有两个链表a和b，设结点中包含学号、姓名。从a链表中删去与b链表中有相同学号的那些结点。

#include  < stdio.h >
#include  < stdlib.h >
#define  N 10
typedef  struct  student
{
     int  num;
     float  score;
     struct  student  * next;
}STU;

STU  * create()
{
     int  i;
    STU  * p, * head = NULL, * tail = head;
     for  (i = 0 ;i < N;i ++ )
    {
        p = (STU  * )malloc( sizeof (STU));
        scanf( " %d%f " , & p -> num, & p -> score);
        p -> next = NULL;
         if  (p -> num < 0 )
        {
            free(p);
             break ;
        }
         if (head == NULL)
            head = p;
         else
            tail -> next = p;
        tail = p;
    }
     return  head;
}

void  output(STU  * p)
{
     while  (p != NULL)
    {
        printf( " %d\t%.2f\n " ,p -> num,p -> score);
        p = p -> next;
    }
}

STU  * del(STU  * a,STU  * b)
{
    STU  * head, * p1, * p2;
    p1 = p2 = head = a;                         // 让p1、p2、head结点指向链表a的头部
     while  (b != NULL)
    {
        p1 = p2 = head;                         // 每次循环前让p1、p2始终指向删除后链表的头部
         while  (p1 != NULL)
        {    
             if  (b -> num == p1 -> num)         // 学号相同，删除结点信息
                 if (p1 == head)             // 如果删除的是头结点，则头结点位置要后移
                {
                    head = p1 -> next;
                    free(p1);
                    p1 = p2 = head;
                }
                 else                      // 如果删除的是中间结点
                {
                    p2 -> next = p1 -> next;
                    free(p1);
                    p1 = p2 -> next;
                }
             else                          // 学号不同，则p1,p2指针依次后移
            {
                p2 = p1;
                p1 = p1 -> next;
            }
        }
        b = b -> next;
    }
     return  head;
}

int  main( int  argc,  char   * argv[]) 
{
    STU  * a, * b, * c;
    printf( " \n请输入链表a的信息，学号小于零时结束输入：格式(学号 成绩)\n " );
    a = create();
    printf( " \n请输入链表b的信息，学号小于零时结束输入：格式(学号 成绩)\n " );
    b = create();
    system( " cls " );
    printf( " \n链表a的信息为：\n " );
    output(a);
    printf( " \n链表b的信息为：\n " );
    output(b);
    c = del(a,b);
    printf( " \n删除后的链表信息为：\n " );
    output(c);

     return   0 ;
}