Compilare: main.cpp: In function 'int main()': main.cpp:15:21: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i = 0;i < s.size();++i) ~~^~~~~~~~~~ main.cpp:16:16: warning: array subscript has type 'char' [-Wchar-subscripts] fr[s[i]]++; ^ main.cpp:20:15: warning: array subscript has type 'char' [-Wchar-subscripts] if(fr[c] == 1) ^ main.cpp:22:20: warning: array subscript has type 'char' [-Wchar-subscripts] else if(fr[c] > 1) ^