Infinitely loops an array in both directions while respecting the array bounds

loop_array_both_directions.cs

using System;
					
public class Program
{
	public static void Main()
	{
		var index = 0;
		var arr = new int[] { 1, 2, 3, 4 };
		
		for(int i = 0; i < 20; i++) {
			if(i < 10)
				index++;
			else
				index--;
			
			index = (index + arr.Length)%arr.Length;
		
			Console.WriteLine("index: " + index + ", " + arr[index] + " (" + (i < 10 ? "forward" : "backward") + ")");		
		}		
	}
}

This line is useful when you have a gallery of images (for example) with navigation arrows that you want to infinitely scroll through:

index = (index + arr.Length)%arr.Length;

This saves you unnecessary if branching and bounds checks...

Output:

index: 1, 2 (forward)
index: 2, 3 (forward)
index: 3, 4 (forward)
index: 0, 1 (forward)
index: 1, 2 (forward)
index: 2, 3 (forward)
index: 3, 4 (forward)
index: 0, 1 (forward)
index: 1, 2 (forward)
index: 2, 3 (forward)
index: 1, 2 (backward)
index: 0, 1 (backward)
index: 3, 4 (backward)
index: 2, 3 (backward)
index: 1, 2 (backward)
index: 0, 1 (backward)
index: 3, 4 (backward)
index: 2, 3 (backward)
index: 1, 2 (backward)
index: 0, 1 (backward)