foo.cc: In function 'int main()':
foo.cc:11:20: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   11 |  for (int i = 0; i < s.length(); i++)
      |                  ~~^~~~~~~~~~~~
foo.cc:16:18: warning: comparison of integer expressions of different signedness: 'std::stack<char>::size_type' {aka 'long unsigned int'} and 'int' [-Wsign-compare]
   16 |    if (st.size() > maxdep)
      |        ~~~~~~~~~~^~~~~~~~

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