PHP prepend leading zero before single digit number, on-the-fly

php string numbers zero
Ben picture Ben · Apr 14, 2011 · Viewed 294.3k times · Source

PHP - Is there a quick, on-the-fly method to test for a single character string, then prepend a leading zero?

Example:

$year = 11;
$month = 4;

$stamp = $year.add_single_zero_if_needed($month);  // Imaginary function

echo $stamp; // 1104

Answer

Kirk Beard picture Kirk Beard · Apr 14, 2011

You can use sprintf: http://php.net/manual/en/function.sprintf.php

<?php
$num = 4;
$num_padded = sprintf("%02d", $num);
echo $num_padded; // returns 04
?>

It will only add the zero if it's less than the required number of characters.

Edit: As pointed out by @FelipeAls:

When working with numbers, you should use %d (rather than %s), especially when there is the potential for negative numbers. If you're only using positive numbers, either option works fine.

For example:

sprintf("%04s", 10); returns 0010
sprintf("%04s", -10); returns 0-10

Where as:

sprintf("%04d", 10); returns 0010
sprintf("%04d", -10); returns -010

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