Starting a For loop at (-1)

[joatmon]

Is there any reason that I can't start a For loop at (-1), rather than the usual choices of 0 or 1 (or any other positive integer)? I'm not getting an error message, but I am getting weird results when using the index as an array reference. I'm not going out of bounds or anything. The index is just used as an offset, so I know that I am within bounds.

This is a project where we have to speed up code as fast as possible, so I'm trying to get as much math out of the inner loop as I can. By starting the loop at -1, I don't have to subtract 1 with each array reference in the loop.

Here is some code:

for (int i = (-1); i < 2; i++) {
  val0 = val0 + myArray[row + i];
  val1 = val1 + myArray[row + i];
  val2 = val2 + myArray[row + i];
}

[ResidentBiscuit]

I don't see why you don't just start i at 0. And what is row?

[firedraco]

That looks fine to me. I'm guessing you actually ARE going out of bounds there if you are getting weird errors like that...recheck your code to make sure.

[joatmon]

Thanks!