Friend function in c++:

class miles;

class km

 {

   float value;

   public :

  // void input();

    km convert(km  ,int a ) ;

   void output()

   {

   cout << value;

   }

  };

                                km km :: convert(km a,int b)

                                {

                                a.value = b * 1.61;

                                return a;

                                }

                class miles

                  {

                   int value;

                   public:

                   void input()

                   {

                   cout << "Enter the value\n";

                  cin >> value;

                   }

                   friend km & convert(km &,miles);

                   };

                km & convert(km & a,miles b)

                                {

                                a= b.value * 1.61;

                                return a;

                                }

   void main()

   {

     km a;

     miles b;

      clrscr();

     b.input();

     a= convert (a,b);

     a.output();

     getch();

    }