Subj : Re: Reversing a number
To   : comp.programming
From : Roger Willcocks
Date : Sun Sep 11 2005 11:22 pm

"Irrwahn Grausewitz" <irrwahn35@freenet.de> wrote in message 
news:shv7i1p3on0qpsr2rumeifst69o8tjtp32@4ax.com...
> zeroxia@gmail.com wrote:
>>Is this implementation not compiler-specific?
>>(For example, the case of which i is negative.
>
> That's not a problem, if you don't mind that the result
> will be negative, too.
>
>>int reverse(int i)
>>{
>>    int n = (i % 10);
>>    i /= 10;
>
> But why treat the first iteration as a special case?
> Just replace the two lines above with:
>
>     int n = 0;
>
>>    while (i)
>>    {
>>        n *= 10;
>>        n += i % 10;
>>        i /= 10;
>>    }
>>    return n;
>>}

Then reverse(10000) is (1).

Consider the normal recursive method of printing a number:

printnumber(int number)
{
    if (number >= 10) /* any leading digits? */
        printnumber(number / 10); /* print them first */
    print(number % 10); /* print the trailing digit */
}

and think what happens if you print the rightmost digit before printing the 
other digits:

printnumber(int number)
{
    print(number % 10);
    if (number >= 10)
        printnumber(number / 10);
}

--
Roger

.