A question

Well, its another project from me. This is a confusing one for me at least. They ask us to make a program that acts like a cell phone text message. The user is asked to input the numbers and they will test it when the numbers are separated by spaces and it creates a character whenever a -1 appears. For example, 2 -1 = 'a', 2 2 -1 = 'b', 2 2 2 = 'c', and so on and so on. This one has me stumped about it because I'm not sure how to write the input as for spaces and then to count how many of the #'s come before the -1. Thanks for any help.

P.S. I'm fairly new at this so don't go too far advanced or I won't understand it. I was given a hint to use while loops and possible to use nesting while loops. All I need is something that I can understand to start on, just so it's not given to me. Gotta learn somehow, huh? Thanks.