Compilare: user.cpp: In function ‘int main()’: user.cpp:21:20: warning: array subscript has type ‘char’ [-Wchar-subscripts] freq[str[i]]++; ^ user.cpp:25:25: warning: array subscript has type ‘char’ [-Wchar-subscripts] if (!mark[str[i]]) { ^ user.cpp:26:62: warning: array subscript has type ‘char’ [-Wchar-subscripts] while (top > 0 && (str[i] < S[top] && freq[S[top]] >= 1)) { ^ user.cpp:27:28: warning: array subscript has type ‘char’ [-Wchar-subscripts] mark[S[top]] = 0; ^ user.cpp:31:24: warning: array subscript has type ‘char’ [-Wchar-subscripts] mark[S[top]] = 1; ^ user.cpp:32:24: warning: array subscript has type ‘char’ [-Wchar-subscripts] freq[str[i]]--; ^