Re: do/while doesn't check condition

From:
Old Wolf <oldwolf@inspire.net.nz>
Newsgroups:
comp.lang.c++
Date:
25 Apr 2007 19:01:09 -0700
Message-ID:
<1177552868.990794.48250@n35g2000prd.googlegroups.com>
On Apr 25, 8:20 am, voger <v...@booho.com> wrote:

Hi everyone

Can anyone please explain this strange behavior?

I have this function that is supposed to copy the contents of one array to
one other array, but sorted. I don't know if the logic is correct but when
I try to debug this the do/while loop results in an endless loop.
        do
        {
           // if less than previous then swap
            if(sorted[j] < sorted[j -1])
            {
                int temp = sorted[j -1];
                sorted[j -1] = sorted[j];
                sorted[j] = temp;
                j--;
                larger = false;
            }

            // else do nothing
            else if(sorted[j] >= sorted[j -1])
            {
                larger = true;
            }
        }while(j != 0 || !larger);


Well, it is never possible to not trigger the end condition.

If the first block is selected, then 'larger' is false so the loop
continues. If the second block is selected then j can't have
been zero, so the loop continues. If neither block is selected
then 'j' and 'larger' have the same values as they had on the
previous iteration, which continued, so the current one must
also continue.

Try writing your logic out as a flow-chart first, and then check
if your code corresponds to it or not.

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