不允许创建临时变量，交换两个数值

#include <stdio.h>
#include<stdlib.h>
void main()
{
	int a = 1;
	int b = 2;
	printf("a=%d,b=%d\n", a, b);
	a = a + b; 
	b = a - b;      //此时b中放着a的值
	a = a - b;      
	printf("a=%d,b=%d\n", a, b);
	system("pause");
}