How to prefix a positive number with plus sign in PHP

Question

I need to design a function to return negative numbers unchanged but should add a + sign at the start of the number if its already no present.

Example:

Input     Output
----------------
+1         +1
1          +1
-1         -1

It will get only numeric input.

function formatNum($num)
{
# something here..perhaps a regex?
}

This function is going to be called several times in echo/print so the quicker the better.

Update:

Thank you all for the answers. I must tell the sprintf based solution is really fast.

Answer 1

You can use regex as:

function formatNum($num){
    return preg_replace('/^(\d+)$/',"+$1",$num);
}

But I would suggest not using regex for such a trivial thing. Its better to make use of sprintf here as:

function formatNum($num){
    return sprintf("%+d",$num);
}

From PHP Manual for sprintf:

An optional sign specifier that forces a sign (- or +) to be used on a number. By default, only the - sign is used on a number if it's negative. This specifier forces positive numbers to have the + sign attached as well, and was added in PHP 4.3.0.

Answer 2

function formatNum($num) {
   return ($num>0)?'+'.$num:$num;
}

Answer 3

function formatNum($num) {
  $num = (int) $num; // or (float) if you'd rather
  return (($num >= 0) ? '+' : '') . $num; // implicit cast back to string
}

Answer 4

The sprintf solution provided by @unicornaddict is very nice and probably the most elegant way to go. Just thought I'd provide an alternative anyway. Not sure how they measure up in speed.

// Non float safe version
function formatNum($num) {
    return (abs($num) == $num ? '+' : '') . intval($num);
}

// Float safe version
function formatNum($num) {
    return 
        (abs($num) == $num ? '+' : '') 
        . (intval($num) == $num ? intval($num) : floatval($num));
}

// Float safe version, alternative
function formatNum($num) {
    return 
        (abs($num) == $num ? '+' : '') 
        // Add '1' to $num to implicitly cast it to a number
        . (is_float($num + 1) ? floatval($num) : intval($num));
}