Compilare: user.cpp: In function ‘int main()’: user.cpp:23:14: warning: array subscript has type ‘char’ [-Wchar-subscripts] frec[v[i]]++; ^ user.cpp:24:17: warning: array subscript has type ‘char’ [-Wchar-subscripts] if(frec[v[i]] == 1) ^ user.cpp:27:16: warning: array subscript has type ‘char’ [-Wchar-subscripts] frec[v[x]]--; ^ user.cpp:28:19: warning: array subscript has type ‘char’ [-Wchar-subscripts] if(frec[v[x]] == 0){ ^