What does ":=" refer to?

Question

I'm looking at the algorithm for breadth-first sorting of a binary search tree, and there is a symbol used that I cannot understand. Funny enough, Google returns zero results.

//  levelorder()
//      q = empty queue
//      q.enqueue(root)
//      while not q.empty do
//          node := q.dequeue()  //Referring to this
//          visit(node)
//          if node.left !=  null then
//                q.enqueue(node.left)
//          if node.right != null then
//                q.enqueue(node.right)

What is the operation being used here? I'm quite confused by this line.

Answer 1

The code you posted is pseudo code, and is not intended to be valid C++.

In C++, the assignment operator is =.

In other languages such as Ada, BCPL, Cecil, Dylan, E, Eiffel, Maple, Mathematica, Modula-3, Pascal, Pliant, Sather, Simula, Smalltalk, SML, the assignment operator is :=.
GNU make also uses := for a way of assigning.

Since the code you posted is a comment, it is not intended to be valid C++.

Here is a closer representation of the code you posted in valid C++:

#include <iostream>
#include <string>
#include <queue>  

//A node might look like this:
struct Node{
    Node* left;
    Node* right;
};

//somewhere you have a node and a root
Node* node = new Node;
Node* root = new Node;

//a visit function is called in the pseudo code you posted
void visit(Node* node){
    // ... code ...
    return;
}

//here is what valid C++ that is similar to the pseudo code:
void levelorder(){

    //empty queue
    std::queue<Node*> q;

    //add the root to the queue
    q.push(root);

    do {
        visit(node);
        if (node->left != nullptr){
            q.push(node->left);
        }
        if (node->left != nullptr){
            q.push(node->right);
        }
    }while(!q.empty());

    return;
}

//I just added this main function so the whole code snippet compiles successfully
int main(){}