#include<iostream> 
using namespace std; 
class BB; 
class AA 
{ 
  private: 
  int v1; 
  public: 
   void setdata(int val) 
{ 
    v1=val; 
   } 
  int display() 
{ 
   return v1; 
  } 
  friend void exchange(AA &x,BB &y); 
}; 
class BB 
{ 
  private: 
  int v2; 
  public: 
  void setdata(int val) 
  { 
   v2=val; 
  } 
  int display() 
{ 
   return v2; 
  } 
  friend void exchange(AA &x,BB &y);  
}; 
void exchange(AA &x,BB &y) 
{ 
  int temp; 
  temp=x.v1; 
  x.v1=y.v2; 
  y.v2=temp; 
} 
int main() 
{ 
  AA a; 
  BB b; 
  try
  {
    a.setdata(10); 
    b.setdata(20); 
    cout<<"Before Exchange.."<<endl; 
    cout<<"a="<<a.display()<<endl; 
    cout<<"b="<<b.display()<<endl; 
    exchange(a,b); 
    cout<<"After Exchange.."<<endl; 
    cout<<"a="<<a.display()<<endl; 
    cout<<"b="<<b.display()<<endl;  
  }
  catch(const exception& e)
  {
    cerr << "An error occurred: " << e.what() << endl;
  }
  return 0; 
}