学生信息链表，建立，插入，删除，遍历，查找，修改，最大（小）值，平均

/【例11-10】建立一个学生成绩信息（包括学号、姓名、成绩）的单向链表，学生数据按学号由小到大顺序排列，要求实现对成绩信息的插入、修改、删除和遍历操作。/

/* 用链表实现学生成绩信息的管理 */

include<stdio.h>

include<stdlib.h>

include<string.h>

struct stud_node{
int num;
char name[20];
int score;
struct stud_node next;
};
struct stud_node create_stu_doc(); /* 新建链表 /
struct stud_node insertdoc(struct stud_node * head, struct stud_node stud); / 插入 /
struct stud_node deletedoc(struct stud_node * head, int num); /* 删除 /
void print_stu_doc(struct stud_node head); /* 遍历 */

struct stud_node * find(struct stud_node * head, int num); /查找/
struct stud_node * modify(struct stud_node * head, int num, int score); /修改成绩/
struct stud_node * max(struct stud_node * head); /求最高分数的学生记录/
struct stud_node * min(struct stud_node * head); /求最低分数的学生记录/
double ave(struct stud_node * head); /求平均分/
void save(struct stud_node * head);
struct stud_node *read();

typedef struct stud_node *lnode;
lnode head,p;

int main(void)
{
struct stud_node head=null, p;
int choice, num, score;
char name[20];
int size = sizeof(struct stud_node);

do{
printf("1:create 2:insert 3:delete 4:print 5:modify 6:find 7:max 8:save 9:read 10:min 0:exit\n");
scanf("%d", &choice);
switch(choice){
case 1:
head = create_stu_doc();
break;
case 2:
printf("input num,name and score:\n");
scanf("%d%s%d", &num,name, &score);
p = (struct stud_node *) malloc(size);
p->num = num;
strcpy(p->name, name);
p->score = score;
head = insertdoc(head, p);
break;
case 3:
printf("input num:\n");
scanf("%d", &num);
head = deletedoc(head, num);
break;
case 4:
print_stu_doc(head);
break;
case 5:
printf("input num:\n");
scanf("%d", &num);
printf("input score:\n");
scanf("%d", &score);
head=modify(head,num,score);
break;
case 6:
printf("input num:\n");
scanf("%d", &num);
p=find(head,num);
if(p!=null)
printf("%d\t%s\t%d \n", p->num, p->name, p->score);
else
printf("not found %d\n",num);
break;
case 7:
p=max(head);
if(p!=null)
printf("%d\t%s\t%d \n", p->num, p->name, p->score);
else
printf("not found\n");
break;
case 8:
save(head);
break;
case 9:
head=read();
break;
case 10:
p=min(head);
if(p!=null)
printf("%d\t%s\t%d \n", p->num, p->name, p->score);
else
printf("not found\n");
break;
case 0:
break;
}
}while(choice != 0);

return 0;
}

/新建链表/
struct stud_node * create_stu_doc()
{
struct stud_node * head,*p;
int num,score;
char name[20];
int size = sizeof(struct stud_node);

head = null;
printf("input num,name and score:\n");
scanf("%d%s%d", &num,name, &score);
while(num != 0){    /* 学号0表示输入结束，且学号0对应的姓名和成绩都要输入 */ 
   p = (struct stud_node *) malloc(size);
   p->num = num;
   strcpy(p->name, name);
   p->score = score;
   head = insertdoc(head, p);    /* 调用插入函数 */
   scanf("%d%s%d", &num, name, &score);

}
return head;
}

/* 插入操作 /
struct stud_node insertdoc(struct stud_node * head, struct stud_node stud)
{
struct stud_node ptr ,ptr1, ptr2;

ptr2 = head; 
ptr = stud;                 /* ptr指向待插入的新的学生记录结点 */

if(head == null){ /* 原链表为空时的插入 */ 
    head = ptr;             /* 新插入结点成为头结点 */
    head->next = null;
}
else{             /* 原链表不为空时的插入 */
    while((ptr->num > ptr2->num) && (ptr2->next != null)){
        ptr1 = ptr2;        /* ptr1, ptr2各后移一个结点 */
        ptr2 = ptr2->next;
    }
    if(ptr->num <= ptr2->num){  
        if(head == ptr2)  head = ptr;/* 新插入结点成为头结点 */
        else ptr1->next = ptr;       /* 在ptr1与ptr2之间插入新结点 */
        ptr->next = ptr2;
    }
    else{                            /* 新插入结点成为尾结点 */
        ptr2->next = ptr;
        ptr->next = null; 
    } 
}
return head;

