C++ Programming Questions and Answers – Friends

Here is a listing of C multiple choice questions on “Friends” along with answers, explanations and/or solutions:

1. Which rule will not affect the friend function?
a) private and protected members of a class cannot be accessed from outside
b) private and protected member can be accessed anywhere
c) both a & b
d) None of the mentioned
View Answer

Answer:a
Explanation:Friend is used to access private and protected members of a class from outside the same class.

2. Which keyword is used to declare the friend function?
a) firend
b) friend
c) classfriend
d) myfriend
View Answer

Answer:b
Explanation:None.

3. What is the syntax of friend function?
a) friend class1 Class2;
b) friend class;
c) friend class
d) None of the mentioned
View Answer

Answer:a
Explanation:In option a, the class2 is the friend of class1 and it can access all the private and protected members of class1.

4. What is the output of this program?

1.     #include <iostream>

2.     using namespace std;

3.     class Box

4.     {

5.         double width;

6.         public:

7.         friend void printWidth( Box box );

8.         void setWidth( double wid );

9.     };

10.     void Box::setWidth( double wid )

11.     {

12.         width = wid;

13.     }

14.     void printWidth( Box box )

15.     {

16.         box.width = box.width * 2;

17.         cout << "Width of box : " << box.width << endl;

18.     }

19.     int main( )

20.     {

21.         Box box;

22.         box.setWidth(10.0);

23.         printWidth( box );

24.         return 0;

25.    }

a) 40
b) 5
c) 10
d) 20
View Answer

Answer:d
Explanation:We are using the friend function for printwidth and multiplied the width value by 2, So we got the output as 20
Output:
$ g++ friend.cpp
$ a.out
20

5. What is the output of this program?

1.     #include <iostream>

2.     using namespace std;

3.     class sample 

4.     {

5.         int width, height;

6.         public:

7.         void set_values (int, int);

8.         int area () {return (width * height);}

9.         friend sample duplicate (sample);

10.     };

11.     void sample::set_values (int a, int b) 

12.     {

13.         width = a;

14.         height = b;

15.     }

16.     sample duplicate (sample rectparam)

17.     {

18.         sample rectres;

19.         rectres.width = rectparam.width * 2;

20.         rectres.height = rectparam.height * 2;

21.         return (rectres);

22.     }  

23.     int main ()  

24.     {

25.         sample rect, rectb;

26.         rect.set_values (2, 3);

27.         rectb = duplicate (rect);

28.         cout << rectb.area();

29.         return 0;

30.     }

a) 20
b) 16
c) 24
d) None of the mentioned
View Answer

Answer:c
Explanation:In this program, we are using the friend function for duplicate function and calculating the area of the rectangle.
Output:
$ g++ friend1.cpp
$ a.out
24

6. What is the output of this program?

1.     #include <iostream>

2.     using namespace std;

3.     class sample;

4.     class sample1 

5.     {

6.         int width, height;

7.         public:

8.         int area ()

9.         {

10.             return (width * height);}

11.             void convert (sample a);

12.         };

13.     class sample 

14.     {

15.         private:

16.         int side;

17.         public:

18.         void set_side (int a)

19.         { 

20.             side = a;

21.         }

22.         friend class sample1;

23.     };

24.     void sample1::convert (sample a) 

25.     {

26.         width = a.side;

27.         height = a.side;

28.     }

29.     int main () 

30.     {

31.         sample sqr;

32.         sample1 rect;

33.         sqr.set_side(6);

34.         rect.convert(sqr);

35.         cout << rect.area();

36.         return 0;

37.     }

a) 24
b) 35
c) 16
d) 36
View Answer

Answer:d
Explanation:In this program, we are using the friend for the class and calculating the area of the square.
Output:
$ g++ friend2.cpp
$ a.out
36

7. What is the output of this program?

1.     #include <iostream>

2.     using namespace std;

3.     class base

4.     {

5.         int val1, val2;

6.         public:

7.         int get()

8.  {

9.             val1 = 100;

10.             val2 = 300;

11.  }

12.         friend float mean(base ob);

13.     };

14.     float mean(base ob)

15.     {

16.         return float(ob.val1 + ob.val2) / 2;

17.     }

18.     int main()

19.     {

20.         base obj;

21.         obj.get();

22.         cout << mean(obj);

23.         return 0;

24.     }

a) 200
b) 150
c) 100
d) 300
View Answer

Answer:a
Explanation:In this program, We are finding the mean value by declaring the function mean as a friend of class base.
Output:
$ g++ friend3.cpp
$ a.out
200

8. What is the output of this program?

1.     #include <iostream>

2.     using namespace std;

3.     class sample

4.     {

5.         private:

6.         int a, b;

7.         public:

8.         void test()

9.         {

10.             a = 100;

11.             b = 200;

12.         }

13.         friend int compute(sample e1);

14.     };

15.     int compute(sample e1)

16.     {

17.         return int(e1.a + e1.b) - 5;

18.     }

19.     int main()

20.     {

21.         sample e;

22.         e.test();

23.         cout  << compute(e);

24.         return 0;

25.     }

a) 100
b) 200
c) 300
d) 295
View Answer

Answer:d
Explanation:In this program, we are finding a value from the given function by using the friend for compute function.
Output:
$ g++ friend4.cpp
$ a.out
295

9. Pick out the correct statement.
a) A friend function may be a member of another class.
b) A friend function may not be a member of another class.
c) A friend function may or may not be a member of another class.
d) None of the mentioned
View Answer

Answer:c
Explanation:None.

10. Where does keyword ‘friend’ should be placed?
a) function declaration
b) function definition
c) main function
d) None of the mentioned
View Answer

Answer:a
Explanation:The keyword friend is placed only in the function declaration of the friend function and not in the function definition because it is used toaccess the member of a class.