合并链表，按主键升序

已有两个链表，每个链表中的结点包括学号，成绩。要求把两个链表合并，按学号升序排列。

#define _CRT_SECURE_NO_WARNINGS
#include <stdio.h>  
#include <stdlib.h>  
#define N 10  

typedef struct student
{
    int num;
    float score;
    struct student *next;
}stu;

stu *creat()
{
    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 print(stu *p)
{
    while (p != NULL)
    {
        printf("%d	%.2f
", p->num, p->score);
        p = p->next;
    }
}

stu *link(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;
}

int main()
{
    stu *a, *b, *c;
    printf("
请输入链表a的信息，学号小于等于零时结束输入：格式(学号,成绩)
");
    a = creat();
    printf("
请输入链表b的信息，学号小于等于零时结束输入：格式(学号 成绩)
");
    b = creat();
    printf("
链表a的信息为：
");
    print(a);
    printf("
链表b的信息为：
");
    print(b);
    c = link(a, b);
    printf("
合并后的链表信息为：
");
    print(c);
    return 0;
}