Linked List in C

Doubly Linked List

  1 #include<stdio.h>
  2 #include<stdlib.h>
  3 
  4 typedef struct node{
  5     int val;
  6     struct node *prev, *next;
  7 }node;
  8 
  9 node *head = NULL;
 10 
 11 node* insert_after(node *n, int val){
 12     // insert_after next to current node
 13     node *newnode = (node*)malloc(sizeof(node));
 14     newnode->val = val;
 15     newnode->next = NULL;
 16     newnode->prev = NULL;
 17     if(n == NULL){
 18         n = newnode;
 19     }else{
 20         newnode->next = n->next;
 21         newnode->prev = n;
 22 
 23         if(n->next != NULL) n->next->prev = newnode;
 24         n->next = newnode;
 25     }
 26     return n;
 27 }
 28 
 29 node* insert_before(node *n, int val){
 30     if(n == NULL){
 31         n = insert_after(n, val);
 32     }else{
 33         node *prev = n->prev;
 34         if(prev == NULL){
 35             // insert at head return new head
 36             prev = insert_after(prev, val);
 37             prev->next = n;
 38             n->prev = prev;
 39             n = prev;
 40         }else{
 41             prev = insert_after(prev, val);
 42         }
 43         
 44     }
 45     return n;
 46 }
 47 
 48 node* remove(node *n){
 49     node *removenode = n;
 50     node *returnnode = NULL;
 51     if(n->prev != NULL){
 52         n->prev->next = n->next;
 53         returnnode = n->prev;
 54     }
 55     if(n->next != NULL){
 56         n->next->prev = n->prev;
 57         returnnode = n->next;
 58     }
 59     free(removenode);
 60     return returnnode;
 61 }
 62 
 63 void print_list(node *head){
 64     printf("List : ");
 65     if(head == NULL){
 66         printf("--EMPTY--");
 67     }
 68     while(head != NULL){
 69         printf("%d ", head->val);
 70         head = head->next;
 71     }
 72 
 73     printf("\n");
 74 }
 75 
 76 int main(){
 77     head = insert_after(head, 1);
 78     print_list(head);
 79     head = insert_after(head, 2);
 80     print_list(head);
 81     head = insert_after(head, 3);
 82     print_list(head);
 83     head = insert_before(head, 4);
 84     print_list(head);
 85     head = insert_before(head, 5);
 86     print_list(head);
 87 
 88     node *temp = head->next->next;
 89     temp = insert_after(temp, 6);
 90     print_list(head);
 91 
 92     head = remove(head);
 93     print_list(head);
 94     head = remove(head);
 95     print_list(head);
 96     head = remove(head);
 97     print_list(head);
 98 
 99     temp = head->next;
100     temp = remove(temp);
101     print_list(head);
102 
103     temp = head->next;
104     temp = remove(temp);
105     print_list(head);
106 
107 
108     head = remove(head);
109     print_list(head);
110 }