使用c语言，设计一个简单的学生成绩管理系统。设有学生成绩文件student.txt，每位学生成绩信息包含学号（num）、姓名（name）、性别（sex）、出生日期（birthday，包括年、月、日，分别表示为year,month,day）、3门功课的成绩（高数、C语言、大学物理）、总分和平均分。设计程序，要求从文件student.txt中读出学生成绩表，之后参对成绩表进行如下操作 添加。可添加一条或多条记录。

好的，我已经回答过这个问题了，您可以参考上面的回答。这里再给您提供一下完整的代码，包括添加多条记录的功能：

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

struct student {
    int num;
    char name[20];
    char sex[10];
    int year, month, day;
    float math, c_language, physics, total, average;
}stu[100];

int main() {
    FILE *fp;
    int i, n, m;
    char ch;
    fp = fopen("student.txt", "r");
    if(fp == NULL) {
        printf("File does not exist!\n");
        exit(1);
    }
    n = 0;
    while(!feof(fp)) {
        fscanf(fp, "%d %s %s %d %d %d %f %f %f %f %f", &stu[n].num, stu[n].name, stu[n].sex, &stu[n].year, &stu[n].month, &stu[n].day, &stu[n].math, &stu[n].c_language, &stu[n].physics, &stu[n].total, &stu[n].average);
        n++;
    }
    fclose(fp);
    printf("The original student score information is as follows:\n");
    printf("num    name    sex    birthday    math    c_language    physics    total    average\n");
    for(i = 0; i < n; i++) {
        printf("%d    %s    %s    %d/%d/%d    %.2f    %.2f    %.2f    %.2f    %.2f\n", stu[i].num, stu[i].name, stu[i].sex, stu[i].year, stu[i].month, stu[i].day, stu[i].math, stu[i].c_language, stu[i].physics, stu[i].total, stu[i].average);
    }
    printf("Do you want to add a new student score information? (y/n)\n");
    scanf(" %c", &ch);
    while(ch == 'y' || ch == 'Y') {
        printf("Please enter the number of student score information you want to add:\n");
        scanf("%d", &m);
        printf("Please enter the new student score information:\n");
        for(i = n; i < n + m; i++) {
            printf("num: ");
            scanf("%d", &stu[i].num);
            printf("name: ");
            scanf("%s", stu[i].name);
            printf("sex: ");
            scanf("%s", stu[i].sex);
            printf("birthday(year, month, day): ");
            scanf("%d %d %d", &stu[i].year, &stu[i].month, &stu[i].day);
            printf("math: ");
            scanf("%f", &stu[i].math);
            printf("c_language: ");
            scanf("%f", &stu[i].c_language);
            printf("physics: ");
            scanf("%f", &stu[i].physics);
            stu[i].total = stu[i].math + stu[i].c_language + stu[i].physics;
            stu[i].average = stu[i].total / 3;
        }
        n += m;
        fp = fopen("student.txt", "a");
        if(fp == NULL) {
            printf("File open failed!\n");
            exit(1);
        }
        for(i = n - m; i < n; i++) {
            fprintf(fp, "%d %s %s %d %d %d %.2f %.2f %.2f %.2f %.2f\n", stu[i].num, stu[i].name, stu[i].sex, stu[i].year, stu[i].month, stu[i].day, stu[i].math, stu[i].c_language, stu[i].physics, stu[i].total, stu[i].average);
        }
        fclose(fp);
        printf("The new student score information has been added successfully!\n");
        printf("Do you want to add more student score information? (y/n)\n");
        scanf(" %c", &ch);
    }
    if(ch == 'n' || ch == 'N') {
        printf("No new student score information is added!\n");
    }
    return 0;
}

当您运行该程序时，它会先读取文件student.txt中的学生成绩信息，并将其输出到屏幕上。然后，它会询问您是否要添加新的学生成绩信息。如果您选择“y”或“Y”，则会提示您输入要添加的学生人数，然后提示您逐一输入每一位学生的信息。最后，程序会将新的学生成绩信息添加到文件student.txt中，并输出提示信息。如果您选择“n”或“N”，则程序不会添加新的学生成绩信息。