记住常量指针 和指针常量的区别

	int a = 5;
	int b = 19;
	int c = 27;
	int d = 44;
	//const int* p1 = &a;		//等同于p3 const在星花左侧叫常量指针
	//int const* p3 = &c;
	//p1 = &d;
	//p3 = &d;
	//*p1 = d;
	//*p3 = d;

	int* const p2 = &b;
	*p2 = d;
	p2 = &d;