/in/foo.cc: In function 'int main()':
/in/foo.cc:12:9: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  while(i<a.size()&&j<b.size()) ans+=(a[i++]-'0')+(b[j++]-'0');
        ~^~~~~~~~~
/in/foo.cc:12:21: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  while(i<a.size()&&j<b.size()) ans+=(a[i++]-'0')+(b[j++]-'0');
                    ~^~~~~~~~~
/in/foo.cc:13:9: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  while(i<a.size()) ans+=a[i++]-'0';
        ~^~~~~~~~~
/in/foo.cc:14:9: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  while(j<b.size()) ans+=b[j++]-'0';
        ~^~~~~~~~~