Loop iterator offset

Question

Let's say I've an array of 4 items.

When I access the first index, I would also like to access an offset of -1 (in this case, it would loop to 3)

for(int i = 0; i < array.Length; i++)
{
  int item = array[i];

  int offset = 0;
  if (i == 0)
  {
    offset = array.Length -1;
  }
  else 
  {
    offset = i -1;
  }
  int offsetItem = array[offset];
}

Is there a more elegant way of achieving this? I keep thinking of using the modulo operator, but I don't understand it well enough to know if its the solution.

Answer 1

Yes, there is. Add the length of the array to the index, and use remainder operator, like this:

int offset = (i-1+array.Length) % array.Length;

Answer 2

you cannot define variable i within the loop as i has already been defined.

  for(int i = 0; i < array.Length; i++) {
           int j = array[i];  
           int offset = (j == 0)?(array.Length -1):( i -1);    
           int offsetItem = array[offset];
  }