Compilare: user.cpp: In function ‘int main()’: user.cpp:25:23: warning: array subscript has type ‘char’ [-Wchar-subscripts] if(frec[sir[i]] == 0) ^ user.cpp:29:20: warning: array subscript has type ‘char’ [-Wchar-subscripts] frec[sir[i]] ++; ^ user.cpp:34:33: warning: array subscript has type ‘char’ [-Wchar-subscripts] frec[sir[st]]--; ^ user.cpp:36:36: warning: array subscript has type ‘char’ [-Wchar-subscripts] if(frec[sir[st]] == 0) ^