C++ binary tree /entropy

#include <conio.h>
#include <iostream>
#include <cctype>
#include <string>
#include <fstream>
#include <math.h>
    using namespace std;

#define MAX_LEN_FILE    256
#define M_LOG2E 1.44269504088896340736 //log2(e)

inline long double log2(const long double x){
    return  log(x) * M_LOG2E;
}

struct TreeNode
{
    string word;
    int grade, count;
    TreeNode *left;
    TreeNode *right;

    TreeNode(string str, int g)
    {
        word = str;
        grade = g;
        count = 1;
        left = NULL;
        right = NULL;
    }
};

void Find(TreeNode *node, string str, int g)
{
    if (g == node->grade)
    {
        if (str == node->word)
        {
            // Yes, the item has been found in the root node.
            node->count++;
            return;
        }
    }
    else if (g < node->grade) {
        // If the item occurs, it must be in the left subtree.
        if (node->left == NULL)
        {
            node->left = new TreeNode(str, g);
            return;
        }
        else
            return Find( node->left, str, g );
    }
    else {
        // If the item occurs, it must be in the right subtree.
        if (node->right == NULL)
        {
            node->right = new TreeNode(str, g);
            return;
        }
        else
        return Find( node->right, str, g );
    }
}

double ComputeEntropy(TreeNode *root, int count)
{
    double entropy = 0;

    entropy += (-log2(root->count/(double)count)) * root->count;

    if (root->left != NULL)
        entropy += ComputeEntropy(root->left, count);

    if (root->right != NULL)
        entropy += ComputeEntropy(root->right, count);

    return entropy;
}

int main()
{
    TreeNode *root;
    char name[MAX_LEN_FILE], temp;
    bool first = true;
    int wordsCount = 0;

    root = NULL;

    cout << "Zadejte cestu k souboru: ";
    cin >> name;

    ifstream file;

    file.open (name, ifstream::in);

    if(!file.is_open())
    {
        cout << "Spatne zadana cesta k souboru!" << endl;
        getche();
        return 0;
    }

    int grade = 0;
    string word;

    while (file.get(temp) && !file.eof())
    {

        if(isalpha(temp))
        {
            word += temp;
            grade += temp;
        }
        else if (word != "")
        {
            if (first)
            {
                root = new TreeNode(word, grade);
                first = false;
            }
            else
            {
                Find(root, word, grade);
            }

            wordsCount++;
            grade = 0;
            word = "";
        }
    }

    file.close();

    cout.precision(10); // ??
    cout << fixed << ComputeEntropy(root, wordsCount);

    getche();
    return 0;
}