In main, you declare a list of strings called prefix

queue_type<string> prefix;

for(string s; s!="#"; )
{
	cin >> s;
	if(s != "#")
		prefix.inserttail(s);
}

bexprtree x;
x.buildtree(prefix);
cout << x.evaluate();  // make this more user friendly

buildtree (note the name change):
newprefix = prefix;	// not necessary if prefix is passed by value
							// instead of const reference
							/ if you understand what this means, make the change
builder (root, newprefix);

builder:
	if (prefix.size() > 0)
	{
	   prefix.retrieve (item, 1);
	   prefix.delete (1);
	   root = new bnode<type>;
	   root->item = item;
		if item is an operator  // note this is not c++ code
	   {
	         build (root->left->root, prefix);
	         build (root->right->root, prefix);
		}
	}

Evaluate:
return evaluator(root);

evaluator:
	if (root != 0)
	{
		item = root->item;
		if item is an operator
		{
				leftvalue  = evaluator(root -> left->root);
				rightvalue  = evaluator(root -> right->root);
			/* The following comment should be translated to c++ code
			depending on the value of the item
				'+': return leftvalue + rightvalue

				'-': return leftvalue - rightvalue

			 '*': return leftvalue * rightvalue

				'/': return leftvalue / rightvalue
			 */
	   }
	   else
	   {
			return double(item);
		}
	}