CSCI 152 Quiz 6 ( May 3 ) Name _______________________

Spring 2005

1. Circle the correct answer, true or false, for the following questions:

True	False	The three basic principles of Object-Oriented Design are encapsulation, inheritance and polymorphism.
True	False	Inheritance is an “is-a” relation.
True	False	C++ does not support multiple inheritance (the ability for a class to be derived from 2 or more base classes).
True	False	Private members of a base class are private to the base class. The derived class cannot directly access them.
True	False	Classes may not be data members of other classes.
True	False	A derived class can not redefine the function members of a base class.
True	False	The public members of a base class can be inherited either as public or private by the derived class.
True	False	A pointer is a variable that contains the address of another variable as its value.
True	False	Increment (++) and decrement (--) operators are allowed on pointer variables.
True	False	The address of operator (&) returns the value pointed to by a pointer.
True	False	If p is a pointer variable, then the statement p = p * 2; is valid in C++.
True	False	In C++, pointer variables are declared using the reserved word pointer.

2. In 2 or 3 sentences, explain the difference between the private and protected members of a class.

Private members are private, even for classes derived from the class. Protected members are private to clients of a class, but are accessible (e.g. seem like they are public) to derived classes.

3. Consider the following statements:

class yClass

{

public:

void one();

void two(int, int);

yClass();

private:

int a;

int b;

};

class xClass: public yClass

{

public:

void one();

xClass();

private:

int z;

}

yClass y;

xClass x;

a. The private members of yClass are public members of xClass. True or False?

b. Mark the following statements as valid or invalid. If a statement is invalid, explain why.

(i) valid

void yClass::one()

{

cout << a+b << endl;

}

(ii) invalid, members a & b are private

y.a = 15;

x.b = 30;

(iii) invalid, a&b are private, not accessible to derived xClass

void xClass::one()

{

a = 10;

b = 15;

z = 30;

cout << a + b + z << endl;

}

(iv) invalid, same as ii, a & b are private

cout << y.a << “ “ << y.b << “ “ << x.z << endl;

(-still using the class declarations for problem #3, previous page-)

c. Write the definition of the default constructor of yClass so that the private data members of yClass are initialized to 0.

yClass::yClass()

{

a = 0;

b = 0;

}

d. Write the definition of the default constructor of xClass so that the private data members of xClass are initialized to 0.

xClass::xClass()

{

z = 0;

}

e. Write the definition of the member function two of yClass so that the private data member a is initialized to the value of the first parameter of two, and the private data member b is initialized to the value of the second parameter of two.

void yClass::two(int p1, int p2)

{

a = p1;

b = p2;

}

4. Given the declarations:

int x;

int *p;

int *q;

Mark the following statements as valid or invalid. If a statement is invalid, explain why.

a. p = q; valid

b. *p = 56; valid (or invalid if you say that p and q have not been initialized yet)

c. p = x; invalid, always invalid to assign something of type int to something of type int*

d. *p = *q; valid (or invalid again if you assume p & q have not been initialized so they point to random garbage)

e. q = &x; valid, always valid to assign a pointer to point to an address of a variable of the correct type

f. *p = q; invalid, always invalid to assign an integer (dereferencing p using *p means it is an integer value) to have an address (q contents are a memory address, whatever it is pointing to)

5. What is the output of the following C++ code?

int x;

int y;

int *p = &x;

int *q = &y;

*p = 35;

*q = 98;

*p = *q;

cout << x << “ “ << y << endl;

cout << *p << “ “ << *q << endl;

98 98

98 98

6. What is the output of the following C++ code?

int x;

int *p;

int *q;

p = new int[10];

q = p;

*p = 4;

for (int j=0; j<10; j++)

{

x = *p;

p++;

*p = x + j;

}

for (int k=0; k < 10; k++)

{

cout << *q << “ “;

q++;

}

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