foo.cc: In function ‘int main()’:
foo.cc:14:20: warning: comparison of integer expressions of different signedness: ‘long long int’ and ‘const std::__cxx11::basic_string<char>::size_type’ {aka ‘const long unsigned int’} [-Wsign-compare]
   14 |         while(index!=string::npos)
      |               ~~~~~^~~~~~~~~~~~~~
foo.cc:12:13: warning: unused variable ‘len’ [-Wunused-variable]
   12 |         int len = s.length();
      |             ^~~