不定义临时变量情况下，交换两个变量的值

 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 }