c: 鏈表的增刪改查的操作

#include<stdio.h>
#include<stdlib.h>
#define LEN sizeof(struct student)
struct student{
	int num;
	double score;
	struct student *next;
};

//創建一個鏈表
struct student * create(void){
	struct student *p1,*p2,*head;
	int n = 0;
	p1 = p2 = (struct student *)malloc(LEN);
	scanf("%d%lf",&(p1->num),&(p1->score));
	while(p1->num!=0){
		n++;
		if(n==1){
			head = p1;
		}else{
			p2 = p1;
		}
		p1 = (struct student *)malloc(LEN);
		scanf("%d%lf",&(p1->num),&(p1->score));
		p2->next = p1;
	}
	
	p2->next = NULL;
	return head;
}
struct student *delw(struct student *start,int num){
	struct student *p1,*p2;
	//鏈表為空
	if(start==NULL){
		printf("\nlist null!\n");
		return NULL;
	}
	p1 = start;
	p2 = NULL;
	//鏈表不為空
	//鏈表只有一個元素，且即為所要找的元素
	/*if(p1->next==NULL&&p1->num == num){
		printf("there is only one element and that is it!");
		return NULL;
	}*/
	while(p1->next!=NULL&&p1->num!=num){
		p2 = p1;
		p1 = p1->next;
	}
	
	if(num == p1->num){
		if(p1 == start){
			return start->next;
		}else{
			p2->next = p1->next;
		}
	}else{
		printf("number not found!");
	}
	
	return start;
}

struct student *del(struct student *head,long num){

	struct student *p1, *p2;
	//鏈表為空
	if(head == NULL){
		printf("\nlist null!\n");
		return head;
	}
	//鏈表不為空
	p1 = head;
	while(p1->next!=NULL&&num!=p1->num){
		p2 = p1;
		p1 = p1->next;
	}
	if(num == p1->num){
		if(p1 == head){
			head = p1->next;
		}else{
			p2->next = p1->next;
			printf("delete:%ld\n",num);
		}
	}else
			printf("%ld not been found!\n",num);
	return head;

}
//刪除一個節點
struct student * deleteNode(struct student *start,int num){
	struct student *p1, *p2,*before,*after;
	//空表
	if(start==NULL){
		printf("the linktable is null");
		return NULL;
	}
	p1 = p2 = start;
	//只有一個節點
	if(start->next==NULL){
		if(start->num==num){
			return NULL;
		}
	}
	//鏈表不為空(兩個以上的節點)
	//1:鏈表的第一個即為所要找的
	if((start->num == num)&&(start->next!=NULL)){
		return start->next;
	}
	while(p1!=NULL){
		if(p1->num==num){
			before = p2;
			after = p1->next;
		}
		p2 = p1;
		p1 = p1->next;
	}
	before->next = after;
	return start;
}

struct student * insert(struct student *head,struct student *stu){
	struct student *p1,*p2, *p0;
	p1 = head;
	p0 = stu;
	
	//鏈表為空
	if(head == NULL){
		head = p0;
		p0->next = NULL;
		printf("the link is null\n");
		return NULL;
		//鏈表不為空，比較num，（如22， 33， 55），44應插入至33后面
	}else{
		//一個元素
		//printf("head.next is not null");
		//兩個以上元素: 22 55 88
		while(p1->num<p0->num&&p1->next!=NULL){
			p2 = p1;
			p1 = p1->next;
		}

		if(p1->num>p0->num){//
			if(p1==head){//p0排到最前
				head = p0;
				p0->next = p1;
			}else{
				//p0排到中間
				p2->next = p0;
				p0->next = p1;
			}
		}else{//p0排到最后
			p1->next = p0;
			p0->next = NULL;
		}

		return head;
	}
	

}

void printLink(struct student *p){
	struct student *p_afterDeal = p;
	p_afterDeal = p;
	while(p_afterDeal!=NULL){
		printf("num = %d, score = %lf\n",p_afterDeal->num,p_afterDeal->score);
		p_afterDeal = p_afterDeal->next;  
	}
}
int main(void){
	
	struct student * p_std, * p_afterDel,*p,*p_afterInsert; 
	struct student newstd = {44,44.4,NULL};
	//創建一個鏈表
	printf("創建一個鏈表：\n");
	p_std = create();
	printf("創建的鏈表如下：\n");
	printLink(p_std);
	//插入一個節點
	printf("插入一個節點：44\n");
	p = &newstd;
	p_afterInsert = insert(p_std,p);
	printf("插入一個節點后的列表如下：\n");
	printLink(p_afterInsert);
	//刪除一個節點
	printf("刪除一個節點：44\n");
	p_afterDel = deleteNode(p_afterInsert,44);
	printf("刪除一個節點后的列表如下：\n");
	printLink(p_afterDel);
	system("pause");
}