BinarySearch.cs

// Iterative
static int BinarySearch(int[] arr, int value)
{
    int left = 0;
    int right = arr.Length - 1;

    while (left <= right)
    {
        int mid = left + (right - left) / 2;

        if (arr[mid] == value)
        {
            return mid;
        }
        else if (value > arr[mid])
        {
            left = mid + 1;
        }
        else
        {
            right = mid - 1;
        }

    }

    return -1;
}

// Recursive
 static int BinarySearch(int[] arr, int left, int right, int value)
{
    if (left <= right)
    {
        int mid = left + (right - left) / 2;

        if (arr[mid] == value)
        {
            return mid;
        }
        else if (value > arr[mid])
        {
            return BinarySearch(arr, mid + 1, right, value);
        }
        else
        {
            return BinarySearch(arr, left, mid - 1, value);
        }
    }

    return -1;
}