CODEWITHSUNDEEP
c++binary-search-treelvalue
ocean800
ocean800

Reputation: 3737

C++ - expression must be a modifiable lvalue?

So I'm implementing a BST right now and I'm trying to write a successor function. This is what I have right now: 

int BinarySearchTree::TREE_SUCCESSOR(node* x)
{

node* y = NULL;

if (x->right != NULL)
{
    return FIND_MIN(x->right);
}
else
{
    y = x->parent; 
    while (y != NULL && x = y->right)
    {
        x = y;
        y = y->parent;
    }
    return y->key; 
}
}

however on this line: 

while (y != NULL && x = y->right)

I get this error on y:

Expression must be a modifiable lvalue

Why am I getting this error?

Any help would be greatly appreciated, thanks!!

Upvotes: 1

Views: 704

Answers (1)

Vlad from Moscow
Vlad from Moscow

Reputation: 311018

It seems that you mean the following

while (y != NULL && x == y->right)
                     ^^^

As for the meaning of the error message then when you use the assignment operator then its priority is less than the priorities of equality and logical operators and you have in fact 

while ( ( y != NULL && x ) = y->right)

Take into account that it is much better to place the declaration of y in the code block of the else statement because it is used only in this scope

//...
else
{
    node* y = x->parent;

Upvotes: 6

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