<?php
include ("mysql_connect.php");

if(isset($_POST["submit"])){

$correct_answers = 0;
$wrong_answers = 0;
$total = $_POST['total'] ;

$questions = $_POST['question_id']; //---an array with all question id's---

foreach($questions as $question_id){

$sql = mysqli_query($connection, "SELECT * FROM `answers` WHERE answers.question_id = '".$question_id ."' AND answers.correct = 1 ")or die(mysqli_error($connection));
$result = mysqli_fetch_assoc($sql);

//------check only those option values which are exist---------
if(isset($_POST['answers'.$question_id])){
$selected_choice = $_POST['answers'.$question_id];

   //----------checking answer choices----------
   if($selected_choice == $result['answer_id']){
        $correct_answers ++ ;
    }else{
        $wrong_answers ++;
    }
}
}

//------calculation for score percentage-----
$score = $correct_answers / $total;
$score = number_format($score * 100);

echo "your score is $score<br />";

//------count correct answers------------
if ($correct_answers > 0){
echo "<h2><span>You have $correct_answers correct answers</span></h2>";
}

//----------count wrong answers---------
if ($wrong_answers > 0) {
echo "<h2><span>You have $wrong_answers wrong answers</span></h2>" ;
}

}
?>

