linked list - segmenation fault error in my linkedList -C -

i put few pieces of code make linked list adds head(has special function) , in middle(also special function). problem is, need provide program numbers , insert them nodes in linkedlist. however, display function(to display tree of nodes) gives segmentation fault , taking values in without display function. i'm new malloc suspect problem there? thanks

#include<stdio.h> #include<stdlib.h>  /*linkedlist struct*/ struct node {         int data;         struct node *next;         };     /*inserting head-node*/ struct node *insert_head(struct node *head, int number) {     struct node *temp;     temp = malloc(sizeof(struct node));     if(temp == null)     {         printf("not enough memory\n");         exit(1);     }      temp->data = number;     temp->next = head;     head = temp;     return head;  }     /*inserting inside list*/ void after_me(struct node *me, int number) {     struct node *temp;     temp = malloc(sizeof(struct node));     if(temp == null)     {         printf("not enough memory\n");         exit(1);     }      temp->data = number;      temp->next = me->next;     me->next = temp; }     /*printing list*/ void display(struct node *head) {     struct node *moving_ptr = head;     while(moving_ptr != null)     {         printf("%d-->",moving_ptr->data);         moving_ptr = moving_ptr->next;      } }    int main() {     int index;     struct node *head;     struct node *previous_node;      scanf("%d", &index);     while(index > 0)     {           /*allocating in list */         if(head == null)             head = insert_head(head,index);         else         if((head != null) && (index <= (head->data)))             {                 struct node *temp;                 head->next = temp;                 temp->next = head;/*try insert head func.*/             }         else         if((head != null) && (index > (head->data)))         {             previous_node->data = index-1;             after_me(previous_node,index);         }          scanf("%d", &index);      }          display(head);     } 

i suggest follows.

#include <stdio.h> #include <stdlib.h>  struct node {     int data;     struct node *next; }; //aggregated 1 place     struct node *new_node(int number){     struct node *temp;     if(null == (temp = malloc(sizeof(*temp)))){         printf("\nnot enough memory\n");         exit(1);     }     temp->data = number;     temp->next = null;     return temp; }  struct node *insert_head(struct node *head, int number) {     struct node *temp = new_node(number);      temp->next = head;     return temp; }  void after_me(struct node *me, int number){     struct node *temp = new_node(number);      temp->next = me->next;     me->next = temp; } void display(struct node *head){     struct node *moving_ptr = head;     while(moving_ptr != null){         printf("%d", moving_ptr->data);         if(moving_ptr = moving_ptr->next)             printf("-->");     }     putchar('\n'); }  struct node *insert(struct node *me, int number){     if(me){         if(number <= me->data){             me = insert_head(me, number);         } else {             me->next = insert(me->next, number);         }     } else {         me = new_node(number);     }     return me; }  void release(struct node *list){//of course, able replace simple loop(e.g while-loop).     if(list){         release(list->next);         free(list);     } }  int main(void){     struct node *head = null;     int index;      while(1==scanf("%d", &index) && index > 0){         head = insert(head, index);     }     display(head);     release(head);     return 0; }