#include <stdio.h>
#include <string.h>
class student
{
    char name[30];
    float math;
    float chinese;
    float english;
    float average;
}one[100];
int MenuChoice(int);
int EnterAccount(int);
void Enter( student *fst);
void Amend( student *src);
void Delete( student *next);
void print( student *out);

main()
{
   
    student one[100]={0},*look=one;
    int menu,t;

    while((menu=MenuChioce())!=0)
        if(menu>1 && menu<=4 && (t=EnterAccount()))
        {
            look=one+t;
            switch(menu)
            {
            case 1:
                Enter(look);
                break;
            case 2:
                if (strcmp(look->name,""))
                printf("学号:%d\n姓名: %s\n语文成绩: %f\n数学成绩:%f\n英语成绩: %f\n平均成绩:%f\n",t, look->name, look->chinese, look->math, look->english, look->average);
                else
                  printf("对不起,该学号不存在!\n");
                break;
            case 3:
                Amend(look);
                break;
            case 4:
                Delete(look);
                break;
            }
        }
else if(menu==5)
print(one);
else
printf("错误的请求!\n");

return 0;
}

int MenuChioce(int)
{
    int choice;
    printf("请选择:\n"
  "1 - 新建学生信息\n"
  "2 - 查找学生信息\n"
  "3 - 修改学生信息\n"
  "4 - 删除学生信息\n"
  "5 - 打印学生信息\n"
  "0 - 退出\n");
    scanf("%d",&choice);
    return choice;
}

int EnterAccount(int)
{
    int ret;
    printf("请输入学号:\n");
    scanf("%d",&ret);

    if(ret>=1 && ret<=100)
        return ret-1;
return 0;
}

void Enter(struct student *fst)
{
    printf("请输入学生姓名、语文成绩、数学成绩、英语成绩和平均成绩\n");
    scanf("%s%f%f%f",*fst->name,&fst->chinese,&fst->math,&fst->english,&fst->average);

}

void Amend(struct student &src)
{
    int t;
    printf("请选择:\n"
  "1 - 修改学生姓名\n"
  "2 - 修改学生语文成绩\n"
  "3 - 修改学生数学成绩\n"
  "4 - 修改学生英语成绩\n"
  "5 - 修改学生平均成绩\n");
    scanf("%d",&t);

    switch(t)
    {
    case 1:
        printf("请输入学生的新名字\n");
        scanf("%s",&src->name);
        break;
    case 2:
        printf("请输入学生新的语文成绩");
        scanf("%f",&src->chinese);
        break;
    case 3:
        printf("请输入学生新的数学成绩\n");
        scanf("%f",&src->math);
        break;
    case 4:
        printf("请输入学生新的英语成绩\n");
        scanf("%f",&src->english);
        break;
    case 5:
        printf("请输入学生新的平均成绩\n");
        scanf("%f",&src->average);
        break;
    }
}

void Delete(struct student *next)
{
    strcpy(next->name,"");
    next->math = next->english = next->chinese = next->average = 0.0;

}

void print(struct student *out)
{
    struct student *up;

    for(up = out;out < &up[100]; out++)
        if(strcmp(out->name,""))
            printf("学号:%d\n姓名: %s\n语文成绩: %f\n数学成绩:%f\n英语成绩: %f\n平均成绩:%f\n",
             out-up + 1,out->name,out->chinese,out->math;out->english,  out->average);


}

到底你想修改什么啊?

改正确就行啊

我觉得应该是这个CLASS不能识别[]操作符!