链表相减

书上题目，要用带头链表处理

#include <iostream>
#include <cstdio>
#include <cstdlib>
using namespace std;
typedef struct node
{
    int date;
    struct node *next;
}listnode,*linklist;
linklist initlist(linklist head)    /*链表初始化*/
{
    head=new node;    /*申请内存*/
    if(head==NULL)
        cout<<"链表创建失败";
    else
        head->next=NULL;
    return head;
}
int listempty(linklist head)
{
    if(head->next==NULL)
        return 1;
    return 0;
}
int inputlist(linklist head,int n)
{
    int i,t;
    linklist tail=NULL,temp=NULL;
    for(i=0;i<n;i++)
    {
        if(tail==NULL)    //开始出错了
        {
            tail=head;
            cin>>t;
            head->date=t;
        }
        else
        {
            temp=new node;
            cin>>t;
            temp->date=t;
            tail->next=temp;
            tail=temp;
            tail->next=NULL;
        }
    }
    return 0;
}
void outputlist(linklist head)
{
    linklist p=head;
    while(p!=NULL)
    {
        cout<<p->date<<' ';
        p=p->next;
    }
    cout<<endl;
}
void destroylinklist(linklist head)
{
    linklist p=head,q=NULL;
    while(p!=NULL)
    {
        q=p;
        p=p->next;
        free(q);
    }
}
void insert(linklist head,int n,int num)
{
    linklist p=head,q=head,temp,l;
    int i;
    for(i=0;i<n;i++)
    {
        q=p;
        p=p->next;
    }
    temp=p;
    l=new listnode;
    l->date=num;
    l->next=temp;
    q->next=l;
}
int listlen(linklist head)
{
    int count=0;
    linklist p=head;
    while(p!=NULL)
    {
        count++;
        p=p->next;
    }
    return count;
}
linklist del(linklist head1,linklist head2)
{
    int i,flag=0;
    linklist H1,q=head2;
    H1=new listnode;
        H1->next=head1;
    linklist pre=H1,p=H1->next;
    while(p!=NULL)
    {
        flag=0;
        q=head2;
        while(q!=NULL)
        {
            if(p->date==q->date)
            {
                pre->next=p->next;
                flag=1;
            }
            q=q->next;
        }
        if(flag==0)
        {
            pre=p;
            p=p->next;
        }
        else
        {
            p=pre->next;
        }
    }
    return H1->next;
}
int main()
{
    linklist head1,head2;
    head1=initlist(head1);
    head2=initlist(head2);
    inputlist(head1,6);
    inputlist(head2,5);
    head1=del(head1,head2);
    outputlist(head1);
    return 0;      
}