Index outside of bounds

Question

Why is it saying my index is out of bounds? I dont know how to fix it.
```SequenceDetector.cs
namespace Treehouse.CodeChallenges
{
    class SequenceDetector
    {
        public virtual bool Scan(int[] sequence)
        {
            return true;
        }
    }
}
```
```RepeatDetector.cs
namespace Treehouse.CodeChallenges
{
    class RepeatDetector : SequenceDetector
    {
        public override bool Scan(int[] sequence)
        {
            for (int i = 0; i < sequence.Length; i++)
            {
                if (sequence[i] == sequence[i + 1])
                {
                    return true;
                }
            }
            return false;
        }
    }
}
```

Jennifer Nordell · Accepted Answer

Hi there, @Joshua Thao (https://teamtreehouse.com/joshuathao) !  I received your request for assistance. The problem here is in your for loop.  It's going just a tad too far because you also have to check what the next index is. Imagine that we have an array [3, 5, 10, 20].  The length of that would be 4. You say to check while it's less than 4 and then check the next index also. That would mean it would stop at an index of 3. The element with the index of 3 is 20. But what is the element at index + 1 (or 4)?  It's out of bounds.  To mitigate this you need to stop just one shy of the end.
So where you wrote:
```csharp
i < sequence.Length
```
That should be:
```
i < sequence.Length - 1
```
Because you still need to be able to access one more than i as well.
Hope this helps! :sparkles:

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Joshua Thao

Joshua Thao

Index outside of bounds

1 Answer

Jennifer Nordell

Jennifer Nordell