Assigning NULL to the head node in a linked list in C

Please see the full code below.

I have an initial array named arr. I'm using a linked list to store some indices via the append function. After I got the indices, I store them in linked list and use clearList to change the corresponding values to 0 (In this example arr[2] and arr[4]). Finally, I free the memory by calling freeList since i'm done with the linked list.

However, to be able to do same thing again and again, I need to set head to NULL whenever I call freeList. But I cannot. Any idea how to solve this? Thank you.

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

//Gurobi variables
GRBenv   *env = NULL;
GRBmodel *model = NULL;
//Gurobi variables

struct Node 
{ 
  int data; 
  struct Node *next;
  struct Node *end;
};

void append(struct Node** head_ref, int new_data) 
    { 
    struct Node *last = *head_ref;  
    struct Node* new_node = (struct Node*) malloc(sizeof(struct Node));  
    new_node->data  = new_data; 
    new_node->next = NULL;
    new_node->end = new_node;
    if (*head_ref == NULL) 
    { 
       *head_ref = new_node;
       //printf("  ..Init Append %d\n",new_data);
       return; 
    } 
    last = (*head_ref)->end; 
    last->next = new_node;  
    (*head_ref)->end=new_node;
    //printf("  ..Append %d\n",new_data);
    return; 
} 

void clearList(struct Node *node, double *arr) 
    { 
    int i;
    if(node!=NULL)
        {
        struct Node tmp;
        tmp=*(node->end);
        while (node != NULL) 
            {  
            i=node->data;
            arr[i]=0;
            //printf("   ..clear %d \n", node->data,(node->end)->data);
            node = node->next; 
            }
        }
    }

void freeList(struct Node *node) 
    { 
    struct Node *tmp,*hd;
    hd=node;
    while (node != NULL) 
        { 
        tmp=node;
        node = node->next; 
        //printf("  ..Free %d \n", tmp->data);      
        free(tmp);
        } 
    hd=NULL;
    }

int main (){
    Node *head;     
    double *arr = (double *) malloc(sizeof(double) * 10);
    for(int i=0;i<10;i++)
        arr[i]=i;

    head=NULL;
    printf("Head:  %s\n", head);
    append(&head,2);
    append(&head,4);
    clearList(head,arr);
    for(int i=0;i<10;i++)
        printf("No %d : %.2f\n",i,arr[i]);
    freeList(head);

    free(arr);

    printf("%s", head);
    getchar();
    return 0;
    }