Pairwise swap leaf nodes in a binary tree

/*
    C Program 
    Pairwise swap leaf nodes in a binary tree
*/
#include <stdio.h>
#include <stdlib.h>

 // Tree Node
struct TreeNode
{
	int data;
	struct TreeNode *left;
	struct TreeNode *right;
};
// Binary Tree
struct BinaryTree
{
	struct TreeNode *root;
};
// Create new tree
struct BinaryTree *newTree()
{
	// Create dynamic node
	struct BinaryTree *tree = (struct BinaryTree *) malloc(sizeof(struct BinaryTree));
	if (tree != NULL)
	{
		tree->root = NULL;
	}
	else
	{
		printf("Memory Overflow to Create tree Tree\n");
	}
	//return new tree
	return tree;
}
// returns a new node of tree
struct TreeNode *newNode(int data)
{
	// Create dynamic node
	struct TreeNode *node = (struct TreeNode *) malloc(sizeof(struct TreeNode));
	if (node != NULL)
	{
		//Set data and pointer values
		node->data = data;
		node->left = NULL;
		node->right = NULL;
	}
	else
	{
		//This is indicates, segmentation fault or memory overflow problem
		printf("Memory Overflow\n");
	}
	//return new node
	return node;
}
// Swap the value of given nodes values
void swapValue(struct TreeNode *a, struct TreeNode *b)
{
	int temp = a->data;
	a->data = b->data;
	b->data = temp;
}
// Swap leaf node elements in pairwise manner
void swapLeafPair(struct TreeNode *node, struct TreeNode **prev)
{
	if (node != NULL)
	{
		if (node->left == NULL && node->right == NULL)
		{
			if ( *prev == NULL)
			{
				// First pair node
				*prev = node;
			}
			else
			{
				swapValue(node, *prev);
				// Reset pair element
				*prev = NULL;
			}
			return;
		}
		// Recursively visiting left and right subtree
		swapLeafPair(node->left, prev);
		swapLeafPair(node->right, prev);
	}
}
// Handles the request of swapping leaf nodes
void swapLeafNodes(struct TreeNode *root)
{
	if (root == NULL)
	{
		printf("\n Empty Tree \n");
		return;
	}
	struct TreeNode *prev = NULL;
	swapLeafPair(root, & prev);
}
//Display Inorder view of binary tree
void inorder(struct TreeNode *node)
{
	if (node)
	{
		inorder(node->left);
		//Print node value
		printf("  %d", node->data);
		inorder(node->right);
	}
}
int main(int argc, char
	const *argv[])
{
	struct BinaryTree *tree = newTree();
	/*
	      1
	    /  \
	   /    \
	  2      8
	 / \    / \
	3  10  6   4
	   /  / \   \
	  7  5   9   11
	            / \
	          12   13
	-----------------------
	   Binary Tree
	-----------------------
	*/
	tree->root = newNode(1);
	tree->root->left = newNode(2);
	tree->root->right = newNode(8);
	tree->root->left->left = newNode(3);
	tree->root->left->right = newNode(10);
	tree->root->left->right->left = newNode(7);
	tree->root->right->left = newNode(6);
	tree->root->right->left->right = newNode(9);
	tree->root->right->right = newNode(4);
	tree->root->right->left->left = newNode(5);
	tree->root->right->right->right = newNode(11);
	tree->root->right->right->right->left = newNode(12);
	tree->root->right->right->right->right = newNode(13);
	inorder(tree->root);
	swapLeafNodes(tree->root);
	/*
	      1
	    /  \
	   /    \
	  2      8
	 / \    / \
	7  10  6   4
	   /  / \   \
	  3  9   5   11
	            / \
	          13   12
	-----------------------
	   After swap leaf node pairs 
	-----------------------
	*/
	printf("\n After Swap Leaf nodes \n");
	inorder(tree->root);
	return 0;
}

Output

  3  2  7  10  1  5  6  9  8  4  12  11  13
 After Swap Leaf nodes
  7  2  3  10  1  9  6  5  8  4  13  11  12