Compilare: main.cpp: In function 'int main()': main.cpp:12:18: warning: comparison of integer expressions of different signedness: 'int' and 'std::__cxx11::basic_string<char>::size_type' {aka 'long unsigned int'} [-Wsign-compare] 12 | for(int i=0;i<s.size();i++) | ~^~~~~~~~~ main.cpp:14:15: warning: array subscript has type 'char' [-Wchar-subscripts] 14 | f[s[i]]++; | ^ main.cpp:15:18: warning: array subscript has type 'char' [-Wchar-subscripts] 15 | if(f[s[i]]==2) | ^ main.cpp:17:18: warning: array subscript has type 'char' [-Wchar-subscripts] 17 | if(f[s[i]]==1) | ^