errors messages with html and php

i have this code bellow:

if($name !=null && $email !=null && $password !=null && $gender !=null) {
   if(!filter_var($email, FILTER_VALIDATE_EMAIL)) {
    $emailError = "you should write a correct email";
   }
   if(strlen($password) < 6) {
    $passwordError = "password should consist from 6 charachters or more";
   }
   $result = mysqli_query($conn, $sql);
   if($result) {
    header("location:index.php");
   }else {
    echo "Error";
   }
} else {
    $msg = "you should fill all the form";
}
}

it doesn’t show any error when the email is not correct or the password is less than 6, and inserts data normally, I need to show for example two error messages if both password and email are not correct, how can I do it?

Answer

Amend your code so that

1. it will NOT execute the db query if there is/are error(s)
2. Display the errors if they exist.

<?php

//initialize the error messages to be blank

$emailError ="";
$passwordError="";

if($name !=null && $email !=null && $password !=null && $gender !=null) {
     if(!filter_var($email, FILTER_VALIDATE_EMAIL)) {
         $emailError = " you should enter a correct email ;";
      }
      if(strlen($password) < 6) {
          $passwordError = " password should consist of 6 characters or more ;";
      }

if ($emailError =="" && $passwordError=="") {

   $result = mysqli_query($conn, $sql);
     if($result) {
       header("location:index.php");
      } else {
       echo "Error";
      }

} else {

echo "You have the following error(s) :";  

  if ($emailError !=""){
    echo $emailError;
  }

  if ($passwordError !=""){
    echo $passwordError;
  }
}


} else {
//    $msg = "you should fill all the form";
    echo "you should enter all the required data in the form";
}


?>