foo.cc: In function ‘int checked(std::string, std::string)’:
foo.cc:20:30: warning: comparison of integer expressions of different signedness: ‘int’ and ‘std::__cxx11::basic_string<char>::size_type’ {aka ‘long unsigned int’} [-Wsign-compare]
   20 |         while (a[i]=='0' && i<a.size()) // 找 a的非 0位
      |                             ~^~~~~~~~~
foo.cc:24:30: warning: comparison of integer expressions of different signedness: ‘int’ and ‘std::__cxx11::basic_string<char>::size_type’ {aka ‘long unsigned int’} [-Wsign-compare]
   24 |         while (b[j]=='0' && j<b.size()) // 找 b的非 0位
      |                             ~^~~~~~~~~
foo.cc:28:14: warning: comparison of integer expressions of different signedness: ‘int’ and ‘std::__cxx11::basic_string<char>::size_type’ {aka ‘long unsigned int’} [-Wsign-compare]
   28 |         if (i==a.size())
      |             ~^~~~~~~~~~
foo.cc:51:1: warning: control reaches end of non-void function [-Wreturn-type]
   51 | }
      | ^