Question

Why declaration of two enums type with same values in same block is not allowed in C++?

enum math_students {A,B,C};
enum comp_students {D,E,A}; // illegal

Answer 1

C++03 enum doesn’t have tighter type checking under their scopes. So both math_students::A and comp_students::A can be simply referred as A. That’s why they are not allowed in the same scope.

To overcome that you can enclose them in namespace or class.

namespace math_students {
  enum { A, B, C };
}
namespace comp_students {
  enum { D, E, A };  // ok
}

In C++11 you can use enum class (it has tighter type checking; and they don’t get converted to int implicitly).

enum class math_students {A,B,C};
enum class comp_students {D,E,A};  // ok