foo.cc: In function 'int main()':
foo.cc:12:15: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   12 |  for(int i=0;i<str.length();i++)
      |              ~^~~~~~~~~~~~~
foo.cc:14:14: warning: comparison of integer expressions of different signedness: 'int' and 'std::stack<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   14 |   if(maxdepth<st.size())
      |      ~~~~~~~~^~~~~~~~~~

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