代码：

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

#define m 3
struct student{
    long cardnum;;
    char name[20];
    char academy[20];
    long class_num;
};

void input(struct student stu[m])
{
    int j,i=1;
    for(j=0;j<m;j++)
    {
        printf("请输入第%d个同学的卡号:",i);
        scanf("%ld",&stu[j].cardnum);
        printf("请输入第%d个同学的姓名:",i);
        scanf("%s",stu[j].name);
        printf("请输入第%d个同学的院系:",i);
        scanf("%s",stu[j].academy);
        printf("请输入第%d个同学的班级:",i);
        scanf("%ld",&stu[j].class_num);
        i++;
        printf("--------------------------\n");
    }
}

void quicksort(struct student stu[m],int left,int right)
{
    int i,j;
    struct student p;
    if(left<right)
    {
        i=left+1;
        j=right;

        while(i<j)
        {
            if(stu[i].cardnum > stu[left].cardnum)
            {
               p=stu[i];
               stu[i]=stu[left];
               stu[left]=p;
               j--;
            }
            else
            {
                i++;
            }
        }
        if(stu[i].cardnum >= stu[left].cardnum)
        {
            i--;
        }
        p=stu[left];
        stu[left]=stu[i];
        stu[i]=p;

        quicksort(stu,left,i);
        quicksort(stu,j,right);
    }
}

void sort(struct student stu[m])
{
    int i,j;
    struct student p;
    for(i=0;i<m;i++)
    {
        for(j=i+1;j<m;j++)
        {
            if(strcmp(stu[i].name,stu[j].name)>0)
            {
                p=stu[i];
                stu[i]=stu[j];
                stu[j]=p;
            }
        }
    }
}

int twice_find(struct student stu[m],int key)
{
    int low,high=m-1,mid;
    while(low<=high)
    {
        mid=(low+high)/2;
        if(stu[mid].cardnum == key) return mid;
        if(stu[mid].cardnum>key)
            high=mid-1;
        else
            low=mid+1;
    }
    return -1;
}
void display(struct student stu[m])
{
    int i;
    printf("学生信息如下:\n");
    printf("--------------------------\n");
    for(i=0;i<m;i++)
    {
        printf("卡号:%ld\n姓名:%s\n院系:%s\n班级:%ld\n",stu[i].cardnum,stu[i].name,stu[i].academy,stu[i].class_num);
        printf("--------------------------\n");
    }
}

int main()
{
    struct student stu[m];
    int i,key,j;
    printf("请输入借书同学的信息:\n");
    printf("--------------------------\n");
    input(stu);
    printf("请选择你想要的功能:\n");
    printf("1.按照卡号进行排序。\n");
    printf("2.按照姓名进行排序。\n");
    printf("3.二分查找同学的信息。\n");
    printf("4.退出系统。\n");
    scanf("%d",&i);
    switch(i)
    {
    case 1:
        quicksort(stu,0,m-1);
        printf("排序结果为:\n");
        display(stu);
        break;
    case 2:
        sort(stu);
        printf("排序结果为:\n");
        display(stu);
        break;
    case 3:
        printf("请输入要查找的同学的卡号:");
        scanf("%d",&key);
        j=twice_find(stu,key);
        printf("卡号:%ld\n姓名:%s\n院系:%s\n班级:%ld\n",stu[j].cardnum,stu[j].name,stu[j].academy,stu[j].class_num);
        break;
    case 4:
        break;
    }
    return 0;
}