Question

Here’s my code:

  template <typename DataType> bool SearchValue(TreeNode<DataType> *root, DataType search_value)
{
    if(search_value != root->data)
    {
        if(root->right != NULL)
        {
            return SearchValue(root->right, search_value);
        }
        if (root->left != NULL)
        {
            return SearchValue(root->left, search_value);
        }
        return false;
    }
    else
    {
        return true;
    }
}

I can’t make SearchValue function work properly. The condition is not to change the signature of SearchValue function.
The problem is following: for example we try to find the element with data field equals “90” and it exists in the tree. Sometimes this code finds this element and sometimes not – depending on it’s position in the tree.
The question is how to make it work right every time.

I build the tree in such way:

template <typename DataType> TreeNode<DataType> *BuildTree()
{
    TreeNode<DataType> *root = new TreeNode<DataType>(10, new TreeNode<DataType>(20), new TreeNode<DataType>(30));

    TreeNode<DataType> *curRoot = root;
    curRoot = curRoot->left;
    curRoot->left = new TreeNode<DataType>(40);
    curRoot->left->left = new TreeNode<DataType>(70);
    curRoot->right = new TreeNode<DataType>(50);
    curRoot = curRoot->right;
    curRoot->left = new TreeNode<DataType>(80, new TreeNode<DataType>(100), new TreeNode<DataType>(110));
    curRoot = root->right;
    curRoot->left = new TreeNode<DataType>(60);
    curRoot = curRoot->left;
    curRoot->right = new TreeNode<DataType>(90, new TreeNode<DataType>(120), new TreeNode<DataType>(130));

    return root;
}

I test the search this way:

TreeNode<int> *treeRoot = BuildTree<int>();
    int valueToFind = treeRoot->data;
    cout << "Enter the value you'd like to find in the tree: ";
    cin >> valueToFind;
    cin.get();
    if(SearchValue(treeRoot, valueToFind) == true)
    {
        cout << "Value " << valueToFind << " was found!";
    }

The way I implement the tree:

template <typename DataType> struct TreeNode
{
    TreeNode(DataType val, TreeNode<DataType> *leftPtr = NULL, TreeNode<DataType> *rightPtr = NULL)
    {
        left = leftPtr;
        right = rightPtr;
        data = val;
    }
    TreeNode<DataType> *left, *right;
    DataType data;
};

Answer 1

Change

if(root->right != NULL)
{
    return SearchValue(root->right, search_value);
}
if (root->left != NULL)
{
    return SearchValue(root->left, search_value);
}
return false;

to

if(root->right != NULL)
{
    if (SearchValue(root->right, search_value))
        return true;
}
if (root->left != NULL)
{
    if (SearchValue(root->left, search_value))
        return true;
}
return false;

The way you currently have it, it will always go down the right branch and return if it was found there, never checking the left branch.