foo.cc: In function 'int main()':
foo.cc:10:23: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   10 |         for (int i=0;i<b.size();i++) {
      |                      ~^~~~~~~~~
foo.cc:11:23: warning: array subscript has type 'char' [-Wchar-subscripts]
   11 |                 t[b[i]]=1;
      |                       ^
foo.cc:13:19: warning: array subscript has type 'char' [-Wchar-subscripts]
   13 |         if (t[a[0]]) {
      |                   ^
foo.cc:18:23: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   18 |         for (int i=1;i<a.size();i++) {
      |                      ~^~~~~~~~~
foo.cc:19:27: warning: array subscript has type 'char' [-Wchar-subscripts]
   19 |                 if (t[a[i]]) {
      |                           ^
foo.cc:20:37: warning: array subscript has type 'char' [-Wchar-subscripts]
   20 |                         if (t[a[i-1]]==0) cout<<" ";
      |                                     ^

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