C语言处理双向链表的排序问题

#include <stdio.h> 
#include <stdlib.h> 
typedef struct node{ 
	int data; 
	struct node *pre; 
	struct node *next; 
} Node;
int get_int(void);
Node* get_node(void);
void insert(Node*p,Node* new_node);
int 
main()
{
	Node * p;
	Node * head = (Node*)malloc(sizeof(Node));
	head->pre = NULL;
	head->next = get_node();
	head->next->pre = head;
	printf("please enter the number 'q' to quit:");
	while (1)
	{
		p = get_node();
		p->data = get_int();
		if (p->data ==0)
			break;
		insert(head,p);
	}
	while (head->next!=NULL)
	{
		printf("%d ",head->next->data);
		head->next = head->next->next;
	}
	return 0;
}
//得到整数
int
get_int(void)
{
	int input;
	char ch;
	while (scanf("%d",&input)!=1)
	{
		while((ch=getchar())!='\n')
			putchar(input);
		printf(" is not an integer.\nPlease enter an integer value,such as 25,-178,or 3;\n");
	}
	return input;
}
//向链表插入新链
void 
insert(Node*p,Node* new_node)
{
	if (p->next->data == 0)
	{
		p->next->data = new_node->data;
		return;
	}
	Node* scan = p->next;
	while (1)
	{
		if (scan->data < new_node->data)
		{
			if (scan->next != NULL)
				scan = scan->next;
			else
			{
				scan->next = new_node;
				new_node->pre = scan;
				break;
			}
		}
		else
		{
			new_node->pre = scan->pre;
			new_node->next = scan;
			scan->pre->next = new_node;
			scan->pre = new_node;
			break;
		}
	}
}
//获得新节点
Node* 
get_node(void)
{
	Node* new_node = (Node*)malloc(sizeof(Node));
	new_node->next = NULL;
	new_node->pre = NULL;
	new_node->data = 0;
	return new_node;
}