This program converts a BST to Linked list using queue

tree_to_list_using_queue.c

#include<stdio.h>
#include<stdlib.h>
#include<math.h>
 
struct node{
        int value;
        struct node *left;
        struct node *right;
};
typedef struct node Node;
 
Node * create_node(int value){
        Node * temp =  (Node *)malloc(sizeof(Node));
        temp->value = value;
        temp->right= NULL;
        temp->left = NULL;
        return temp;
}
Node * addNode(Node *node, int value){
        if(node == NULL){
                return create_node(value);
        }
        else{
          if (node->value > value){
                node->left = addNode(node->left, value);
          }
          else{
                node->right = addNode(node->right, value);
          }
        }
        return node;
}

void treeToList(Node *node){

        Queue *queue = NULL;
        Node * last = NULL;
        if(node == NULL)
                return ;

        enqueue(&queue, node);
        while(!isEmpty(queue)){
        /* Take the first element and put both left and right child on queue */
                node = front(queue);
                if(node->left)
                        enqueue(&queue, node->left);
                if(node->right)
                        enqueue(&queue, node->right);
                if(last != NULL)
                        last->right = node;
                node->left = last;
                last = node;
                dequeue(&queue);

        }

} 
/* Driver program for the function written above */
int main(){
        Node *root = NULL;
       //Creating a binary tree
        root = addNode(root,30);
        root = addNode(root,20);
        root = addNode(root,15);
        root = addNode(root,25);
        root = addNode(root,40);
        root = addNode(root,37);
        root = addNode(root,45);
        
        treeToList(root);
        
        return 0;
}