foo.cc: In function 'void maxChar(std::string)':
foo.cc:6:11: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
    6 |  for(i=0;i<s.length();i++)
      |          ~^~~~~~~~~~~
foo.cc:8:9: warning: array subscript has type 'char' [-Wchar-subscripts]
    8 |   m[s[i]]++;
      |         ^

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