C# sorting arrays in ascending and descending order

Question

I\'m having trouble writing a method that returns true if the elements of an array (numbers) are in sorted order, ascending or descending, and false, if they are not in any

Answer 1

This uses one loop to test both cases:

public static bool IsSorted<T>(IEnumerable<T> items, Comparer<T> comparer = null)
{
    if (items == null) throw new ArgumentNullException("items");
    if (!items.Skip(1).Any()) return true;  // only one item

    if (comparer == null) comparer = Comparer<T>.Default;
    bool ascendingOrder = true; bool descendingOrder = true;

    T last = items.First();
    foreach (T current in items.Skip(1))
    {
        int diff = comparer.Compare(last, current);
        if (diff > 0)
        {
            ascendingOrder = false;
        }
        if (diff < 0)
        {
            descendingOrder = false;
        }
        last = current;
        if(!ascendingOrder && !descendingOrder) return false;
    }
    return (ascendingOrder || descendingOrder);
}

usage:

int[] ints = { 1, 2, 3, 4, 5, 6 };
bool isOrderedAsc = IsSorted(ints); // true
bool isOrderedDesc = IsSorted(ints.Reverse()); //true

If you make it an extension method you can use it with any type:

bool ordered = new[]{"A", "B", "C"}.IsSorted();