1 #include <iostream> 2 using namespace std; 3  4  5 void swap(int& x,int& y) 6 { 7     y = x + y; 8     x = y - x; 9     y = y - x;10 }11 12 int _tmain(int argc, _TCHAR* argv[])13 {14     int a = 10, b=20;15     cout << "before swap: a= "<<a <<" b= "<<b<<endl;16 17     swap(a,b);18     cout <<"after  swap: a= "<<a << " b= "<<b<<endl;19 20     return 0;21 }