PHP CPF validator

Question

Good afternoon, everyone,

I’d like to know what’s wrong with my Cpf validator, made in PHP. What happens, it validates my number, my mother’s, brother’s, girlfriend’s and grandma’s. But, when I test some CPF I took from a Cpf generator online, it valid some and others not.

Consider receiving the form CPF value via POST from a number field (No scores)

<?php 
require_once ("cabecalho.php");
$cpf = $_POST['cpf'];

if (strlen($cpf) != 11) {
    $_SESSION["danger"] = "O CPF deve conter 11 digítos. Preencha novamente.";
    header("Location: cpf.php");
    die();
}

$verificaJ = $cpf[9];
$verificaK = $cpf[10];

$J_letra = 10;
$J_array = array();
for ($i < 0; $i <= 8; $i++){
    $J_array[] = $cpf[$i] * $J_letra;
    $J_letra--;
    $J_soma = $J_soma + $J_array[$i];
}

$J_resto = $J_soma % 11;
$J_subtracao = 11 - $J_resto;

if ($J_subtracao > 9) {
    $J = 0;
    echo "J:" . $J . "<br> ";
} else {
    $J = $J_subtracao;
    echo "J else:" . $J . "<br>";
}

//Conseguindo K
$K_letra = 11;
$K_array = array();
for ($ii < 0; $ii <= 9; $ii++){
    $K_array[] = $cpf[$ii] * $K_letra;
    $K_letra--;
    $K_soma = $K_soma + $K_array[$ii];
}

$K_resto = $K_soma % 11;
$K_subtracao = 11 - $K_resto;
if ($K_subtracao > 9) {
    $K = 0;
    echo "K:" . $K . "<br> ";

} else {
    $K = $K_subtracao;
    echo "K:" . $K . "<br> ";

}

if ($verificaJ == $J && $verificaK == $K){
   echo "CPF VÁLIDO";
} else {
  echo "CPF INVÁLIDO";
}

Ps: I know the code is not very stylish. But please I want to know the error of this code, and don’t get one of the internet ready.

Answer 1

The error is in the value of $i in the loop for. The assigned value should be $i = 0 and not $i < 0. With that the $i only becomes valuable, and 1, after the first loop of the loop, ignoring the content 0 array, resulting in the wrong sum of calculations.

Just correct the value of $i in both ties for of the code, changing $i < 0 and $ii < 0 for $i = 0 and $ii = 0 respectively.

See the same code running in Javascript (valid Cpfs were generated on a CPF generator site):

function validaCPF($cpf){

   $verificaJ = $cpf[9];
   $verificaK = $cpf[10];
   
   $J_letra = 10;
   $J_array = [];
   $J_soma = 0;
   for ($i = 0; $i <= 8; $i++){
       $J_array.push($cpf[$i] * $J_letra);
       $J_letra--;
       $J_soma = $J_soma + $J_array[$i];
   }
   
   $J_resto = $J_soma % 11;
   $J_subtracao = 11 - $J_resto;
   
   if ($J_subtracao > 9) {
       $J = 0;
   } else {
       $J = $J_subtracao;
   }
   
   //Conseguindo K
   $K_letra = 11;
   $K_array = [];
   $K_soma = 0;
   for ($ii = 0; $ii <= 9; $ii++){
       $K_array.push($cpf[$ii] * $K_letra);
       $K_letra--;
       $K_soma = $K_soma + $K_array[$ii];
   }
   
   $K_resto = $K_soma % 11;
   $K_subtracao = 11 - $K_resto;
   if ($K_subtracao > 9) {
       $K = 0;
   
   } else {
       $K = $K_subtracao;
   
   }
   
   if ($verificaJ == $J && $verificaK == $K){
      return $cpf+": CPF VÁLIDO";
   } else {
     return $cpf+": CPF INVÁLIDO";
   }
}

console.log(validaCPF('59848265007')); // válido
console.log(validaCPF('59848265008')); // inválido
console.log(validaCPF('55688772034')); // válido
console.log(validaCPF('55688772033')); // inválido

<p>Digite um CPF</p>
<input type="text" id="cpf" style="width: 200px; font-size: 30px;">
<button onclick="console.clear(); console.log(validaCPF(document.getElementById('cpf').value))">OK</button>