这是个双向链表的C程序，谁能解释下他的步骤的含义，不胜

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

typedef struct node{
float data;
struct node *pre;
struct node *next;
}*DoubleNode;

void sort_DoubleNode(DoubleNode &head, float data)
{
DoubleNode node = (DoubleNode)malloc(sizeof(struct node));
DoubleNode p,q;
node->data = data;
if(head == NULL)
{
head = node;
head->next = NULL;
head->pre = NULL;
return;
}

p = head;
while(p != NULL && p->data < data)
{
q = p;
p = p->next;
}
if(p == head)
{
node->next = head;
node->pre = NULL;
head ->pre = node;
head = node;
}
else{
q->next = node;
node->pre = q;
node->next = p;
if(p != NULL) p->pre = node;
}
}

void out_DoubleNode(DoubleNode &head)
{
DoubleNode p = head;
while(p != NULL)
{
printf("%.4f ", p->data);
p = p->next;
}
printf("/n");
}

void main()
{
int n;
float data;
DoubleNode head = NULL;
scanf("%d", &n);

for(int i=0; i<n; ++i)
{
scanf("%f", &data);
sort_DoubleNode(head, data);
}

out_DoubleNode(head);
}
/*
15
23.4 4.5 56 67 7.5 90 8.97 90.6 25.6 145
856 10.2 0.36 54.6 56.1
*/