#include "stdio.h"
#include "stdlib.h"

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

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=99107;b.score=90;
    c.num=99103;c.score=91;
    head1=&a;
    a.next=&b;
    b.next=&c;
    c.next=NULL;
    p=head1;
    printf("第一个链表为:\n");
    while(p!=NULL)
    {
        printf("%ld%5.1f\n",p->num,p->score);
        p=p->next;
    }
    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("第二个链表为：\n");
    while(q!=NULL)
    {
        printf("%ld%5.1f\n",q->num,q->score);
        q=q->next;
    }//如何将第一个链表和第二个链表合并，并按num升序排序？
    return 0;
}

你去查查 merge sort 相关的内容，看看能不能解决你的问题。

#include "stdio.h"
#include "stdlib.h"

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

struct student *q_sort(struct student *head1,struct student *head2)
{
 struct student *p1=head1,*p2,*px;
 struct student pm;
 for(;p1->next!=NULL;)
    p1=p1->next;
 p1->next=head2;
 for(p1=head1;p1->next!=NULL;p1=p1->next)
    for(p2=p1->next;p2!=NULL;p2=p2->next)
       if(p1->num>p2->num)
         {
          pm=*p1;*p1=*p2;*p2=pm;
          px=p1->next;p1->next=p2->next;p2->next=px;
         }
 return head1;
}

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=99107;b.score=90;
    c.num=99103;c.score=91;
    head1=&a;
    a.next=&b;
    b.next=&c;
    c.next=NULL;
    p=head1;
    printf("第一个链表为:\n");
    while(p!=NULL)
    {
        printf("%ld%5.1f\n",p->num,p->score);
        p=p->next;
    }
    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("第二个链表为：\n");
    while(q!=NULL)
    {
        printf("%ld%5.1f\n",q->num,q->score);
        q=q->next;
    }//如何将第一个链表和第二个链表合并，并按num升序排序？
   
    head1=q_sort(head1,head2);
    printf("合并并排序后的链表为：\n");
    p=head1;
    while(p!=NULL)
    {
        printf("%ld%5.1f\n",p->num,p->score);
        p=p->next;
     }
    system("pause");
    return 0;
}

看下数据结构链表的那章！