private void checkUndeclaredVariable(ParseTree node) {
	
		if (node.attribute.equals("IDENTIFIER") && !containsVariable(node.value) && !undeclaredVariables.contains(node.value)) {
			System.out.println("Undeclared Variable: " + node.value);
			undeclaredVariables.add(node.value);
		}
	
		for (int i = 0; i < node.children.size(); i++)
			checkUndeclaredVariable(node.children.get(i));
	}