250+ TOP MCQs on C++ Friends and Answers

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) protected member can be accessed anywhere
d) private member can be accessed anywhere

Answer: a
Clarification: 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

Answer: b
Clarification: friend keyword is used to declare a friend function in C++.

3. What is the syntax of friend function?
a) friend class1 Class2;
b) friend class;
c) friend class
d) friend class()

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

4. What will be the output of the following C++ code?

```
    #include 
```
```
    using namespace std;
```
```
    class Box
```
```
    {
```
```
        double width;
```
```
        public:
```

        friend void printWidth( Box box );

```
        void setWidth( double wid );
```
```
    };
```
```
    void Box::setWidth( double wid )
```
```
    {
```
```
        width = wid;
```
```
    }
```
```
    void printWidth( Box box )
```
```
    {
```
```
        box.width = box.width * 2;
```

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

```
    }
```
```
    int main( )
```
```
    {
```
```
        Box box;
```
```
        box.setWidth(10.0);
```
```
        printWidth( box );
```
```
        return 0;
```
```
   }
```

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

Answer: d
Clarification: 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 will be the output of the following C++ code?

```
    #include 
```
```
    using namespace std;
```
```
    class sample
```
```
    {
```
```
        int width, height;
```
```
        public:
```
```
        void set_values (int, int);
```

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

        friend sample duplicate (sample);

```
    };
```

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

```
    {
```
```
        width = a;
```
```
        height = b;
```
```
    }
```
```
    sample duplicate (sample rectparam)
```
```
    {
```
```
        sample rectres;
```

        rectres.width = rectparam.width * 2;

        rectres.height = rectparam.height * 2;

```
        return (rectres);
```
```
    }
```
```
    int main ()
```
```
    {
```
```
        sample rect, rectb;
```
```
        rect.set_values (2, 3);
```
```
        rectb = duplicate (rect);
```
```
        cout << rectb.area();
```
```
        return 0;
```
```
    }
```

a) 20
b) 16
c) 24
d) 18

250+ TOP MCQs on Declaration and Answers

Answer: c
Clarification: 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 will be the output of the following C++ code?

```
    #include 
```
```
    using namespace std;
```
```
    class sample;
```
```
    class sample1
```
```
    {
```
```
        int width, height;
```
```
        public:
```
```
        int area ()
```
```
        {
```
```
            return (width * height);}
```
```
            void convert (sample a);
```
```
        };
```
```
    class sample
```
```
    {
```
```
        private:
```
```
        int side;
```
```
        public:
```
```
        void set_side (int a)
```
```
        {
```
```
            side = a;
```
```
        }
```
```
        friend class sample1;
```
```
    };
```
```
    void sample1::convert (sample a)
```
```
    {
```
```
        width = a.side;
```
```
        height = a.side;
```
```
    }
```
```
    int main ()
```
```
    {
```
```
        sample sqr;
```
```
        sample1 rect;
```
```
        sqr.set_side(6);
```
```
        rect.convert(sqr);
```
```
        cout << rect.area();
```
```
        return 0;
```
```
    }
```

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

Answer: d
Clarification: 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 will be the output of the following C++ code?

```
    #include 
```
```
    using namespace std;
```
```
    class base
```
```
    {
```
```
        int val1, val2;
```
```
        public:
```
```
        int get()
```
```
	{
```
```
            val1 = 100;
```
```
            val2 = 300;
```
```
	}
```
```
        friend float mean(base ob);
```
```
    };
```
```
    float mean(base ob)
```
```
    {
```

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

```
    }
```
```
    int main()
```
```
    {
```
```
        base obj;
```
```
        obj.get();
```
```
        cout << mean(obj);
```
```
        return 0;
```
```
    }
```

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

Answer: a
Clarification: 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 will be the output of the following C++ code?

```
    #include 
```
```
    using namespace std;
```
```
    class sample
```
```
    {
```
```
        private:
```
```
        int a, b;
```
```
        public:
```
```
        void test()
```
```
        {
```
```
            a = 100;
```
```
            b = 200;
```
```
        }
```
```
        friend int compute(sample e1);
```
```
    };
```
```
    int compute(sample e1)
```
```
    {
```
```
        return int(e1.a + e1.b) - 5;
```
```
    }
```
```
    int main()
```
```
    {
```
```
        sample e;
```
```
        e.test();
```
```
        cout  << compute(e);
```
```
        return 0;
```
```
    }
```

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

250+ TOP MCQs on Pointer to Function and Answers

Answer: d
Clarification: 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

Answer: c
Clarification: A friend function may or may not be a member of another class is the correct statement.

10. Where does keyword ‘friend’ should be placed?
a) function declaration
b) function definition
c) main function
d) block function

Answer: a
Clarification: 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.

250+ TOP MCQs on C++ Friends and Answers

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