Compilare: main.cpp: In function 'int main()': main.cpp:37:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for (int i = 0; i < s.size(); ++i) { ~~^~~~~~~~~~ main.cpp:38:18: warning: array subscript has type 'char' [-Wchar-subscripts] ++fv[s[i]]; ^ main.cpp:39:20: warning: array subscript has type 'char' [-Wchar-subscripts] if (fv[s[i]] == 1) ^ main.cpp:41:25: warning: array subscript has type 'char' [-Wchar-subscripts] else if (fv[s[i]] == 2) ^