Is it possible to increment arrays?

I've been learning VB at college, for one of my assignments and for one task I seem to have overshot my ability somewhat. I have been able to solve all of the problems I have encounters thus-far however this one is too much for me to figure out, and I can't seem to find a solution on Google either.

The program is an application for waiters to take orders easily, the problem arises when more than one pizza needs to be ordered.

        If rdobtnCola.Checked Then
            Class1.arrDrink(0) = "Cola"
            Class1.varCost = Class1.varCost + 0.9
            Class1.varCurrentCost = Class1.varCurrentCost + 0.9

I need a way to incrament
Class1.arrDrink(0) up to
Class1.arrDrink(1)

Is this possible?