[Alan Anderson]

I have three suggestions. First, notice that I forgot to declare the previous_state variable in my example. (it should be just like the current_state one).

Second, notice that I accidentally used a close brace } instead of a close parenthesis ) character after the test expression on the third if.

Third, just use what I posted as an example of how to do it, not as a complete copy-and-paste solution to your specific problem. Read it, understand it, and then write your own code.