How to remove division by zero from this function?

Question

I use this php function to convert a numeric timestamp to something like "7 days ago", but a certain timestamp returns division by zero error, I don't know how to fix the function.

function timestamp_to_ago($timestamp){
    if(isset($timestamp) and $timestamp !=''){  
        $difference = time() - $timestamp;
        $periods = array("second", "minute", "hour", "day", "week", "month", "year", "decade");
        $lengths = array("60","60","24","7","4.35","12","10");
        for($j = 0; $difference >= $lengths[$j]; $j++){
            $difference /= $lengths[$j]; // <<< line with problem
        }
        $difference = round($difference);
        if($difference != 1) $periods[$j].= "s";
        $text = "$difference $periods[$j] ago";
        return $text;
    }
}

// returns division by zero error
echo timestamp_to_ago(1135288800);

// doesn't return division by zero
echo timestamp_to_ago(1235288800);

The division by zero is triggered at this line $difference /= $lengths[$j]; but I don't know how to fix the function to avoid this error.

Maybe you can check for `$lengths[$j]` value and perform the division operation only when it has a non-zero value ? — Maximus2012, Jan 04 '16 at 23:00

score 3 · Accepted Answer · answered Jan 04 '16 at 23:00

3

What happens, if it is more than a decade old?

    for($j = 0; isset($lengths[$j]) && $difference >= $lengths[$j]; $j++){
        $difference /= $lengths[$j]; // <<< line with problem
    }

answered Jan 04 '16 at 23:00

Gennadiy Litvinyuk

1,536
12
21

score 1 · Answer 2 · answered Jan 04 '16 at 23:06

The problem is that your loop doesn't stop when it reaches the end of $lengths. When $i reaches the length of the array, $lengths[$i] is undefined, and that gets converted to 0 when dividing.

You can use foreach instead of for.

foreach ($lengths as $j => $length) {
    if ($difference < $length) {
        break;
    }
    $difference /= $length;
}
$period = $periods[$j];

Jab · Answer 3 · 2016-01-04T23:57:17.673

It seems as though these arrays are static and establish a baseline for your result. If so you are missing a value for "second". You either need to add a value in lengths or remove "seconds" from periods to fix this divide by zero error. I believe (after reading your question that below is what you are trying to achieve though because it seems the logic is flawed.

function timestamp_to_ago($timestamp){
    if(isset($timestamp) and $timestamp !=''){  
        $difference = time() - $timestamp;
        $periods = array("second", "minute", "hour", "day", "week", "month", "year", "decade");
        $lengths = array("60","60","24","7","4.35","12","10");
        for($j = 1; $difference >= $lengths[$j-1]; $j++){
            $difference /= $lengths[$j];
        }
        $difference = round($difference);
        if($difference != 1) $periods[$j].= "s";
        $text = "$difference $periods[$j-1] ago";
        return $text;
    }
}

If you look, I am leaving the arrays alone so you can still have seconds be put into your return value but it seems this should fix the logic error.

How to remove division by zero from this function?

3 Answers3