Can you help me understand this simple PHP function, please? - php

Question

I would like to know how this function works so I can re-write it in ColdFusion. I've never programmed in PHP. I think, the function checks if $string is 11 numbers in length.
But how is it doing it?
Why is it using a loop instead of a simple len() function?
I read about str_pad(), and understand it. But what is the function of the loop iteration $i as a third argument? What's it doing?
if($this->check_fake($cpf, 11)) return FALSE;
function check_fake($string, $length)
{
for($i = 0; $i <= 9; $i++) {
$fake = str_pad("", $length, $i);
if($string === $fake) return(1);
}
}
The function is meant to validate a CPF, the Brazilian equivalent of a US SSN #. The CPF is 11 characters in length. Basically, I need to know what it's doing so I can write the function in Coldfusion.
If it's just a length, can't it be if (len(cpf) != 11) return false; ?
Here is the entire code snippet if it interests you:
<?
/*
*# Class VALIDATE - It validates Brazilian CPF/CNPJ numbers
*# Developer: André Luis Cupini - andre#neobiz.com.br
************************************************************/
class VALIDATE
{
/*
*# Remove ".", "-", "/" of the string
*****************************************************/
function cleaner($string)
{
return $string = str_replace("/", "", str_replace("-", "", str_replace(".", "", $string)));
}
/*
*# Check if the number is fake
*****************************************************/
function check_fake($string, $length)
{
for($i = 0; $i <= 9; $i++) {
$fake = str_pad("", $length, $i);
if($string === $fake) return(1);
}
}
/*
*# Validates CPF
*****************************************************/
function cpf($cpf)
{
$cpf = $this->cleaner($cpf);
$cpf = trim($cpf);
if(empty($cpf) || strlen($cpf) != 11) return FALSE;
else {
if($this->check_fake($cpf, 11)) return FALSE;
else {
$sub_cpf = substr($cpf, 0, 9);
for($i =0; $i <=9; $i++) {
$dv += ($sub_cpf[$i] * (10-$i));
}
if ($dv == 0) return FALSE;
$dv = 11 - ($dv % 11);
if($dv > 9) $dv = 0;
if($cpf[9] != $dv) return FALSE;
$dv *= 2;
for($i = 0; $i <=9; $i++) {
$dv += ($sub_cpf[$i] * (11-$i));
}
$dv = 11 - ($dv % 11);
if($dv > 9) $dv = 0;
if($cpf[10] != $dv) return FALSE;
return TRUE;
}
}
}
}
?>

Answer 1

it basically makes sure the number isn't:
11111111111
22222222222
33333333333
44444444444
55555555555
etc...

Answer 2

With comments:
function check_fake($string, $length)
{
// for all digits
for($i = 0; $i <= 9; $i++)
{
// create a $length characters long string, consisting of
// $length number of the number $i
// e.g. 00000000000
$fake = str_pad("", $length, $i);
// return true if the provided CPN is equal
if($string === $fake) return(1);
}
}
In short, it tests to see if the provided string is just the same digit repeated $length times.