Sometimes, you need to add pad a number with leading zeros like numbers displayed in electrical devices.
To add leading zeros to numbers in PHP, you need to format your number as a string using the sprintf() function.
Here’s an example of creating a 4 digit number with sprintf():
<?php
// 👇 4 digit pad numbers
print sprintf("%04d", 333); // 0333
print PHP_EOL;
print sprintf("%04d", 1234); // 1234
print PHP_EOL;
print sprintf("%04d", 12); // 0012
?>
In the sprintf() function above, the format of the string is defined as “format the integer with 4 digits (4d) and pad it with leading zeros (0)”.
To change the format, you only need to adjust the number before the d letter.
The example below shows how to create 6 and 8 digit numbers:
<?php
// 👇 6 digit pad numbers
print sprintf("%06d", 1234); // 001234
print PHP_EOL;
// 👇 8 digit pad numbers
print sprintf("%08d", 1234); // 00001234
?>
Because numbers in PHP can’t have leading zeros naturally, you need to format the numbers using the sprintf() function.
You can also format negative numbers with leading zeros:
<?php
// 👇 6 digit pad numbers
print sprintf("%06d", -123); // -00123
print PHP_EOL;
print sprintf("%06d", -654); // -00654
?>
Alternatively, you can also use the str_pad() function to pad numbers with leading zeros.
But this function can’t be used to pad negative numbers as shown below:
<?php
// 👇 6 digit pad numbers
print str_pad(1234, 6, 0, STR_PAD_LEFT); // 001234
print PHP_EOL;
// 👇 8 digit pad numbers
print str_pad(1234, 8, 0, STR_PAD_LEFT); // 00001234
print PHP_EOL;
// 👇 negative number has wrong format
print str_pad(-1234, 6, 0, STR_PAD_LEFT); // 0-1234
?>
Padding negative numbers with the str_pad() function will produce an invalid format.
But if you never need to format negative numbers with leading zeros, then it’s fine to use the str_pad() function.