C# Loop Array Index Values back to Beginning of Array once out of Index

Question

I am looking to create a program like the following (c# btw):

int[] arr = new int[9]
//some code that puts values 1, 0, or 2 in each array element
for(int i = 0; i < arr.Length; i++)
{
    if (arr[i] == arr[i + 3]) { return true; }
}

So, for each value in the array I am applying a formula that does something with that value and the value 3 indexes ahead of it. Of course, this runs into an out of range exception once i+3>8.

What I'd like to do is if the the desired index is out of range then loop the index values back around to the beginning of the array. So, in an array of length 9 where the last index is 8, if on a given loop i = 7, and i+3 then = 10, I would like i+3 to 'become,' by whatever means, 1, and then when i = 8, and i+3 = 11, I want i+3 to become 2.

So, the index pairs being evaluated would be something like:

i , i+3

0 3

1 4

2 5

3 6

4 7

5 8

6 0

7 1

8 2

how can I go about doing this?

Thanks for any help.

What have you tried doing? Have you already learned about the % operator? What is the problem? — UnholySheep
– UnholySheep, Commented Apr 9, 2017 at 16:34

Lucero · Accepted Answer · 2017-04-09 16:34:38Z

4

Use the modulo operator like this:

if (arr[i] == arr[(i + 3) % arr.Length]) { return true; }

answered Apr 9, 2017 at 16:34

Lucero

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1 Comment

bababaram Over a year ago

Thanks! I was afraid that this would be difficult/impossible to implement!

Christos · Accepted Answer · 2017-04-09 17:10:22Z

3

You could try the following expression inside your if statement.

arr[i] == arr[(i + 3) % arr.Length];

The % Operator

Divides the value of one expression by the value of another, and returns the remainder.

edited Apr 9, 2017 at 17:10

answered Apr 9, 2017 at 16:35

Christos

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2 Comments

Christos Over a year ago

@Johnbot My bad...Thanks, I corrected the link. However, regarding the name, I don't think is wrong we call it Modulus operator. You will find with a bit googling this term also be used as the term remainder operator.

Johnbot Over a year ago

This answer shows the difference between the two and is also applicable to C#.

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