Leading zero to numbers in PHP

Here's a simple code snippet to add leading zero to a number. How to add leading zero to date

#1

<?php 

function leadingzero ($num,$fill) { 

 while (strlen($num)<$fill) { 

         $num = "0".$num;
    }
    return $num; 

}

echo leadingzero(100, 3);

?>

Output: 000100

#2

<?php

$x = 1;
$y = sprintf("%03d",$x);
echo $y;

?>

Output: 001

#3

Print a day in double digit; Leading zero for first 9 days.

<?php

for ($num = 1; $num <= 31; $num++) {
if($num<10)
$day = "0$num"; // add the zero
else
$day = "$num"; // don't add the zero
echo "<p>$day</p>";

}

?>

Output:

01

02

03

04

05

06

07

08

09

10

.

.

.

31