#include<stdio.h>
#include<stdlib.h>
#define M 1000

struct subjects
{
    float *Math;
    float *English;
    float *Chinese;
};
struct stu
{
    char *name;//名字
    long *num;//学号
    struct subjects score;//输入成绩
}stu[M],*p;

int main()
{
    FILE* fp;
    int i,choose,n=0;
    if ((fopen_s(&fp,"list.txt", "wb+"))!=0)
    {
        printf("can't  creat  file! return...\n");
        exit(0);
    }
    for (i = 0; i < M; i++)
    {
        
        printf("输入名字:");
        scanf_s("%s", &p->name);
        printf("输入学号:");
        scanf_s("%d", &p->num);
        printf("输入成绩:\n");
        printf("   数学:");
        scanf_s("%f", &p->score.Math);
        printf("   英语:");
        scanf_s("%f", &p->score.English);
        printf("   语文:");
        scanf_s("%f", &p->score.Chinese);
        n = i;
        printf("按任意键继续，若输入完成按0退出\n");
        scanf_s("%d", &choose);
        if (choose == 0)
            exit(0);
        
    }
    for (i = 0; i < n; i++, p++)
    {
        fprintf_s(fp, "%2s%2d%2f%2f%2f", p->name, p->num, p->score.Math, p->score.English, p->score.Chinese);
        printf("\n");
    }
    fclose(fp);
    return 0;
}

这个函数fopen_s你有写过吗？
还有，有专门的打开文件函数fopen唉。