Compilare: user.cpp: In function ‘int main()’: user.cpp:13:20: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int x = 0;x<n.length();x++){ ~^~~~~~~~~~~ user.cpp:14:19: warning: array subscript has type ‘char’ [-Wchar-subscripts] if(!c[n[x]]){ ^ user.cpp:15:19: warning: array subscript has type ‘char’ [-Wchar-subscripts] c[n[x]] = true; ^ user.cpp:19:18: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int x = 0; x<n.length(); x++) ~^~~~~~~~~~~ user.cpp:22:18: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int x = 0; x<n.length(); x++) { ~^~~~~~~~~~~