#include<iostream>
int i = 3, * pd = &i;
int main(){
    //int *pd = nullptr;
    std::cout<<"此时*pd的值是: "<<*pd<<" pd的值是:"<<pd<<std::endl;
    *pd = 4;
    std::cout <<"在*pd=4之后,i的值是:"<< i <<" pd的值是: "<<pd<< std::endl;
    pd = 0;
    std::cout <<"在pd=0之后,i的值是:"<< i << " pd的值是:" << pd << std::endl;
    //std::cout << "最后,pd和*pd分别为: " << pd << " " << *pd << std::endl;
    //上面是错误的,当pd设置内存地址为0的时候,再去读*pd,实际是读取pd这个内存地址里的东西,而系统是不允许读取这个地址的
    return 0;
}