数值交换算法
三种方法：(1)使用临时变量 (2)不使用中间变量，仅使用加法运算 (3)不使用中间变量，使用异或XOR操作
#include <iostream.h>template <typename T>void swap_var(T &a, T &b){? T tmp;? tmp = a;? a = b;? b = tmp;}

template <typename T>void swap_add(T &a, T &b){? a = a - b;? b = a + b;? a = b - a;}

template <typename T>void swap_xor(T &a, T &b){? a = a ^ b;? b = b ^ a;? a = a ^ b;}

int main(int argc, char *argv[]){? int a, b;? a = atoi(argv[1]);? b = atoi(argv[2]);? swap_var(a, b);? cout<<"swap_var: a="<<a<<", b="<<b<<endl;? swap_add(a, b);? cout<<"swap_add: a="<<a<<", b="<<b<<endl;? swap_xor(a, b);? cout<<"swap_xor: a="<<a<<", b="<<b<<endl;}