foo.cc: In function 'int main()':
foo.cc:8:27: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
    8 |         for (int i = 0; i < s.size(); i++)
      |                         ~~^~~~~~~~~~
foo.cc:9:25: warning: array subscript has type 'char' [-Wchar-subscripts]
    9 |                 cnt[s[i]]++;
      |                         ^
foo.cc:10:27: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   10 |         for (int i = 0; i < s.size(); i++)
      |                         ~~^~~~~~~~~~
foo.cc:11:29: warning: array subscript has type 'char' [-Wchar-subscripts]
   11 |                 if (cnt[s[i]] == 1)
      |                             ^

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