-1 #Ind Question

I am currently writing a c++ for binary trees. The whole thing is written, however, no matter what expression I want to evaluate, I keep having the command prompt tell me -1.#IND. Any ideas on a fix for this or even what this means?

Thanks in advance

Code:

#include <iostream>
#include <string>
#include <cctype>
using namespace std;
template<typename T> struct TreeNode
{
    TreeNode(const T& value, TreeNode<T>* left = NULL, TreeNode<T>* right = NULL)
    {
        Value = value;
        Left = left;
        Right = right;
    }

    T Value;
    TreeNode<T>* Left;
    TreeNode<T>* Right;

    bool IsLeaf() const
    {
        return Left == NULL && Right == NULL;
    }
};


double ValueOf(TreeNode<char>* treeNode)
{


    if ( treeNode->IsLeaf() )
    {
        return treeNode->Value - '0';
    }
    else
    {
        switch(treeNode->Value)
        {
        case '+':
            return ValueOf(treeNode->Left) + ValueOf(treeNode->Right);
            break;

        case '-':
            return ValueOf(treeNode->Left) - ValueOf(treeNode->Right);
            break;

        case '*':
            return ValueOf(treeNode->Left) * ValueOf(treeNode->Right);
            break;

        case '/':
            return ValueOf(treeNode->Left) / ValueOf(treeNode->Right);
            break;
        }


    }
}



void main()
{
    string expression;

    cout << "Please enter an expression: ";

    cin >> expression;


    TreeNode<char> *newLeaf;
    TreeNode<char> *treeRoot;
    TreeNode<char> *currentNode;
    TreeNode<char> *newRoot;
    TreeNode<char> *newChild;


    treeRoot = NULL;
    currentNode = treeRoot;


    for (int i = 0; i < expression.length(); i++)
    {

        if ( (expression[i] >= 0 ) || ( expression[i] <= 9 ) ) 
        {

            newLeaf = new TreeNode <char> (expression[i]);


            if ( currentNode == NULL)
            {
                treeRoot = currentNode = newLeaf;
            }
            else
            {
                currentNode->Right = newLeaf;
            }
        }

        else if ( (( expression[i] == '+' || expression[i] == '-') || (expression[i] == '*' || expression[i] == '/' )) && currentNode->Right == NULL ) 
        {
            newRoot = new TreeNode <char> (expression[i]);
            newRoot->Left = treeRoot;
            treeRoot = newRoot;
            currentNode = newRoot;
        }

        else if (expression[i] == '*' || expression[i] == '/')
        {
            newChild = new TreeNode <char> (expression[i]);
            newChild->Left = currentNode->Right;
            currentNode->Right = newChild;
            currentNode = newChild;
        }
    } 

    double result = ValueOf(treeRoot);
    cout << "The result is: " << result << endl;
    system("pause");
}