新手，实在解决不了问题了，只能求助别人了。问题是要写一个歌手大赛系统，code我已经写了，但有错误，看了好久，我也看不出要怎么解决问题，无奈新手太渣，求帮助解决问题，先谢谢了。。。
下面是题目：
对一次歌手比赛的成绩进行管理，功能要求：1、输入每个选手的数据包括编号、姓名、十个评委的成绩，根据输入计算出总成绩和平均成绩（去掉最高分，去掉最低分）。2、显示主菜单如下：1）输入选手数据 2）评委打分 3）成绩排序（按平均分）4）数据查询  5）追加学生数据 6）写入数据文件7）退出系统。
下面是code:
#include<stdio.h>
#include<stdlib.h>
#include<string.h>
#include<time.h>
#define M 10      
#define N  5      
int add=N-1;
int sum[N]={0},Max[N],Min[N];
float aver[N]={0};
struct Singer_I     
{
    int num;
    char name[8];
    int score[M];
};




void Input_Singer(struct Singer_I a[],int n)
{
    int i;
    for(i=0;i<n;i++)
        scanf("%d %s",&a[i].num,&a[i].name);
}


 void Input_Score(int score[],int n)
{
    int i;
    for(i=0;i<n;i++)
        score[i]=1+(int)10*rand()/(RAND_MAX+1);
    return 0;
}


void sort(struct Singer_I a[],float b[],int n)
{
    int i,j,k,t;
    float temp;
    char str[8];
    for(i=0;i<n;i++)
    {
        k=i;
        for(j=i+1;j<n;j++)
            if(b[k]>b[j])
                k=j;
            if(k!=i)
            {
                temp=b[i];
                b[i]=b[k];
                b[k]=temp;

                strcpy(str,a[i].name);
                strcpy(a[i].name,a[k].name);
                strcpy(a[k].name,str);

                t=a[i].num;
                a[i].num=a[k].num;
                a[k].num=t;
            }

    }
}




void main()
{
   
    FILE *fp;
    fp=fopen("smsty1.text","w+");
    struct Singer_I a[20];
    void Input_Singer(struct Singer_I a[],int n);
        void Input_Score(int score[],int n);
        void sort(struct Singer_I a[],float b[],int n);
    printf("******************1.输入选手数据****************\n");
    printf("******************2.评  委 打 分****************\n");
    printf("******************3.成  绩 排 序****************\n");
    printf("******************4.数  据 查 询****************\n");
    printf("******************5.追加学生数据****************\n");
    printf("******************6.写入数据文件****************\n");
    printf("******************7.退  出 系 统****************\n");

    int flag=1;
    int i,j,n,m;
    while(flag)
    {
        printf("请输入操作指令:\n");
        scanf("%d",&n);
        switch(n)
        {
                 case 1:Input_Singer(a,N);                                       
                         break;                                                     
                 case 2:srand((unsigned)time(NULL));                             
                     for(i=0;i<N;i++)
                     {
                         printf("%d位选手的成绩:",i++);
                         Input_Score(a[i].score,M);                           
                    
                         for(j=0;j<M;j++)
                         printf("%d",a[i].score[j]);
                         printf("\n");
                     }
                         break;
                 case 3:for(i=0;i<N;i++)                           
                        {
                            Max[i]=a[i].score[0];
                            Min[i]=a[i].score[0];
                            for(j=0;j<M;j++)
                            {
                                sum[i]+=a[i].score[j];              
                                if(Max[i]<a[i].score[j])               
                                    Max[i]=a[i].score[j];
                                if(Min[i]>a[i].score[j])
                                    Min[i]=a[i].score[j];
                            }
                            aver[i]=(sum[i]-Min[i]-Max[i])/(M-2);      
                        }
                            sort(a,aver,N);                           
                            for(i=0;i<N;i++)
                                printf("%s,总分:%d,平均分:%5.2f",a[i].name,sum[i],aver[i]);
                            break;

                 case 4:printf("你要查询选手的数据:\n");                                   
                        scanf("%d",&m);
                        for(i=0;i<N;i++)
                            if(a[i].num==m)
                            {
                                printf("%d号,选手%s,总分:%d,最高分:%d,最低分:%d,平均分:%5.2f",a[i].num,a[i].name,sum[i],Max[i],Min[i],aver[i]);
                                printf("\n");
                            }
                            break;
                 case 5:printf("请输入要追加的选手的数据:\n");                    
                        add+=1;
                        scanf("%d %s",&a[add].num,&a[add].name);
                        break;
                 case 6:printf("写入数据文件中:\n");                              
                        for(i=0;i<add+1;i++)
                        {
                            fprintf(fp,"%d",a[i].num);         
                            fprintf(fp,"%s",a[i].name);
                            fprintf(fp,"%d\n",a[i].score);
                        }
                        break;
                 case 7:exit(0);                                                
                        break;                                   
                 default:flag=0;
        }
    }
}