PHP: Simple recursive function into iterative function

Question

I was going to do it in C but was confused, so I turned to PHP and was able to copy a recursive function to do this. I am converting an integer into a string with math. Here it is:

function intToString($myDecimal){
    if($myDecimal < 10) {
        return $myDecimal;
    }
    return intToString(($myDecimal / 10)) . ($myDecimal % 10);
}

I was able to convert a recursive factorial function before.. but with this I just have no clue.. My attempt is as follows:

function intToStringIter($myDecimal){
    $out = "";
    while($myDecimal > 10) {
        $myDecimal /= 10;
        $out .= $myDecimal;
    }
    $out .= $myDecimal % 10;
    return $out;
}

I think I am too tired to see the proper logic at the moment.. It returns 22 instead of 20, I cannot wrap my head around what is correct. Do you see what I am doing wrong?

I can't find the point. Is this homework? Conversion between integer and strings isn't needed in PHP. — xPheRe
– xPheRe, Commented Nov 5, 2010 at 9:48
@xPheRe, It was for an interview question a friend had asked about, he wasn't in the interview he just read about the question, I was helping him understand how to do it. — John
– John, Commented Nov 5, 2010 at 19:07

xPheRe · Accepted Answer · 2010-11-05 10:01:06Z

1

If you're looking for a conversion to string for big unsigned integers, the code is actually:

function intToString($myDecimal)
{
    return sprintf('%u', $myDecimal);
}

If you need to do it with iteration:

function intToString($myDecimal)
{
    $result = '';
    while ($myDecimal > 9) {
        $result = ($myDecimal % 10) . $result;
        $myDecimal /= 10;
    }
    return $myDecimal . $result;
}

UPDATE: My bad, digits were inserted in reversed order. Now it should work. Sorry, untested too.

edited Nov 5, 2010 at 10:01

answered Nov 5, 2010 at 9:52

xPheRe

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3 Comments

John Over a year ago

I was wanting to do it in C, which used no standard functions (so sprintf is out), your second example spits out "02" instead of "20", weird. I am really just helping somebody do this in C, I will stop wracking my mind and go to sleep. :)

xPheRe Over a year ago

I updated my answer, you were right, it built the string in reverse order. Now it should work fine. I hope.

John Over a year ago

Ah! After some sleep I understand this now, it works perfectly and applies to the problem I wanted to help somebody with. It should be simple to do in C now (with simple ASCII addition). Thank you

Lekensteyn · Accepted Answer · 2010-11-05 09:52:50Z

0

PHP is not very strict with variables. An integer will become an float if the situation likes it. In your code, $myDecimal /= 10 could make a float of $myDecimal. The following forces $myDecimal to stay an integer. Note: you should pass only integers, if you're passing 9.99, the output would still be 9.99 because 9.99 < 10.

function intToStringIter($myDecimal){
    $out = "";
    while($myDecimal >= 10) {
        $myDecimal = (int) ($myDecimal / 10);
        $out .= $myDecimal;
    }
    $out .= $myDecimal % 10;
    return $out;
}

answered Nov 5, 2010 at 9:52

Lekensteyn

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