Compilare: user.cpp: In function ‘int main()’: user.cpp:23:16: warning: array subscript has type ‘char’ [-Wchar-subscripts] if (!f[str[i]]) { ^ user.cpp:26:11: warning: array subscript has type ‘char’ [-Wchar-subscripts] f[str[i]]+= 1; } ^ user.cpp: In lambda function: user.cpp:29:13: warning: array subscript has type ‘char’ [-Wchar-subscripts] return f[a] < f[b]; }); ^ user.cpp:29:20: warning: array subscript has type ‘char’ [-Wchar-subscripts] return f[a] < f[b]; }); ^ user.cpp: In function ‘int main()’: user.cpp:41:23: warning: array subscript has type ‘char’ [-Wchar-subscripts] str[i] = del[str[i]] ? '*' : str[i]; ^ user.cpp:56:19: warning: array subscript has type ‘char’ [-Wchar-subscripts] del[deletion[it]] = true; } ^