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C# Intermediate C# Polymorphism Virtual Methods

drstrangequark
drstrangequark
8,273 Points
Posted by drstrangequark
drstrangequark
8,273 Points

How do I reference the previous value in an array?

The challenge asks me to return true if any value in the array is the same as the preceding value. However, I've looked online and can't find out how to reference the immediately preceding value. I know the code I have written is incorrect but I'm not sure what to do here.

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)
        {
            if(sequence[this] = sequence[this - 1])
            {
                return true;
            }
        }
    }
}

2 Answers

Allan Clark
Allan Clark
10,810 Points
Allan Clark
Allan Clark
10,810 Points

I would use a for loop, and just out of preference i would check it the other way around (if the index is the same as the next index). The loop can look something like this:

for(int idx = 0; i < sequence.Length - 1; i++){ //I do Length - 1 here to avoid off by one error, because the last item has 
        if(sequence[idx] == sequence[idx + 1]) //nothing to compare to.
                return true;
}

and if it gets all the way through the loop that means there was no match so just return false.

drstrangequark
drstrangequark
8,273 Points
drstrangequark
drstrangequark
8,273 Points

I gave the for loop a try and it returned this error:

RepeatDetector.cs(5,30): error CS0161: `Treehouse.CodeChallenges.RepeatDetector.Scan(int[])': not all code paths return a value Compilation failed: 1 error(s), 0 warnings

Allan Clark
Allan Clark
10,810 Points
Allan Clark
Allan Clark
10,810 Points

You need to return something when the for loop completes without hitting the return. So just add this after the loop.

return false;
Alexander La Bianca
Alexander La Bianca
15,959 Points

You could modify it a bit to not get that error by doing:

boolean flag = false;
for(int idx = 0; i < sequence.Length - 1; i++){ //I do Length - 1 here to avoid off by one error, because the last item has 
        if(sequence[idx] == sequence[idx + 1]) //nothing to compare to.
                flag = true;

}
return flag;

That way all code paths lead to a return value of true or false

drstrangequark
drstrangequark
8,273 Points
drstrangequark
drstrangequark
8,273 Points

Yup, that did it. Thanks guys.