How to write arrays & loops to display the span of stocks

For my assignment, I need 5 text boxes for entering 5 stock prices (which I have)
I added a "SHow Span" button but I do not know how to write array and loops to display in the last textbox to display the span (like[1, 1, 2, 1, 4, 5,]).
I was given some hints with the codes but I do not know how to work them.  

I have this so far