foo.cc: In function 'int countChar(std::string, char)':
foo.cc:6:20: 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 (int i = 0; i < s.length(); i++)
      |                  ~~^~~~~~~~~~~~
foo.cc: In function 'int main()':
foo.cc:17:6: warning: unused variable 't' [-Wunused-variable]
   17 |  int t, i, n, len = 0, rk = 0;
      |      ^

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