void swapint(int &a,int &b) { int temp; temp=a; a=b; b=temp; }
c++自动把x,y的地址作为参数传递给swapint函数
int a = 1; int &b = a; b = 2; printf("a = %d ", a); //2
int a = 1; int *b = &a; *b = 2; printf("a = %d ", a); //2