这个是我编写的一个链表的一部分。就是在查找和修改这里出了问题/但是我不知道哪里错了呀/也有可能
是main函数里面调用错了的。请各位高手帮我看看/并且给我修改下；谢谢各位了



//链表的查找
struct lesson *find(struct lesson *head,long num)
{
    struct lesson*p1,*p2;
    if(head==NULL)
    {
        cout<<"这是一个空的课程表!"<<endl;
        goto end;
    }    
    p1=head;
    while(num!=p1->num&&p1->next!=NULL)
    {
        p2=p1;
        p1=p1->next;
    }
    if(num==p1->num)
        cout<<"你找到的科目是:"<<num<<endl;
    else
        cout<<"没有你要找的科目"<<endl;
          end:
    return (head);
}
//链表的修改
struct lesson *set(struct lesson *head,long num,struct lesson *l)
{
    struct lesson *p1,*p2,*p3;
    p3=l;
    if(head==NULL)
    {
        cout<<"这是一个空的课程表!"<<endl;
        goto end;
    }
    p1=head;
    while(num!=p1->num&&p1->next!=NULL)
    {
        p2=p1;
        p1=p1->next;
    }
    if(num==p1->num)
    {
       cout<<"请输入要修改的课程的编号和名字："<<endl;
       cin>>p3->num>>p3->name;
       p3->next=p1;
       p2->next=p3;

    }
    else
        cout<<"没有你想要修改的课程!"<<endl;
        end:
    return (head);
}
//课程的统计(没编好)
int main()
{
    struct lesson *head,les;
    long delnum;long fnum;long snum;
    cout<<"请输入数据："<<endl;
    head=creat();//返回头指针
    print(head);
    cout<<"请输入要添加的科目："<<endl;
    cin>>les.num>>les.name;
    head=insert(head,&les);
    print(head);
    cout<<"请输入要删除的科目："<<endl;
    cin>>delnum;
    head=del(head,delnum);//删除后链表的头地址
    print(head);
    cout<<"请输入要查找的科目："<<endl;
    head=find(head,fnum);
    print(head);
    cout<<"请输入你要修改的科目："<<endl;
    head=set(head,snum,&les);
    print(head);
    return 0;
}