/in/foo.cc: In function 'int main()':
/in/foo.cc:19:21: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   for (int i = 0; i < a.length(); i++)
                   ~~^~~~~~~~~~~~
/in/foo.cc:30:21: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   for (int i = 0; i < a.length(); i++)
                   ~~^~~~~~~~~~~~
/in/foo.cc:13:7: warning: unused variable 'cnt' [-Wunused-variable]
   int cnt[5]{ 0 };
       ^~~