链表 c语言 数据结构问题

Question

请问：这段代码该怎么解释呢？（完整的代码在最下面）

    while (pre && p)
    {
        if(p->id < t->id)
        {
            pre = p;
            p = p->next;
        }else
            break;
    }
    if(p)
    {
        pre->next = t;
        t->next = p;
    }else
        pre->next = t;
    return head;
}
--------------------------
--------------------------
完整如下：

#include <stdio.h>
#include <stdlib.h>
struct Student
{
    int id;
    char name[20];
    int score;
    struct Student* next;
};
//创建链表，按学号排序插入
struct Student* createlist()
{
    int i,n;
    struct Student* head,*pre,*p,*t;
    head = (struct Student*)malloc(sizeof(struct Student));
    head->next = NULL;
    printf("请输入学生的个数：");
    scanf("%d",&n);
    for(i=0;i<n;i++)
    {
        t = (struct Student*)malloc(sizeof(struct Student));
        t->next = NULL;
        printf("请输入学生%d的学号：",i+1);
        scanf("%d",&t->id);
        printf("请输入学生%d的姓名：",i+1);
        scanf("%s",t->name);
        printf("请输入学生%d的成绩：",i+1);
        scanf("%d",&t->score);
        pre = head;
        p = pre->next;
        while (pre && p)
        {
            if(p->id < t->id)
            {
                pre = p;
                p = p->next;
            }else
                break;
        }
        if(p)
        {
            pre->next = t;
            t->next = p;
        }else
            pre->next = t;
    }
    return head;
}
//遍历显示
void show(struct Student* head)
{
    struct Student* p;
    if(head == 0) 
    {
        printf("链表为空\n");
        return;
    }
    p=head->next;
    while(p)
    {
        printf("学号：%d 姓名：%s 成绩：%d\n",p->id,p->name,p->score);
        p = p->next;
    }
}
//插入
struct Student* insert(struct Student* head)
{
    struct Student *pre,*p,*t;
    t = (struct Student*)malloc(sizeof(struct Student));
    t->next = NULL;
    printf("请输入学生的学号：");
    scanf("%d",&t->id);
    printf("请输入学生的姓名：");
    scanf("%s",t->name);
    printf("请输入学生的成绩：");
    scanf("%d",&t->score);
    pre = head;
    p = pre->next;
    while (pre && p)
    {
        if(p->id < t->id)
        {
            pre = p;
            p = p->next;
        }else
            break;
    }
    if(p)
    {
        pre->next = t;
        t->next = p;
    }else
        pre->next = t;
    return head;
}
//修改
struct Student* mod(struct Student* head)
{
    struct Student* p = head->next;
    int id;
    printf("请输入要修改信息的学生学号：");
    scanf("%d",&id);
    while(p)
    {
        if(p->id == id)
            break;
        else
            p = p->next;
    }
    printf("请输入学生的姓名：");
    scanf("%s",p->name);
    printf("请输入学生的成绩：");
    scanf("%d",&p->score);
    return head;
}
//删除
struct Student* del(struct Student* head)
{
    struct Student* p,*pre;
    int id;
    pre = head;
    p = head->next;
    printf("请输入要修改信息的学生学号：");
    scanf("%d",&id);
    while(p)
    {
        if(p->id == id)
            break;
        else
        {
            pre = p;
            p = p->next;
        }
    }
    if(p)
    {
        pre->next = p->next;
        free(p); p=0;
        printf("删除成功\n");
    }else
        printf("未找到该学号的学生\n");
    return head;
}
//释放内存
void release(struct Student* head)
{
    struct Student *p;
    while(head)
    {
        p = head->next;
        free(head);
        head = p;
    }
}
int main()
{
    struct Student* head =NULL;
    head = createlist();
    printf("当前链表数据为：\n");
    show(head);
    printf("插入数据：");
    head = insert(head);
    printf("插入数据后：\n");
    show(head);
    printf("修改数据：");
    head = mod(head);
    printf("修改数据后：\n");
    show(head);
    printf("删除数据\n");
    head = del(head);
    printf("删除数据后：\n");
    show(head);
    //释放内存
    release(head);
    return 0;
}
 

Answer 1

写注解里了，供参考

    while (pre && p)//找出比t所指向的id小的id，把pre指针指向最小id的地址
    {
        if(p->id < t->id)
        {
            pre = p;
            p = p->next;
        }else
            break;
    }
    if(p)//pre指向原t指针的位置，插入pre指向的数据
    {
        pre->next = t;
        t->next = p;
    }else
        pre->next = t;
    return head;
}