security digit program
<p>I need the code for this problem:</p>

<p>All the non-zero digits in the number are multiplied by each other. All the non-zero digits of the resulting number are again multiplied by each other - and so on until a single digit is left. That is the security digit.</p>

<p>Write a program that will provide the security digit for any number with up to 20 digits.</p>
