/in/foo.cc: In function 'int main()':
/in/foo.cc:34:14: warning: array subscript has type 'char' [-Wchar-subscripts]
     if (vis[c]) ce=1;
              ^
/in/foo.cc:36:10: warning: array subscript has type 'char' [-Wchar-subscripts]
     vis[c]=1;
          ^
/in/foo.cc:62:17: warning: array subscript has type 'char' [-Wchar-subscripts]
     vis[stc[top]]=0;
                 ^