Sum of all the grandchild nodes of binary tree in c

C program for Sum of all the grandchild nodes of binary tree. Here more solutions.

// Include header file
#include <stdio.h>
#include <stdlib.h>
/*
    C program for
    Sum of nodes in binary tree whose grandparents exists
*/
// Binary Tree node
typedef struct TreeNode
{
	// Define useful field of TreeNode
	int data;
	struct TreeNode * left;
	struct TreeNode * right;
}TreeNode;

TreeNode * getTreeNode(int data)
{
	// Create dynamic memory of TreeNode
	TreeNode * ref = (TreeNode * ) malloc(sizeof(TreeNode));
	if (ref == NULL)
	{
		// Failed to create memory 
		return NULL;
	}
	// Set node value
	ref->data = data;
	ref->left = NULL;
	ref->right = NULL;
	return ref;
}
typedef struct BinaryTree
{
	// Define useful field of BinaryTree
	struct TreeNode * root;
}BinaryTree;

BinaryTree * getBinaryTree()
{
	// Create dynamic memory of BinaryTree
	BinaryTree * ref = (BinaryTree * ) malloc(sizeof(BinaryTree));
	if (ref == NULL)
	{
		// Failed to create memory 
		return NULL;
	}
	// Set initial tree root
	ref->root = NULL;
	return ref;
}

void preOrder(TreeNode * node)
{
	if (node != NULL)
	{
		// Print node value
		printf("  %d", node->data);
		// Visit left subtree
		preOrder(node->left);
		// Visit right subtree
		preOrder(node->right);
	}
}
int grandchildSum(TreeNode * node, int level)
{
	if (node != NULL)
	{
		int result = 0;
		if (level > 2)
		{
			// Get the node
			result = node->data;
		}
		// Visit left subtree and right subtree
		return result + 
          grandchildSum(node->left, level + 1) + 
          grandchildSum(node->right, level + 1);
	}
	else
	{
		return 0;
	}
}
int main()
{
	// Create new binary trees
	BinaryTree * tree = getBinaryTree();
	/*
	         4   
	        /  \                          
	       /    \    
	      12     7    
	     / \      \               
	    2   3      1
	       / \    / 
	      6   8  5
	     /        
	    9                        
	  ----------------
	  Constructing binary tree    
	*/
	// Add nodes
	tree->root = getTreeNode(4);
	tree->root->left = getTreeNode(12);
	tree->root->left->right = getTreeNode(3);
	tree->root->left->right->left = getTreeNode(6);
	tree->root->left->right->left->left = getTreeNode(9);
	tree->root->left->right->right = getTreeNode(8);
	tree->root->left->left = getTreeNode(2);
	tree->root->right = getTreeNode(7);
	tree->root->right->right = getTreeNode(1);
	tree->root->right->right->left = getTreeNode(5);
	// Display tree node
	printf("\n Tree Nodes ");
	preOrder(tree->root);
	// Find node sum
	// 2 + 3 + 6 + 9 + 8 + 1 + 5 = 34
	int result = grandchildSum(tree->root, 1);
	// Display result
	printf("\n Result : %d", result);
}

Output

 Tree Nodes   4  12  2  3  6  9  8  7  1  5
 Result : 34