Compilare: user.cpp: In function ‘bool eval_num()’: user.cpp:58:30: warning: array subscript has type ‘char’ [-Wchar-subscripts] bool x = a[str[i]]; ^ user.cpp: In function ‘int main()’: user.cpp:76:12: warning: array subscript has type ‘char’ [-Wchar-subscripts] a[c] = !a[c]; ^ user.cpp:76:20: warning: array subscript has type ‘char’ [-Wchar-subscripts] a[c] = !a[c]; ^ user.cpp: In function ‘bool eval_num()’: user.cpp:65:1: warning: control reaches end of non-void function [-Wreturn-type] } ^