C++删除链表，高手进

#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]>'9'||str[i]<'0')&&(str[i]!='.'))
return false;
}
return true;
}
book *creat()
{
book *p1,*p2;
p1=new book;
head=p1;
p2=p1;
cout<<"请输入图书的编号，以0结束"<<endl;
string str;
cin>>str;
while(!check(str))
{
cout<<"刚才输入的不是数字，请重新输入，按0返回！！！"<<endl;
cin>>str;
}
p1->num=atoi(str.c_str());
if(p1->num!=0)
{
cout<<"请输入图书的价格"<<endl;
cin>>str;
while(!check(str))
{
cout<<"刚才输入的不是数字，请重新输入，按0返回！！！"<<endl;
cin>>str;
}
p1->price=atof(str.c_str());
}
else
{
delete p1;
p2=NULL;
p2->next=NULL;
head=NULL;
return head;
}
while(p1->num!=0)
{
p2=p1;
p1=new book;
cout<<"请输入图书的编号，以0结束"<<endl;
cin>>str;
while(!check(str))
{
cout<<"刚才输入的不是数字，请重新输入，按0返回！！！"<<endl;
cin>>str;
}
p1->num=atoi(str.c_str());
if(p1->num!=0)
{
cout<<"请输入图书的价格"<<endl;
cin>>str;
while(!check(str))
{
cout<<"刚才输入的不是数字，请重新输入，按0返回！！！"<<endl;
cin>>str;
}
p1->price=atof(str.c_str());
}
p2->next=p1;
}
delete p1;
p2->next=NULL;
return head;
}
void showbook(book *head)
{
cout<<endl;
cout<<"图书信息如下："<<endl;
while(head)
{
cout<<"图书编号："<<head->num<<"\t";
cout<<"价格："<<head->price<<endl;
head=head->next;
}
}
void Delete(book *head,int num)
{
book *l;
if(head->num==num)
{
l=head;
head=head->next;
::head=head;
delete l;
cout<<"操作成功"<<endl;
return;
}
while(head)
{
if(head->next==NULL)
{
cout<<"找不到要删除的编号。"<<endl;
return;
}
if(head->next->num==num)
{
l=head->next;
head->next=l->next;
delete l;
cout<<"操作成功"<<endl;
return;
}
head=head->next;
}
cout<<"找不到要删除的编号。"<<endl;
}
int main()
{
book *head=NULL;
head=creat();
showbook(head);
cout<<"请输入要删除的编号：";
int BookNum;
cin>>BookNum;
Delete(head,BookNum);
showbook(head);
return 0;
}

____________________________________________________________

删除中间和最后元素没问题 只有删除头元素出现内存错误

求高手指教

定义了两个head指针，请见量，我自己也很混乱

#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]>'9'||str[i]<'0')&&(str[i]!='.'))
return false;
}
return true;
}

book *creat()
{
book *p1,*p2;
p1=new book;
head=p1;
p2=p1;
cout<<"请输入图书的编号，以0结束"<<endl;
string str;
cin>>str;

while(!check(str))
{
cout<<"刚才输入的不是数字，请重新输入，按0返回！！！"<<endl;
cin>>str;
}

p1->num=atoi(str.c_str());

if(p1->num!=0)
{
cout<<"请输入图书的价格"<<endl;
cin>>str;
while(!check(str))
{
cout<<"刚才输入的不是数字，请重新输入，按0返回！！！"<<endl;
cin>>str;
}
p1->price=atof(str.c_str());
}

else
{
delete p1;
p2=NULL;
p2->next=NULL;
head=NULL;
return head;
}

while(p1->num!=0)
{
p2=p1;
p1=new book;
cout<<"请输入图书的编号，以0结束"<<endl;
cin>>str;

while(!check(str))
{
cout<<"刚才输入的不是数字，请重新输入，按0返回！！！"<<endl;
cin>>str;
}

p1->num=atoi(str.c_str());

if(p1->num!=0)
{

cout<<"请输入图书的价格"<<endl;
cin>>str;

while(!check(str))
{
cout<<"刚才输入的不是数字，请重新输入，按0返回！！！"<<endl;
cin>>str;
}
p1->price=atof(str.c_str());
}
p2->next=p1;
}

delete p1;
p2->next=NULL;
return head;
}

void showbook(book *head)
{
cout<<endl;
cout<<"图书信息如下："<<endl;
while(head)
{
cout<<"图书编号："<<head->num<<"\t";
cout<<"价格："<<head->price<<endl;
head=head->next;
}
}

book* Delete(book *head,int num)
{
book *l,*p;
p=head;
if(head->num==num)
{
l=head;
head=head->next;
//::head=head;这句话没有达到你想要的效果，外面的head没有被修改啊！
printf("%d",head);
delete l;
cout<<"操作成功"<<endl;
return head;
}

while(p)
{
if(p->next==NULL)
{
cout<<"找不到要删除的编号。"<<endl;
return head;
}

if(p->next->num==num)
{
l=p->next;
p->next=l->next;
delete l;
cout<<"操作成功"<<endl;
return head;
}

p=p->next;
}
cout<<"找不到要删除的编号。"<<endl;
}

int main()
{
book *head=NULL;
head=creat();
showbook(head);
cout<<"请输入要删除的编号：";
int BookNum;
cin>>BookNum;
head=Delete(head,BookNum);
showbook(head);
return 0;
}

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