[c language] use the reverse order output of the linked list (bidirectional linked list)

Topic content ：

Your program will read in a series of positive integers , I don't know the number of positive integers in advance , Once you read it -1, It means the end of input . then , Output the number read in the reverse order of the input , Not including the end of the last logo -1.

Input format :

A series of positive integers , Input -1 End of the said ,-1 Not part of the input data .

Output format ：

Output all integers in the reverse order of input , Each integer is followed by a space to distinguish it from the following integer , There is also a space after the last integer .

sample input ：

1 2 3 4 -1

sample output ：

4 3 2 1 

The time limit ：500ms Memory limit ：32000kb

Ideas ： Use Double linked list , Record the location of the last node , Then visit the precursor nodes one by one and output . I wrote a lot of things I didn't understand, but the result seemed to be right , People are numb .

         Need to define include Pointer to the previous node former And a pointer to the next node next The node of

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

typedef struct NODE{
	int data;
	struct NODE * next; 
	struct NODE * former; 

}numset; // Each node of the linked list , Including data , Previous node pointer , Next node pointer 

typedef struct List{
	numset* head;
	numset* end;
	numset* now; 
	int size;
}list; // To facilitate the transfer of linked lists into functions , The structure of the definition . Accessible header node , Tail node , Current node , Chain table size （ It doesn't work ）



void read(list* );


void put(list* );


int main(){
	list pset;// amount to  numset* pset;

	pset.head=NULL;
	pset.end=NULL;
	pset.now=NULL;
	pset.size=0;// Initialize linked list . amount to pset=NULL;

	read(&pset);

	put(&pset);

	//free(pset);// When should I use free... I don't understand , Put it here in the back put() In the function free 了 
	return 0;
} 

void read(list* p){
	int n;
	//numset* position=(numset*)malloc(sizeof(numset));
	numset* position=NULL;// Save the current node A1 The location of , When processing to the next node A2, You can assign this position to A2 The forerunner of . Now there are no nodes , The position pointer points to null .
// When do you want to apply for space .. I don't quite understand 
	
	while(scanf("%d",&n) && n!=-1){
		
		
		p->now=(numset*)malloc(sizeof(numset));
        p->now->data=n;

		p->now->former=position;// Hang the precursor node to the previously saved location 
				
		if(!p->head){
			p->head=p->now;// If the head node pointer points to null , Then hang the head pointer on the node just entered 
		}
		
		p->end=p->now;// Hang the tail pointer on the latest input node 

		p->size++;

	//	printf("now=%d\n",p->now->data); // Test use . Output the node just read 
		
		position=p->now;// Save the current node A1 The location of , When processing to the next node A2, You can assign this position to A2 The forerunner of 
		p->now=p->now->next;
			
		
	//		printf("former=%d\n",p->now->former); // Test use . Why does it always output the same value here ？？？ I don't understand 
		
	}
}


void put(list* p){
		
	while(p->end){
		printf("%d ",p->end->data);
	//	if(p->end->former) 	//printf("former=%d\n",p->end->former->data); Test use , The precursor values output here are all right ah ah why ... Crazy ing
		free(p->end);
		p->end=p->end->former;
		
		
		
	}
}

solve ... Why does the output of the precursor node in the two functions get different results ？？