#include "stdafx.h"
#include "stdio.h"
#include "string.h"
#include "conio.h"
struct student
{
    long num;
    float score;
    struct student *next;
};
struct student *del(struct student *head1,struct student *head2)
{
    struct student *p1,*p2,*p3;
    for(p2=head2;p2!=NULL;p2=p2->next)
    {
        for(p1=head1;p1!=NULL;p3=p1,p1=p1->next)
        {
            if(p1->num==p2->num)               
            {
                if(p1==head1) head1=p1->next;   
                else p3->next=p1->next;         
            }
        }
    }
    return(head1);
}
struct student *del1(struct student *head1,struct student *head2)//我要查找两个链表的相同元素，然后将相同的元素删除？第一个链表能够删除，第二个链表不能删除，代码该如何编写？
{
    struct student *p1,*p2,*p3;
    for(p2=head2;p2!=NULL;p2=p2->next)
    {
        for(p1=head1;p1!=NULL;p3=p1,p1=p1->next)
        {
            if(p2->num=p1->num)
            {
                if(p2==head2)
                    head2=p2->next;
                else
                    p2=p2->next;
            }
        }
        return (head2);
    }
}
int main(int argc, char* argv[])
{
    struct student a,b,c,d,e,f,*head1,*head2,*p,*q,*w;
    a.num=99101;a.score=89;
    b.num=99102;b.score=90;
    c.num=99103;c.score=91;
    head1=&a;
    a.next=&b;
    b.next=&c;
    c.next=NULL;
    p=head1;
    printf("Linklist 1:\n");
    while(p!=NULL)
    {
        printf("%ld%5.1f\n",p->num,p->score);
        p=p->next;
    }
    printf("\n");
    d.num=99103;d.score=92;
    e.num=99104;e.score=93;
    f.num=99105;f.score=94;
    head2=&d;
    d.next=&e;
    e.next=&f;
    f.next=NULL;
    q=head2;
    printf("Linklist:\n");
    while(q!=NULL)
    {
        printf("%ld%5.1f\n",q->num,q->score);
        q=q->next;
    }
    printf("\n");
    head1=del(head1,head2);
    printf("delete Linklist 1:\n");
    for(p=head1;p!=NULL;p=p->next)
    {
       printf("%ld%5.1f\n",p->num,p->score);
      
    }
    printf("\n");
    head2=del(head1,head2);
    printf("delete Linklist 2:\n");
    for(q=head2;q!=NULL;q=q->next)
    {
        printf("%ld%5.1f\n",q->num,q->score);
    }
    return 0;
}

看了一下，你写了一个删除链表一的函数，和一个删链表二的函数，
你调用删除链表一的函数后，链表一已把跟链表二相同的删去，到再调用链表二时，肯定找不到相同的数了，所以会出现你说的链表二删不去。
其实，这两函数可以合为一个函数，只要一个函数就可以同时删去链表一和链表二相同的数。

那该怎么样合并啊？

用到指针的指针。
你的我改了一下，你看看，

#include "stdio.h"
#include "string.h"
#include "conio.h"
struct student
{
    long num;
    float score;
    struct student *next;
};
del(struct student **head3,struct student **head4)
{
    struct student *head1,*head2,*p1,*p2,*p3,*p4;
    head1=*head3;
    head2=*head4;
    p3=head2;
    p4=head1;
    for(p2=head2;p2!=NULL;)
    {
    for(p1=head1;p1!=NULL;)
        {
            if(p1->num==p2->num)
        {
          if(p2==head2)
        {
         p3=p3->next;
         head2=p3;
         p2=p3;
        }
          else
        p3->next=p2->next;

          if(p1==head1)
        {
         p4=p4->next;
         head1=p4;
         p1=p4;
        }
          else
        p4->next=p1->next;
        }
      p4=p1;
      p1=p1->next;
    }
       p3=p2;
       p2=p2->next;
    }
  *head3=head1;
  *head4=head2;
}





