type compatiblity in c and c++

Name type compatibility means two variables are compatible only if they are declared together, or with the same type. Example:
compatible

int a, b;

incompatible

int number;
string name;

Structure type compatibility means two variables are compatible if they have the same structure. This is harder to define, because you can have the same structure but different fields.

struct A
{
int a;
int b;
};

struct B
{
int Count;
int Index;
};

On the other hand, a and b below should be compatible:

typedef int Age;

Age a;
int b;

C uses structural compatibility for all types except structures and unions, where it uses declaration equivalence.