Compilare: user.cpp: In function ‘int main()’: user.cpp:33:9: warning: array subscript has type ‘char’ [-Wchar-subscripts] v[s[i]].pb(i); ^ user.cpp:45:34: warning: array subscript has type ‘char’ [-Wchar-subscripts] auto it = lower_bound(v[letter].begin(), v[letter].end(), last); ^ user.cpp:45:53: warning: array subscript has type ‘char’ [-Wchar-subscripts] auto it = lower_bound(v[letter].begin(), v[letter].end(), last); ^ user.cpp:49:36: warning: array subscript has type ‘char’ [-Wchar-subscripts] if (other != letter && *v[other].rbegin() < *it) { ^