int main(int argc, char* argv[])
{
    struct student a,b,c,d,e,f,*head1,*head2,*p,*q,*w;
    a.num=99101;a.score=89;
    b.num=99102;b.score=90;
    c.num=99103;c.score=91;
    head1=&a;
    a.next=&b;
    b.next=&c;
    c.next=NULL;
    p=head1;
    printf("Linklist 1:\n");
    while(p!=NULL)
    {
        printf("%ld%5.1f\n",p->num,p->score);
        p=p->next;
    }
    printf("\n");
    d.num=99103;d.score=92;
    e.num=99104;e.score=93;
    f.num=99105;f.score=94;
    head2=&d;
    d.next=&e;
    e.next=&f;
    f.next=NULL;
    q=head2;
    printf("Linklist:\n");
    while(q!=NULL)
    {
        printf("%ld%5.1f\n",q->num,q->score);
        q=q->next;
    }
    printf("\n");
    del(&head1,&head2);
    printf("delete Linklist 1:\n");
    for(p=head1;p!=NULL;p=p->next)
    {
       printf("%ld%5.1f\n",p->num,p->score);

    }
    printf("\n");
    printf("delete Linklist 2:\n");
    for(q=head2;q!=NULL;q=q->next)
    {
        printf("%ld%5.1f\n",q->num,q->score);
    }
    return 0;
}


还有没有其他的做法啊？

我写的代码还是有错误，帮我修改一下，链表二还是不能删除
#include "stdafx.h"
#include "stdio.h"
#include "string.h"
#define NULL 0
struct student
{
    long num;
    float score;
    struct student *next;
};

struct student *del(struct student *head1,struct student *head2)
{
    struct student *p1,*p2,*p3;
    for(p2=head2;p2!=NULL;p2=p2->next)
    {
        for(p1=head1;p1!=NULL;p3=p1,p1=p1->next)
        {
            if(p1->num==p2->num)               
            {
                if(p1==head1)
                    head1=p1->next;     
                else
                    p3->next=p1->next;  
             }
        }
    }
    return(head1);
}

struct student *del1(struct student *head1,struct student *head2)
{
    struct student *p1,*p2,*p3,*p4;
    for(p2=head2;p2!=NULL;p2=p2->next)
    {
        for(p1=head1;p1!=NULL;p3=p1,p1=p1->next)
        {
            if(p1->num==p2->num)
            {
                if(p2==head2)
                    head2=p2->next;
                else
                    p4->next=p2->next;
            }
        }
      
    }
     return(head2);
}

int _tmain(int argc, _TCHAR* argv[])
{
    struct student a,b,c,d,e,f,*head1,*head2,*p,*q,*w;
    a.num=99101;a.score=89.5;
    b.num=99102;b.score=90.5;
    c.num=99103;c.score=91.5;
   
    head1=&a;
    a.next=&b;
    b.next=&c;
    c.next=NULL;
    p=head1;
    printf("Linklist 1:\n");
    while(p!=NULL)
    {
        printf("%ld%5.1f\n",p->num,p->score);
        p=p->next;
    }
    printf("\n");
   
    d.num=99103;d.score=92.5;
    e.num=99104;e.score=93.5;
    f.num=99105;f.score=94.5;
   
    head2=&d;
    d.next=&e;
    e.next=&f;
    f.next=NULL;
    q=head2;
    printf("Linklist:\n");
    while(q!=NULL)
    {
        printf("%ld%5.1f\n",q->num,q->score);
        q=q->next;
    }
   
    printf("\n");
    head1=del(head1,head2);
    printf("delete Linklist 1:\n");
    for(p=head1;p!=NULL;p=p->next)
    {
       printf("%ld%5.1f\n",p->num,p->score);
      
    }
    head2=del1(head1,head2);
    printf("delete Linklist 2:\n");
    for(q=head2;q!=NULL;q=q->next)
    {
        printf("%ld%5.1f\n",q->num,q->score);
    }
    return 0;
}

你用TC试我的代码吧，TC和VC编译会有不一样，但算法是可行的。

只能用二级指针吗？

是不是第二个del1()函数的循环有问题还是什么啊？