c语言问题13

这个好像是谭浩强书上的题目他给出的答案有点问题。正好我写过了，贴出来。
/* 删除a链表中和b链表相同的学号对应的结点 */
#define LA 7
#define LB 5
#define NULL 0
#include "string.h"
#include "stdlib.h"
#include "stdio.h"
#include "conio.h"
struct student
{ char num[6];
char name[8];
struct student *next;
} a[LA],b[LB];
void main(void)
{
struct student a[LA]={{"101","Wang"},{"102","Zhang"},{"103","Wei"},{"106","Gao"},{"108","Cao"},{"109","Dong"},{"111","Zhen"}};
struct student b[LB]={{"102","Zhang"},{"103","Wei"},{"105","Chen"},{"106","Gao"},{"111","Zhen"}};
int i,j,flag;
struct student *p,*p1,*p2,*pt,*head1,*head2;
head1=a;
head2=b;
printf