Convert binary tree to array in c - c

Question

I want to convert a binary tree to an array using C. I tried but was unsuccessful.
My binary tree contains the following elements (preorder)
4 3 5 10 8 7
but my array contains (after sorting)
4 4 5 7 8 10
Any help would be greatly appreciated. My current code look like this:
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
typedef struct tree
{
int data;
struct tree *left;
struct tree *right;
}tree;
int AddToArray(tree *node, int arr[], int i);
tree *CreateNode(int data);
tree *Insert(tree *node, int data);
void PrintPreorder(tree *node);
int count(tree *node);
int compare(const void * a, const void * b);
//---------------------------------------------------------------------------
int main()
{
int i;
int size;
int *arr=NULL;
tree *root=NULL;
printf("***TEST PROGRAM***\n");
root = Insert(root, 4);
root = Insert(root, 3);
root = Insert(root, 5);
root = Insert(root, 10);
root = Insert (root, 8);
root = Insert (root, 7);
size = count(root);
printf("\n***BINARY TREE (PREORDER)***\n");
PrintPreorder(root);
printf("\nThe binary tree countain %d nodes", size);
printf("\n\n***ARRAY***\n");
arr = calloc(size, sizeof(int));
AddToArray(root, arr, 0);
qsort(arr,size,sizeof(int),compare);
for (i=0; i<size; i++)
{
printf("arr[%d]: %d\n", i, arr[i]);
}
}
//---------------------------------------------------------------------------
int compare(const void * a, const void * b)
{
return ( *(int*)a - *(int*)b );
}
int AddToArray(tree *node, int arr[], int i)
{
if(node == NULL)
return i;
arr[i] = node->data;
i++;
if(node->left != NULL)
AddToArray(node->left, arr, i);
if(node->right != NULL)
AddToArray(node->right, arr, i);
arr[i] = node->data;
i++;
}
tree *CreateNode(int data)
{
tree *node = (tree *)malloc(sizeof(tree));
node -> data = data;
node -> left = node -> right = NULL;
return node;
}
tree *Insert(tree *node, int data)
{
if(node==NULL)
{
tree *temp;
temp = CreateNode(data);
return temp;
}
if(data >(node->data))
{
node->right = Insert(node->right,data);
}
else if(data < (node->data))
{
node->left = Insert(node->left,data);
}
/* Else there is nothing to do as the data is already in the tree. */
return node;
}
void PrintPreorder(tree *node)
{
if(node==NULL)
{
return;
}
printf("%d ",node->data);
PrintPreorder(node->left);
PrintPreorder(node->right);
}
int count(tree *node)
{
int c = 1;
if (node == NULL)
return 0;
else
{
c += count(node->left);
c += count(node->right);
return c;
}
}

Answer 1

Change your AddToArray method to this:
int AddToArray(tree *node, int arr[], int i)
{
if(node == NULL)
return i;
arr[i] = node->data;
i++;
if(node->left != NULL)
i = AddToArray(node->left, arr, i);
if(node->right != NULL)
i = AddToArray(node->right, arr, i);
return i;
}
What was happening was that your recursive calls were changing the value of i (the index where you were supposed to insert the following element), but your recursion wasn't changing the value of i in the iteration that actually invoked the recursion. Updating i with the value returned by AddToArray fixes this.

Answer 2

Cause that i is not treated in a unified manner.
AddToArray replace with
void AddToArray(tree *node, int arr[], int *i){
if(node == NULL)
return ;
arr[*i] = node->data;
++*i;
AddToArray(node->left, arr, i);
AddToArray(node->right, arr, i);
}
and call i=0; AddToArray(root, arr, &i); at main.

Answer 3

The two lines of code int AddToArray
arr[i] = node->data;
i++;
Are appearing twice at each level of recursion. My guess is that every value in the tree is being written to the array twice and they over lap each other. but the root is the final value to be written twice so it is the only noticeable one.
Just remove the duplicate call at the bottom of the function.

Answer 4

int TreeToArray (struct node *tree, int *arr, int i)
{
if (tree == NULL) return i;
if (tree->left != NULL) i = TreeToArray(tree->left, arr, i);
arr[i] = tree->Value;
i++;
if (tree->right != NULL) i = TreeToArray(tree->right, arr, i);
return i;
}