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C# Intermediate C# Polymorphism Virtual Methods

Posted by McKenzie Warren
McKenzie Warren
5,698 Points

I'm just stuck on this override method...

First off, I was getting this error saying not all code paths return a value, which is why there's that random "return true;" underneath the foreach statement. But the foreach statement states that if an index of "sequence" == that index -1 (so the index immediately preceding it), it should return true, as is the prompt, right? Otherwise (else), it should return false. Does that not cover all code paths? or do I need to break out of the foreach statement as soon as it equates to true or something...?

Thanks in advance, guys!

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)
        {
            foreach (int i in sequence)
            {
                if (sequence[i] == sequence[i-1])
                {
                    return true;
                }
                else
                {
                    return false;
                }
            }
            return true;
        }
    }
}
McKenzie Warren
McKenzie Warren
5,698 Points

Thanks, Adam!!!

1 Answer

Adam McGrade
Adam McGrade
26,333 Points
Adam McGrade
Adam McGrade
26,333 Points

Inside your foreach loop, i represents the value in the at the current index in sequence rather than the index itself.

Imagine for example the sequence was [5,6,6]. In the first iteration of the loop, in your if condition, you would be testing sequence[5] == sequence[5-1].

There is no value at index 5 or at index 4 as the array only contains 3 elements ( index 0, index 1, index 2). This would result in an exception being thrown.

In this instance it makes more sense to use a for loop. This allows you to access the value at the current index sequence[index] and compare it to the next value, at sequence[index + 1].

So you would loop through each element in the sequence from the start of the sequence to the second last value of the sequence (you cant compare the last value with a value at an index that is larger than the size of the array).

If the value at the current index is equal to the value at the next index, return true because there is a match.

By default you would return false, because you only want to return true, in the instance a match is found.

        public override bool Scan(int[] sequence)
        {
             for (int i = 0; i < sequence.Length - 1; i++)
             {
                 if (sequence[i] == sequence[i+1]) 
                    return true;
             }
            return false;
       }

Hope that helps