foo.cc: In function ‘int cmp(std::string, std::string)’:
foo.cc:19:12: warning: array subscript has type ‘char’ [-Wchar-subscripts]
   19 | if (a[a1[i]]!=a[a2[i]]) return a[a1[i]]<a[a2[i]];
      |            ^
foo.cc:19:22: warning: array subscript has type ‘char’ [-Wchar-subscripts]
   19 | if (a[a1[i]]!=a[a2[i]]) return a[a1[i]]<a[a2[i]];
      |                      ^
foo.cc:19:39: warning: array subscript has type ‘char’ [-Wchar-subscripts]
   19 | if (a[a1[i]]!=a[a2[i]]) return a[a1[i]]<a[a2[i]];
      |                                       ^
foo.cc:19:48: warning: array subscript has type ‘char’ [-Wchar-subscripts]
   19 | if (a[a1[i]]!=a[a2[i]]) return a[a1[i]]<a[a2[i]];
      |                                                ^
foo.cc: In function ‘int main()’:
foo.cc:25:30: warning: array subscript has type ‘char’ [-Wchar-subscripts]
   25 | for (int i=0;i<26;i++) a[b[i]]=i;
      |                              ^