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 Sub is derived from the class Sandwich. Which of the following assignments are legal?

a) Sandwich* x = new Sandwich(); a) Sub* y = new Sub();

b) x = y;

c) y = x;

d) y = new Sandwich();

e) x = new Sub(); f) *x = *y; g) *y = *x;

Answer 1

The main rule of thumb here is that the child CAN be assigned to the PARENT, but not vice versa.

class Sandwich

{

public :

Sandwich()

{

}

};

class Sub : public Sandwich

{

public :

Sub()

{

}

};

int main()

{

// option A : properly declares and initializes pointers to the Sandwhich and Sub objects

Sandwich * x = new Sandwich();

Sub * y = new Sub();

// option A is correct and legal

//option B: both pointers point at the sub

x = y;

// option B is correct and legal; Child can be assigned to parent

// y=x; //COMPILER ERROR: cannot assign parent to child opton C is ILLEGAL !!!

// y = new Sandwich(); //COMMPILER ERROR: child object pointer cannot contain address of parent object

// option D is ILLEGAL !!!

x = new Sub(); // Address of child can be asigned to pointer to Parent;

// option E is legal

*x = *y; // child object can be assigned to parent object; option F is legal

*y = *x; // COMPILER ERROR: cannot assign parent to child

// option G is ILLEGAL !!!

}