Lab for CS112 Data Structures and Algorithms

Question

Answer this and please explain so that it is easy to understand the following questions and the explanation given.

Suppose the class D inherits from B. Which of the following assignments are legal?

B b;

D d;

B* pb;

D* pd;

a) b = d;

b) d = b;

c) pd = pb;

d) pb = pd;

e) d = pd;

f) b = *pd;

g) *pd = *pb;

Answer 1

Once again parent = child is legal, but child = parent is NOT

class B

{

public:

B() { }

};

class D : public B

{

public:

D() { }

};

int main()

{

B b;

D d;

B* pb;

D * pd;

b = d; // statement A is legal

d = b; //Compiler Error; cannot assign parent to child; Statement B is ILLEGAL !!!

pd = pb; //Compiler Error; cannot assign parent address to child address; Statement C is ILLEGAL !!!

pb = pd; // statement D is legal : assigns child address to parent address

d = pd; // statement E is ILLEGAL; type mismatch: object D vs pointer address

b = *pd; // statement F is legal; contents of child pointer can be assigned to parent object

*pd = *pb; // statement G is ILLEGAL; contents of parent pointer cannot be assigned to contents of child pointer

}