What Does a Leading Zero Do for a PHP Int

Formatting a number with leading zeros in PHP

Use sprintf :

sprintf('%08d', 1234567);

Alternatively you can also use str_pad:

str_pad($value, 8, '0', STR_PAD_LEFT);

What does a leading zero do for a php int?

If you use a leading zero, the number is interpreted by PHP as an octal number. Thus, a 9 is not a valid part of the number and the parser stops there:

  0730320 (base 8)
=  7 * 8^5 + 3 * 8^4 + 3 * 8^2 + 2 * 8^1
=  7 * 32768 + 3 * 4096 + 3 * 64 + 2 * 8 (base 10)
=  241872 (base 10)

How is Leading Zero working in php?

When you preceed integers with zero in PHP, in that instance, 029.

It becomes octal.

So when you echo that, it will convert to its decimal form.

Which results to:

echo 016; //14 (decimal) valid octal

echo 029; // 2 (decimal) -  Invalid octal

Actually, its here stated in the manual

Valid octal:

octal       : 0[0-7]+

Note: Prior to PHP 7, if an invalid digit was given in an octal integer (i.e. 8 or 9), the rest of the number was ignored. Since PHP 7, a parse error is emitted.

How to keep leading zeros in PHP integer

You cannot keep leading zeros in integer. You can either keep them in a string or add at output time, using sprintf(), str_pad(), etc.

Adding numbers with leading zeros

With str_pad:

For($i=1; $i<=44; $i++){
    Echo str_pad($i,5,"0",STR_PAD_LEFT) ."\n";
}

https://3v4l.org/Pe3M2

Str_pad(start number, length of string you want, what type of padding, where to place the padding [left/right])

The leading zero is changing the result in php

Appending 0 to the front of a number in PHP is making it octal.

16 in octal is equivalent to 14 in decimal.

So , 14/2 = 7 is the answer.

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

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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