On 16/10/21 18:41, David G. Johnston wrote:
On Friday, October 15, 2021, Ron <ronljohnsonjr@xxxxxxxxx> wrote:
Prima facie, if you were told "numbers in the range 0-10", would
you really think, "ah, they *really* mean 0 through 9"?
I would indeed default to both endpoints of the range being
inclusive. I also begin counting at one, not zero. I’ve long gotten
past being surprised when computer science and my defaults don’t
agree. Choices are made and documented and that works for me.
As for this, documentation I never really gave the wording a second
thought before, though I can definitely understand the complaint and
like the somewhat wordier, but less linguistically challenging,
phrasing the OP suggested (Boundary point, especially by itself, is
not an improvement).
David J.
The reason arrays generally start at zero and not one, is efficiency.
When indexes are zero based then the displacement in bytes from the
start address of x[n] is simply:
startAddress + n * sizeOfElement
If the start of an array had the index of one, then you have subtract
one each time, so the displacement from the start address of x[n] now
becomes
startAddress + (n - 1) * sizeOfElement
Half open intervals make life a lot simpler so it is the natural
default, to prevent intervals from having any numbers in common.
If you have 3 intervals spanning the range [0, 30), and you are only
dealing with integers then you can split the range as:
[0, 9] 0 <= x <= 9
[10, 19] 10 <= x <= 19
[20, 29] 10 <= x <= 29
But what if you are dealing with floats? The above arrangement would not
work, as 9.78 would not be in any interval, so you need half open
intervals, such as:
[0, 10) 0 <= x < 10
[10, 20) 10 <= x < 20
[20, 30) 10 <= x < 30
So you know what number each interval starts at, and every number in the
range is covered.
-Gavin
