运行程序前，新建一个文本文件1.txt放在C盘下（或者修改下面的Read("c:\\1.txt", head);为你的文件名和路径）
文件内容：

1,aaa,82
2,bbb,99
3,ccc,75
4,ddd,63
5,eee,78
6,fff,60
7,test,92.5

以下是程序，用VS2010编译

// Q703974.cpp : Defines the entry point for the console application.
//

#include "stdafx.h"

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

typedef struct Student
{
    char no[10];
    char name[10];
    double score;
};

typedef struct Node
{
    Node * next;
    Student * s;
};

void Read(char * filename, Node * head)
{
    FILE * fp;
    fp = fopen(filename, "r");
    fseek(fp, 0, SEEK_END);
    long filesize = ftell(fp);
    rewind(fp);
    char * pBuff = (char *)malloc(sizeof(char) * filesize + 1);
    memset(pBuff, 0, filesize + 1);
    fread(pBuff, filesize, 1, fp);
    pBuff[filesize] = '\0';
    int offset = 0;
    while (true)
    {
        Student * pstu = (Student *)malloc(sizeof(Student));
        int n = sscanf(pBuff + offset, "%[^,],%[^,],%lf", pstu->no, pstu->name, &pstu->score);
        if (n != 3) break;


        Node * curr = head;
        while (true)
        {
            if (curr->next == NULL) 
            {
                head->next = (Node *)malloc(sizeof(Node));
                head->next->next = NULL;
                head->next->s = pstu;
                break;
            }
            else if (curr->next->s->score > pstu->score)
            {
                Node * t = (Node *)malloc(sizeof(Node));
                t->next = curr->next;
                t->s = pstu;
                curr->next = t;
                break;
            }
            curr = curr->next;
        }

        while (pBuff[offset] != '\n' && pBuff[offset] != '\0') 
            offset++;
        if (pBuff[offset - 1] == '\0') break; else offset++;
    }
    free(pBuff);
    fclose(fp);
}

int _tmain(int argc, _TCHAR* argv[])
{
    Node * head = (Node *)malloc(sizeof(Node));
    head->next = NULL;
    Read("c:\\1.txt", head);
    while (head->next != NULL)
    {
        printf("%s\t%s\t%lf\n", head->next->s->no, head->next->s->name, head->next->s->score);
        head = head->next;
    }
    return 0;
}

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之前看错了题目，一个小问题，是学号排序，不是成绩，只要改1行：
else if (curr->next->s->score > pstu->score)
修改为
lse if (strcmp(curr->next->s->no, pstu->no) > 0)

输入：
13 Bob 85
6 Tim 73
9 Jim 60
输出：
6 Tim 73
9 Jim 60
13 Bob 85

文件流我这里不方便操作，自己修改一下就行了，这里以输入3个学生为例

 #include<stdio.h>
#include<malloc.h>
typedef struct student {
    int id;             //学号
    char name[20];      //姓名
    int mark;           //成绩
};
typedef struct Node {
    student t;
    Node* next;
}*Linklist;
void initlist(Linklist list, int n) {
    Node *p, *r;
    r = list;
    for (int i = 0; i < n; i++) {
        p = (Linklist)malloc(sizeof(Node));
        scanf("%d%s%d", &p->t.id, &p->t.name, &p->t.mark);   //按顺序输入学号、姓名、成绩
        p->next = NULL;
        r->next = p;
        r = p;
    }
}
void sortlist(Linklist list) {      //冒泡排序
    student tmp;
    for (Node *i = list->next; i!= NULL; i = i->next) {
        for (Node *j = i->next; j != NULL; j = j->next) {
            if (i->t.id > j->t.id) {
                tmp = i->t;
                i->t = j->t;
                j->t = tmp;
            }
        }
    }
}
void showlist(Linklist list) {
    Node *p = list->next;
    printf("\n");
    while (p != NULL) {
        printf("%d %s %d\n", p->t.id, p->t.name, p->t.mark);
        p = p->next;
    }
}
int main() {
    Linklist list;
    list = (Linklist)malloc(sizeof(Node));
    int n = 3;
    initlist(list,3); //输入3组数据
    sortlist(list);
    showlist(list);
    return 0;
}