foo.cc: In function 'int main()':
foo.cc:18:20: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   18 |  for (int i = 0; i < a.length(); i++) {
      |                  ~~^~~~~~~~~~~~
foo.cc:16:6: warning: unused variable 'ans' [-Wunused-variable]
   16 |  int ans = 0;
      |      ^~~

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