BinarySearch.cs

// Needs the array to already be SORTED!
static int BinarySearch(int[] items, int itemToSearch)
{
    // Create a variable to store the lower boundary
    int start = 0,
    // Create a variable to store the upper boundary
        end = items.Length - 1,
    // Create a variable to store the middle of the boundary
        mid = (start + end) / 2;
    // Create a variable to determine whether the item is
    // actually found
    bool found = false;

    // Carry on looping while the lower bound is smaller than
    // the upper bound and the value is still not found
    while (start <= end && !found)
    {
        // Check is the value is in the upper half of the array
        if (items[mid] < itemToSearch)
        {
            // If it is, set the lower bound to the middle value
            // + 1
            start = mid + 1;
            // Recalculate the mid value
            mid = (start + end) / 2;
        }
        // Check if the value is in the lower half of the array
        else if (itemToSearch < items[mid])
        {
            // If it is, set the upper bound to the middle value
            // - 1
            end = mid - 1;
            // Recalculate the mid value
            mid = (start + end) / 2;
        }
        // Check if the mid value matches our desired value
        else if (items[mid] == itemToSearch)
        {
            // If it does, set the boolean to true so we can exit
            // the loop
            found = true;
        }
    }

    // Check if the array exited because the start boundary became
    // larger than the end boundary or whether the item was actually
    // found
    if (found)
        // If the item was found, return its position
        return mid;
    else
        // Else return -1 for NOT FOUND
        return -1;
}