}

/* 删除操作 /
struct stud_node deletedoc(struct stud_node * head, int num)
{
struct stud_node ptr1, ptr2;

if(head == null)  /*链表空 */
    return null;
else if(head->num == num){
    /* 要被删除结点为表头结点 */
    while(head != null && head->num == num){  
        ptr2 = head;
        head = head->next;
        free(ptr2);
    }
}
else{
    /* 要被删除结点为非表头结点  */
    ptr1 = head;
    ptr2 = head->next; /*从表头的下一个结点搜索所有符合删除要求的结点 */
    while(ptr2 != null){
        if(ptr2->num == num){   /* ptr2所指结点符合删除要求 */
            ptr1->next = ptr2->next;
            free(ptr2); 
        }
        else 
            ptr1 = ptr2;       /* ptr1后移一个结点 */
        ptr2 = ptr1->next;    /* ptr2指向ptr1的后一个结点 */
    }
}

return head;

}

/遍历操作/
void print_stu_doc(struct stud_node * head)
{
struct stud_node * ptr;

if(head == null){
    printf("\nno records\n");
    return;
}
printf("\nthe students' records are: \n");
printf("num\tname\tscore\n");
for(ptr = head; ptr != null; ptr = ptr->next)
    printf("%d\t%s\t%d \n", ptr->num, ptr->name, ptr->score);

}

struct stud_node * find(struct stud_node * head, int num) /查找/
{
struct stud_node *ptr;

if(head==null)
    return null;
else
{
    for(ptr=head;ptr!=null;ptr=ptr->next)/*for循环从head开始到null循环*/ 
        if(ptr->num==num)
            break;
            return ptr;
}

}

struct stud_node * modify(struct stud_node * head, int num, int score)/修改通过查找学号修改成绩/
{
struct stud_node *ptr;

if(head==null)
    return null;
else
{
    for(ptr=head;ptr!=null;ptr=ptr->next)
        if(ptr->num==num)
        {
            ptr->score=score;
            break;
        }
                
    return head;
}

}

struct stud_node * max(struct stud_node * head)
{
struct stud_node maxp,ptr;

if(head==null)
    return null;
else
{
    maxp=head;
    for(ptr=head->next;ptr!=null;ptr=ptr->next)
        if(maxp->score<ptr->score)
            maxp=ptr;
    
    return maxp;
}

}
struct stud_node * min(struct stud_node * head)
{
struct stud_node minp,ptr;

if(head==null)
    return null;
else
{
    minp=head;
    for(ptr=head->next;ptr!=null;ptr=ptr->next)
        if(minp->score>ptr->score)
            minp=ptr;
    
    return minp;
}

}

void save(struct stud_node * head)
{
file fp;
if((fp=fopen("data.txt","w")) == null){ /打开文件（套用）*/
printf("file open error!\n");
exit(0);
}

struct stud_node * ptr;

if(head == null){
    return;
}

for(ptr = head; ptr->next != null; ptr = ptr->next)
    fprintf(fp,"%d %s %d\n", ptr->num, ptr->name, ptr->score);
fprintf(fp,"%d %s %d", ptr->num, ptr->name, ptr->score);/*输出的最后没有换行*/
      
if( fclose(fp) ){/*关闭文件（套用）*/
    printf( "can not close the file!\n" );
    exit(0);
}   

}

struct stud_node read()
{
file fp;
if((fp=fopen("data.txt","r")) == null){
printf("file open error!\n");
exit(0);
}

struct stud_node * head,*tail,*p;
//int num,score;
//char  name[20];
int size = sizeof(struct stud_node);

head = tail=null;


while(!feof(fp)){   /* 读到结束标志结束 */ 
   p = (struct stud_node *) malloc(size);
   fscanf(fp,"%d%s%d", &p->num, p->name, &p->score);
   //head = insertdoc(head, p);    /* 调用插入函数 */
   p->next = null;
    if(head == null) 
        head = p;
    else  
        tail->next = p;
    tail = p;  

}

     if( fclose(fp) ){
    printf( "can not close the file!\n" );
    exit(0);
}

return head;

}