Complete Binary Tree and Traversals

Implement a C program to construct a Complete Binary Tree and also display the elements in the tree using Inorder , Preorder and Postorder traversals.
A complete binary tree is a binary tree in which every level, except possibly the last, is completely filled, and all nodes are as far left as possible.

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

struct tree
{
    int data;
    struct tree *right,*left;
};

struct queue
{
    int front, rear;
    int size;
    struct tree* *array;
};

struct tree* newNode(int data);
struct queue* createQueue(int size);
void enqueue(struct tree *root, struct queue* queue);
struct tree* dequeue(struct queue* queue);
void insert(struct tree **root, int data, struct queue* queue);
void inorder(struct tree *);
void preorder(struct tree *);
void postorder(struct tree *);
  
int main()
{
    struct tree* root = NULL;
  char ans[3];
  int data;
    struct queue* queue = createQueue(50);
 do
 {
  printf("Enter the element to be inserted in the tree\n");
            scanf("%d",&data);          
        insert(&root, data, queue);
    printf("Do you want to insert another element?\n");
              scanf("%s",ans);
         } while (strcmp(ans,"yes") ==0); 
 
 printf("Inorder Traversal : The elements in the tree are");
            inorder(root);
            printf("\n");
            printf("Preorder Traversal : The elements in the tree are");
            preorder(root);
   printf("\n");
            printf("Postorder Traversal : The elements in the tree are");
            postorder(root);
      return 0;
}

struct tree* newNode(int data) 
{
 struct tree *nn = (struct tree*)malloc(sizeof(struct tree));
 nn->data = data;
 nn->left = NULL;
 nn->right = NULL;
 return nn;
}

struct queue* createQueue(int size)
{
  struct queue* queue = (struct queue*)malloc(sizeof(struct queue));
  queue->size = size;
  queue->front = -1;
  queue->rear = -1;
  queue->array = (struct tree**)malloc(size*sizeof(struct tree*));
  return queue;
}

void insert(struct tree **root, int data, struct queue* queue)
{
    struct tree *temp = newNode(data);
    if(*root == NULL)
        *root = temp;
    else{
        struct tree *front = queue->array[queue->front];
        if(front->left==NULL)
            front->left = temp;
        else if(front->right == NULL)
            front->right = temp;
        if(front->left!=NULL && front->right!=NULL)
            dequeue(queue);
    }
    enqueue(temp,queue);
}

void enqueue(struct tree *root, struct queue* queue)
{
    if(queue->rear==queue->size-1)
        return;
    queue->array[++queue->rear] = root;
    if(queue->front == -1)
        queue->front++;
}
 
struct tree* dequeue(struct queue* queue)
{
    if(queue->front==-1)
        return NULL;
    struct tree *temp = queue->array[queue->front];
    if(queue->front==queue->rear)
    queue->rear = queue->front = -1;
    else
    queue->front++;
    return temp;
}

void inorder(struct tree *temp) {
    if(temp!=NULL){
    inorder(temp->left);
    printf(" %d",temp->data);
    inorder(temp->right);
}
}

void preorder(struct tree *temp) {
    if(temp!=NULL){
     printf(" %d",temp->data);
     preorder(temp->left);
     preorder(temp->right);
}
}
 

void postorder(struct tree *temp) {
    if(temp!=NULL){
    postorder(temp->left);
    postorder(temp->right);
    printf(" %d",temp->data);
}
}