i is probably an integer, 1 is a constant, V[i-1] says, "Fetch type of V array at the location V with offset i - 1". Example:
Let i equal 4.
This says V[4-1] which is the same as saying V. The number in the brackets indicates the element to fetch in the array. I can't tell you why they subtracted 1 and/or compared it to 25 without looking at more code (if the code has any use at all).