1.      Program to swap private data members of classes named `class1` and `class2` using a friend function.

1. #include <iostream.h>

2. #include<conio.h>

3. class class2;

4.  

5. class class1 {

6. private:

7.     int x;

8.  

9. public:

10.     class1(int x) : x(x) {}

11.  

12.     friend void swap(class1& obj1, class2& obj2);

13.  

14.     void print() {

15.         cout << "Class1: " << x << endl;

16.     }

17. };

18.  

19. class class2 {

20. private:

21.     int y;

22.  

23. public:

24.     class2(int y) : y(y) {}

25.  

26.     friend void swap(class1& obj1, class2& obj2);

27.  

28.     void print() {

29.         cout << "Class2: " << y << endl;

30.     }

31. };

32.  

33. void swap(class1& obj1, class2& obj2) {

34.     int temp = obj1.x;

35.     obj1.x = obj2.y;

36.     obj2.y = temp;

37. }

38.  

39. int main() {

40.     class1 obj1(10);

41.     class2 obj2(20);

42.  

43.     cout << "Before swapping:\n";

44.     obj1.print();

45.     obj2.print();

46.  

47.     swap(obj1, obj2);

48.  

49.     cout << "\nAfter swapping:\n";

50.     obj1.print();

51.     obj2.print();

52.     getch();

53.     return 0;

55. }