void save()
    {
        FILE *fp;
        int i;
        if((fp=fopen("stu_infer","wb"))==NULL)
        {
            printf("\n\n\t\t\t文件打开失败!!!");
            return;
        }
        for(i=0;i<max+1;i++)
            if(fwrite(&stu[i],sizeof(struct student),1,fp)!=1)
                printf("\n\n\t\t\t文件保存错误!!!");
            fclose(fp);
    }