I can't understand exactly what you want to do. This sample code merely pass the address of arr to fibo. Note: the last time I did C was more than 20...
DS is correct using a select object does not work very easily and checkboxes are called for. Also trying to get a listener working seemed hard if not...
This is a situation where I'd be using checkboxes, NOT a SELECT (what I assume you mean by 'dropdown' which is technically the incorrect term). Then...