指针初始化

#include<iostream>
using namespace std;

class point
    {
        private:
        int x,y;
        public:
        void setpoint(int a,int b)
        {
            x=a;y=b;
        }   
        int getx()
        {
            return x;
        }
        int gety()
        {
            return y;   
        }   
    };

    int main()
    {

        point *op;
        op->setpoint(1,2);
        cout<<op->getx()<<endl;
        return 0;

    }
为啥不能运行呢？
另外“->”运算符号，与“.”运算符有什么区别？