Unhandled exception at 0x012351CF in HW3.exe: 0xC0000005: Access violation reading location 0x00000004

I have done an implementation of a (ADT) binary shearch tree, i had to do a function which count the number of Parents that thire sons have a difference which is less then five. the program works, only this functon fails.

at the 'return' (recursive) i got a break point.

int difference(BSTNode *root, comperFunc cmpFn, comperFunc lesserThenFive)
{
    int count = 0;
    if (root)
    {
        count = 0;
        if (root->Left && root->Right)
        {
            //if root->Right > root->Left
            if (cmpFn(root->Right->key, root->Left->key) == 1)
            {
                if (lesserThenFive(root->Right->key, root->Left->key))
                     count = 1;  
            }
            //if root->Right < root->Left
            if (cmpFn(root->Right->key, root->Left->key) == -1)
            {
                if (lesserThenFive(root->Left->key, root->Right->key))
                    count = 1;    
            }
       }
   }
   return difference(root->Left, cmpFn, lesserThenFive) + difference(root- >Right, cmpFn, lesserThenFive) + count;//here is the break point

}

In your return statement you will dereference a null pointer, if you enter difference and root is null.

That return needs to be inside the if bock and you need to return some sutable value in the else part.

To expand a bit. Your algorithm recursivley calls difference with the left and right nodes of the current root but eventually one of root->left or root->right is going to be NULL. Your return statement will then, effectively try to call difference with the left or right member of NULL e.g. NULL->left. This will seg fault on any modern operating system.