谁看下我错哪了，一开始输入0后就出错！！peach5460在吗，给分的机会到了

#include <iostream>
#include<string>
using namespace std;

class book
{
public:
    int num;
    float price;
    book * next;
};

book *head=NULL;
bool check(string str)
{
    for(int i=0;i<str.length();i++)
    {
        if ((str[i]<'0'||str[i]>'9' )&& (str[i]!='.'))
        {
   
            return false;
        }
    }
    return true;
}

book * creat()
{
   
    book * pone;
    book * ptwo;
    pone=new book;
    ptwo=pone;
    head=pone;
    cout<<"输入图书编号以0结束"<<endl;
    string str;
    cin>>str;
    while (!check(str))
    {
        cout<<"你输入的不是数字，请输入数字"<<endl;
        cin>>str;
    }
    pone->num=atoi(str.c_str());
        
    if(pone->num!=0)
    {
        cout<<"请输入图书的价格:"<<endl;
            cin>>str;
    while (!check(str))
    {
        cout<<"你输入的不是数字，请输入数字"<<endl;
        cin>>str;
    }
    pone->price=atof(str.c_str());
   
    }
    else
    {
        delete pone;ptwo=NULL;ptwo->next=NULL;head=NULL;return head;
    }
    while (pone->num!=0)
    {
      ptwo=pone;
      pone=new book;
      cout<<"输入图书编号以0结束"<<endl;
      cin>>str;
    while (false==check(str))
    {
        cout<<"你输入的不是数字，请输入数字"<<endl;
        cin>>str;
    }
    pone->num=atoi(str.c_str());
    if(pone->num!=0)
    {
        cout<<"请输入图书的价格:"<<endl;
        cin>>str;
    while (false==check(str))
    {
        cout<<"你输入的不是数字，请输入数字"<<endl;
        cin>>str;
    }
    pone->price=atof(str.c_str());
   
    }
   

   
    }

        delete pone;            
        pone->next=NULL;
        return head;
}
int main()
{
    creat();
    return 0;
}
要讲清楚呦，本人比较笨的