两个链表按升序合并

设已经建立两个链表，且两个链表都是以学号升序排列写的，要求编写一个函数，将两个链表按升序合并。

#include < stdlib.h >
#include < stdio.h >
#include < conio.h >
#include < ctype.h >

#define  LEN sizeof(struct student)

extern  unsigned _floatconvert;     /* 防止floating point formats not linked 错误发生 */
#pragma extref _floatconvert

typedef  struct  student    
{
     long  num;
     float  score;
     struct  student  * next;
}STU;

STU  * CreateEnd()
{
     int  n = 0 ;
    STU  * p1, * p2, * head;
    head = NULL;
    p1 = (STU  * )malloc(LEN);         /* 创建第一个结点 */
    scanf( " %ld,%f " , & p1 -> num, & p1 -> score);
    p1 -> next = NULL;
     while (p1 -> num != 0 )         /* 将结点加入链表 */
    {
         ++ n;
         if (n == 1 )         /* 是第一个结点，作表头 */
            head = p1;
         else              /* 不是第一个结点，作表尾 */
            p2 -> next = p1;
        p2 = p1;
        p1 = (STU  * )malloc(LEN);     /* 开辟下一个结点 */
        scanf( " %ld,%f " , & p1 -> num, & p1 -> score);
        p1 -> next = NULL;
    }
    free(p1);             /* 释放最后一个结点所占的内存 */
     return  (head);             /* 返回链表的头指针 */
}

void  print(STU  * head)
{
    STU  * p;
    p = head;
     do
    {
        printf( " %ld\t%5.1f\n " ,p -> num,p -> score);
        p = p -> next;
    } while (p != NULL);
}

STU  * merge(STU  * p1,STU  * p2)
{
    STU  * p, * head;
     if (p1 -> num < p2 -> num)
    {
        head = p = p1;p1 = p1 -> next;}
     else
    {
        head = p = p2;p2 = p2 -> next;}
     while (p1 != NULL  &&  p2 != NULL)
         if (p1 -> num < p2 -> num)
        {
            p -> next = p1;
            p = p1;
            p1 = p1 -> next;
        }
         else
        {
            p -> next = p2;
            p = p2;
            p2 = p2 -> next;
        }
     if (p1 != NULL)
        p -> next = p1;
     else
        p -> next = p2;
     return  head;
}

void  main()
{
    STU  * p1, * p2, * head;
    printf( " Please input first link information:\n " );
    p1 = CreateEnd();
    print(p1);
    printf( " \nPlease input second link information:\n " );
    p2 = CreateEnd();
    print(p2);
    printf( " \nThe merged link is:\n " );
    head = merge(p1,p2);
    print(head);
    getch();
}