#include <stdio.h>
#define N 5
struct student
{
    char id[10];
    char name[10];
    int sub[4];
    float ave;
    int total;
   
}stu[N],a;
struct student grade;

main()
{
    FILE *f1;
    int i,j;
    float ave[4];

    printf("Please input the information of the 5 students and their grades \n");
    for(i=0;i<N;i++){
        stu[i].total = 0;
        printf("NO.%d：",i+1);
        scanf("%s %s",stu[i].id,stu[i].name);
        for(j=0;j<4;j++){
            scanf("%d", &stu[i].sub[j]);
            stu[i].total += stu[i].sub[j];
        }
        stu[i].ave=(float)stu[i].total/4;
    }


    for(i=0;i<N;i++)
     {
       grade.sub[0]+=stu[i].sub[0];
       grade.sub[1]+=stu[i].sub[1];
       grade.sub[2]+=stu[i].sub[2];
       grade.sub[3]+=stu[i].sub[3];
    }
  for(i=0;i<4;i++)
  {
      ave[i]=(float)grade.sub[i]/N;
  }
    for(i=1;i<N;i++)
    {
        for(j=0;j<N-i;j++)
        {
          if(stu[j].ave<stu[j+1].ave)
          {
             a=stu[j];
             stu[j] = stu[j+1];
             stu[j+1] = a;
          }
        }
    }

    printf("        学生的平均分排名   \n");
    printf("------------------------------\n");
    for(i=0;i<N;i++)
        printf("%-10s  %-10s   %.2f\n",stu[i].id,stu[i].name,stu[i].ave);
    printf("******************************\n");
    printf("******************************\n");
    printf("        每门课的平均分为      \n");
    printf("———————————————\n");
    printf("The average of SUB1:  %.2f  \n",ave[0]);
    printf("The average of SUB2:  %.2f  \n",ave[1]);
    printf("The average of SUB3:  %.2f  \n",ave[2]);
    printf("The average of SUB4:  %.2f  \n",ave[3]);
    printf("\n\n");
    printf("OUTPUT：\n");
    f1 = fopen("stud.data","w");
    for(i=0;i<N;i++)
    {
        fprintf(f1,"%s %s %d %d %d %d %f",stu[i].id,stu[i].name,stu[i].sub[0],stu[i].sub[1],stu[i].sub[2],
            stu[i].sub[3],stu[i].ave);
    }
    fclose(f1);
    fprintf(stdout,"\n\n");

    f1 = fopen("stud.data","r");
    printf("ID         NAME      SUB1  SUB2  SUB3  SUB4  AVEARGE\n");
    for(i=0;i<N;i++)
    {
        fscanf(f1,"%s %s %d %d %d %d %f",stu[i].id,stu[i].name,&stu[i].sub[0],&stu[i].sub[1],&stu[i].sub[2],
            &stu[i].sub[3],&stu[i].ave);
        fprintf(stdout,"%s %s %5d %5d %5d %6d %5.2f\n",stu[i].id,stu[i].name,stu[i].sub[0],
            stu[i].sub[1],stu[i].sub[2],stu[i].sub[3],stu[i].ave);
    }
    fclose(f1);


}

如果多行显示的话，ID 除了第一个全部变成了存储的地址。