foo.cc: In function 'int main()':
foo.cc:7:22: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
    7 |         for(int i=0;i<s.size();i++)
      |                     ~^~~~~~~~~
foo.cc:16:17: error: 'else' without a previous 'if'
   16 |                 else
      |                 ^~~~