foo.cc: In function 'void add(int)':
foo.cc:13:15: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   13 |  for(int i=0;i<=sum.length()-1;i++)
      |              ~^~~~~~~~~~~~~~~~
foo.cc: In function 'void dfs(int, int)':
foo.cc:45:11: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   45 |  for(i=0;i<p[u].son.size();i++)
      |          ~^~~~~~~~~~~~~~~~
foo.cc: In function 'void dfs2(int, int)':
foo.cc:57:11: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   57 |  for(i=0;i<p[u].son.size();i++)
      |          ~^~~~~~~~~~~~~~~~
foo.cc: In function 'int main()':
foo.cc:112:6: warning: statement has no effect [-Wunused-value]
  112 |  for(i;i<=out.length()-1;i++)
      |      ^
foo.cc:112:9: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
  112 |  for(i;i<=out.length()-1;i++)
      |        ~^~~~~~~~~~~~~~~~

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