C语言结合链表

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

struct node {
   int data;
   struct node *next;
};

struct node *even = NULL;
struct node *odd = NULL;
struct node *list = NULL;

//Create Linked List
void insert(int data) {
   // Allocate memory for new node;
   struct node *link = (struct node*) malloc(sizeof(struct node));
   struct node *current;

   link->data = data;
   link->next = NULL;

   if(data%2 == 0) {
      if(even == NULL) {
         even = link;
         return;
      } else {
         current = even;

         while(current->next != NULL)
         current = current->next;

         // Insert link at the end of the list
         current->next = link; 
      }

   } else {
      if(odd == NULL) {
         odd = link;
         return;
      } else {
         current = odd;

         while(current->next!=NULL)
            current = current->next;

         // Insert link at the end of the list
         current->next = link; 
      }
   }
}

void display(struct node *head) {
   struct node *ptr = head;

   printf([head] =>);

   while(ptr != NULL) {        
      printf( %d =>,ptr->data);
      ptr = ptr->next;
   }

   printf( [null]\n);
}

void combine() {
   struct node *link;

   list = even;
   link = list;

   while(link->next!= NULL) {
      link = link->next;
   }

   link->next = odd;
}

int main() {
   int i;

   for(i = 1; i <= 10; i++)
      insert(i);

   printf(Even : );
   display(even);

   printf(Odd  : );
   display(odd);

   combine();

   printf(Combined List :\n);
   display(list);

   return 0;
}