PHP Form Validation with isset($_POST['name'])

Question

Code from Robin Nixon book:

if (isset($_POST['user'])) {
  $user = sanitizeString($_POST['user']);
  $pass = sanitizeString($_POST['pass']);
  if ($user == "" || $pass == "")
    $error = "Not all fields were entered<br><br>";
  else {
    $result = queryMysql("SELECT * FROM members WHERE user='$user'");
    if ($result - > num_rows)
      $error = "That username already exists<br><br>";
    else {
      queryMysql("INSERT INTO members VALUES('$user', '$pass')");
      die("<h4>Account created</h4>Please Log in.<br><br>");
    }
  }
}

why He use isset($_POST['user']) here ? Why he don't use isset($_POST['submit'] instead ?

Answer 1

The Code already missing a Closing bracket.

<?php
if (isset($_POST['user']))
{
$user = sanitizeString($_POST['user']);
$pass = sanitizeString($_POST['pass']);
if ($user == "" || $pass == "")
$error = "Not all fields were entered<br><br>";
else
{
$result = queryMysql("SELECT * FROM members WHERE user='$user'");
if ($result->num_rows)
$error = "That username already exists<br><br>";
else
{
queryMysql("INSERT INTO members VALUES('$user', '$pass')");
die("<h4>Account created</h4>Please Log in.<br><br>");
 } 
}
}
?>

The code now accepts if POST user is set. or if implement the code over your html form field submit! if you need to if POST submit check.. So what i wanna do? Please inform i can modify as you need.