C++ inheritance: scoping and visibility of members

Question

Can you explain why this is not allowed,

#include <stdio.h>

class B {
private:
    int a;
public:
    int a;
};

int main() {
    return 0;
}

while this is?

#include <stdio.h>

class A {
public:
    int a;
};

class B : public A{
private:
    int a;
};

int main() {
    return 0;
}

In both the cases, we have one public and one private variable named a in class B.

---

edited now!

Answer 1

In both the cases, we have one public and one private variable named a in class B.

No, thats not true.

In the first case, you can't have two identifiers with the same name in the same scope. While in the second case, B::a hides A::a, and to access A::a you have to fully qualify the name:

b.a = 10; // Error. You can't access a private member.
b.A::a = 10; // OK.