swap max and min in tree

void punktD(treeNode* root)
{
    int min, max;
    stackNode* top;
    treeNode* marker;
    treeNode* minn;
    treeNode* maxx;
    marker = root;
    minn = root;
    maxx = root;
    min = marker->data;
    max = marker->data;
    top = NULL;
    if (root != NULL)
        push_stack(top, root);
    while (top != NULL)
    {
        pop_stack(top, marker);
        while (marker != NULL)
        {
            if (marker->data < min)
            {
                min = marker->data;
                minn = marker;
            }
            if (marker->data > max)
            {
                max = marker->data;
                maxx = marker;
            }
            if (marker->right != NULL)
                push_stack(top, marker->right);
            marker = marker->left;
        }
    }
    swap(minn->data, maxx->data);
}