/in/foo.cc: In function 'void std::writef(double, int)':
/in/foo.cc:65:24: warning: array subscript has type 'char' [-Wchar-subscripts]
      while (x) s_[++top] = x % 10, x /= 10;
                        ^
/in/foo.cc:66:34: warning: array subscript has type 'char' [-Wchar-subscripts]
      while (top) *p3++ = s_[top--] ^ '0';
                                  ^
/in/foo.cc: In function 'void std::write(Tp)':
/in/foo.cc:92:24: warning: array subscript has type 'char' [-Wchar-subscripts]
      while (x) s_[++top] = x % 10, x /= 10;
                        ^
/in/foo.cc:93:34: warning: array subscript has type 'char' [-Wchar-subscripts]
      while (top) *p3++ = s_[top--] ^ '0';
                                  ^