int *p1 = &x; //p1指向x的地址
int *p2 = &y; //p2指向y的地址
p2 = p1; //p1,p2都指向了x的地址
*p1 = *p1 + *p2; //相當於(X)=X+X
*p2 = *p1 - *p2; //相當於(X)=X-X
printf("%d,%d", x, y);