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   for(int i=1; i<size(); ++i) {
                ~^~~~~~~
/in/foo.cc: In function 'bign& operator+=(bign&, const bign&)':
/in/foo.cc:62:16: 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 'bign& operator-=(bign&, bign)':
/in/foo.cc:70:16: 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 'bign operator*(const bign&, const bign&)':
/in/foo.cc:87:16: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(int i=0; i!=a.size(); ++i)
               ~^~~~~~~~~~
/in/foo.cc:88:17: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   for(int j=0; j!=b.size(); ++j)
                ~^~~~~~~~~~