HELP - getting the message: bummer, index was outside the bounds of the array message on course objective

In your if statement conditions

sequence[i] > 0 && sequence[i] == sequence[i - 1]

You access sequence[i-1] since i starts at 0 your code will try to access sequence[-1] on it's first run which is an invalid index. Also while it doesn't cause a direct issue with the task I'm not quite sure what the logic behind your first condition is. It's not something that has to be there to complete the objective.

It's also worth mentioning that you were actually meant to place the RepeatDetector class is a separate file from the SequenceDetector class, but doing so is not actually mandatory to complete the challenge.

If you start i at 1 rather than 0 and remove your first condition like this:

namespace Treehouse.CodeChallenges
{
    class SequenceDetector
    {
        public virtual bool Scan(int[] sequence)
        {
            return true;
        }
    }
    class RepeatDetector : SequenceDetector{
        public override bool Scan(int[] sequence) {
            for(int i = 1; i < sequence.Length; i++) {
                if(sequence[i] == sequence[i - 1]) {
                    return true;
                }
            }
            return false;
        }
    }
}

Then your code will pass the challenge.

You and me both. :)

I think you're getting the error because you're doing a i - 1 in the loop. When the loop starts i will be 0, so it's going to try to get sequence[-1] which doesn't exist.

Here's a trick I used for when I did the challenge:

• Try using a foreach instead. I always find that to be so much easier to read than having to deal with indexes of the array.