Get previous/next item of a given item in a List<>

Question

Says I have this List : 1, 3, 5, 7, 9, 13

For example, given value is : 9, the previous item is 7 and the next item is 13

How can I achieve this using C#?

Answer 1

int index = list.IndexOf(9); // find the index of the given number

// find the index of next and the previous number
// by taking into account that 
// the given number might be the first or the last number in the list
int prev = index > 0 ? index - 1 : -1;

int next = index < list.Count - 1 ? index + 1 : -1;

int nextItem, prevItem;

// if indexes are valid then get the items using indexer 
// otherwise set them to a temporary value, 
// you can also use Nullable instead
nextItem = prev != -1 ? list[prev] : 0;
prevItem = next != -1 ? list[next] : 0;