CODEWITHSUNDEEP
c++
Johnny Cherries
Johnny Cherries

Reputation: 35

What is the meaning of the "<" operator?

In the following code for a binary search tree:

template <class TKey>
class bst<TKey>::node *bst<TKey>::insert(node *T, TKey &key)
{
  if (T == NULL) {
    T = new node;
    T->key = key;
  } else if (T->key == key) {
    cout << "key " << key << " already in tree" << endl;
  } else {
    
    int dir = T->key < key;
    T->link[dir] = insert(T->link[dir], key);   
  }
  return T;
}

I'm confused what the line

int dir = T->key < key;

is doing. I could understand int dir = T->key, although of course that wouldn't make sense, but I've not seen the < operator used in that way before. Any clues?

Upvotes: 3

Views: 10020

Answers (5)

Nikos C.
Nikos C.

Reputation: 51832

If the operator isn't overloaded, than it has the usual meaning; it evaluates to either true or false. This is a bool type, and therefore can be implicitly converted to an int.

However, if TKey is a class and overloads it, or there's a global overload, then we've no idea what it does unless we see the code.

Upvotes: 6

Steve Robinson
Steve Robinson

Reputation: 3939

Well, as the binary search tree stores values lesser than root on left and greater values on right, you need select which direction the insertion is gonna take place. To do this you are comparing the key with the current node's value. The result of this comparison is stored in dir variable. So if key is lesser than T's value, dir gets 1 which represents left side in the link[] that holds pointers to the left and right branches of the node T. And then insertion is done recursively with the left node of T. That is why you do a comparison there. Just to see whether we must insert the element to the right or left of the current node.

Upvotes: 0

Patrick White
Patrick White

Reputation: 681

The < operator is a boolean comparison operator - i.e. it evaluates to 0 if the condition is false, and 1 if the condition is true. It's usually used in conditionals, but using the return value directly is perfectly valid. In this case, if the value of T->key is less than the value of key, dir will be 1 otherwise dir will be 0.

Upvotes: 0

jonvuri
jonvuri

Reputation: 5920

< returns 1 if the first operand is less than the second operand, or 0 otherwise.

Upvotes: 0

user93353
user93353

Reputation: 14039

T->key < key is a condition. It will evaluate to either true or false. If it evaluates to true, dir will get value 1, otherwise it will get value 0.

int dir = T->key < key;

is short form for writing

int dir;
if(T->key < key)
    dir = 1;
else
    dir = 0;

When a boolean is assigned to an int, it gets the value 0 or 1 corresponding to false or true.

Upvotes: 9

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