<?php
    $name = trim(strip_tags(stripslashes($_POST['yname'])));
    $q1 = trim(strip_tags(stripslashes($_POST['q1'])));
    $q2 = trim(strip_tags(stripslashes($_POST['q2'])));
    $q3 = trim(strip_tags(stripslashes($_POST['q3'])));
    $q4 = trim(strip_tags(stripslashes($_POST['q4'])));

    $path_to_names_file = $_SERVER['DOCUMENT_ROOT'] . '/../names.txt';

    if ($name <> "" && $q1 <> "" && $q2 <> "" && $q3 <> "" && $q4 <> "") {
        if ($passing > 85) { //value checked in the more comprehensive script
            if(file_exists($path_to_names_file) && $names = file($path_to_names_file) && in_array($name, $names){
                echo "Sorry, but you took the exam already"; //$name has already taken exam
            }
            else { //if name doesn't match, the user is taking it first time. write the name to file for future check
                file_put_contents($path_to_names_file, "$name\n", FILE_APPEND); //append the file
                //....
            }
        }
        else {
            //...
        }
    }
    ?>