[moodle.git] / mod / quiz / lib.php

<?PHP  // $Id$

/// Library of function for module quiz

/// CONSTANTS ///////////////////////////////////////////////////////////////////

define("GRADEHIGHEST", "1");
define("GRADEAVERAGE", "2");
define("ATTEMPTFIRST", "3");
define("ATTEMPTLAST",  "4");
$QUIZ_GRADE_METHOD = array ( GRADEHIGHEST => get_string("gradehighest", "quiz"),
                             GRADEAVERAGE => get_string("gradeaverage", "quiz"),
                             ATTEMPTFIRST => get_string("attemptfirst", "quiz"),
                             ATTEMPTLAST  => get_string("attemptlast", "quiz"));

define("SHORTANSWER", "1");
define("TRUEFALSE",   "2");
define("MULTICHOICE", "3");
$QUIZ_QUESTION_TYPE = array ( SHORTANSWER => get_string("shortanswer", "quiz"),
                              TRUEFALSE   => get_string("truefalse", "quiz"),
                              MULTICHOICE => get_string("multichoice", "quiz"));


/// FUNCTIONS ///////////////////////////////////////////////////////////////////

function quiz_add_instance($quiz) {
/// Given an object containing all the necessary data, 
/// (defined by the form in mod.html) this function 
/// will create a new instance and return the id number 
/// of the new instance.

    $quiz->timemodified = time();

    if (!$quiz->id = insert_record("quiz", $quiz)) {
        return false;  // some error occurred
    }

    // The grades for every question in this quiz are stored in an array
    if ($quiz->grades) {
        foreach ($quiz->grades as $question => $grade) {
            $questiongrade->quiz = $quiz->id;
            $questiongrade->question = $question;
            $questiongrade->grade = $grade;
            if (!insert_record("quiz_question_grades", $questiongrade)) {
                return false;
            }
        }
    }
    
    return $quiz->id;
}


function quiz_update_instance($quiz) {
/// Given an object containing all the necessary data, 
/// (defined by the form in mod.html) this function 
/// will update an existing instance with new data.

    $quiz->timemodified = time();
    $quiz->id = $quiz->instance;

    if (!update_record("quiz", $quiz)) {
        return false;  // some error occurred
    }


    // The grades for every question in this quiz are stored in an array
    // Insert or update records as appropriate

    $existing = get_records("quiz_question_grades", "quiz", $quiz->id, "", "question,grade,id");

    if ($quiz->grades) {
        foreach ($quiz->grades as $question => $grade) {
            $questiongrade->quiz = $quiz->id;
            $questiongrade->question = $question;
            $questiongrade->grade = $grade;
            if (isset($existing[$question])) {
                if ($existing[$question]->grade != $grade) {
                    $questiongrade->id = $existing[$question]->id;
                    if (!update_record("quiz_question_grades", $questiongrade)) {
                        return false;
                    }
                }
            } else {
                if (!insert_record("quiz_question_grades", $questiongrade)) {
                    return false;
                }
            }
        }
    }
    
    return true;
}


function quiz_delete_instance($id) {
/// Given an ID of an instance of this module, 
/// this function will permanently delete the instance 
/// and any data that depends on it.  

    if (! $quiz = get_record("quiz", "id", "$id")) {
        return false;
    }

    $result = true;

    if ($attempts = get_record("quiz_attempts", "quiz", "$quiz->id")) {
        foreach ($attempts as $attempt) {
            if (! delete_records("quiz_responses", "attempt", "$attempt->id")) {
                $result = false;
            }
        }
    }

    if (! delete_records("quiz_attempts", "quiz", "$quiz->id")) {
        $result = false;
    }

    if (! delete_records("quiz_grades", "quiz", "$quiz->id")) {
        $result = false;
    }

    if (! delete_records("quiz_question_grades", "quiz", "$quiz->id")) {
        $result = false;
    }

    if (! delete_records("quiz", "id", "$quiz->id")) {
        $result = false;
    }

    return $result;
}

function quiz_user_outline($course, $user, $mod, $quiz) {
/// Return a small object with summary information about what a 
/// user has done with a given particular instance of this module
/// Used for user activity reports.
/// $return->time = the time they did it
/// $return->info = a short text description

    return $return;
}

function quiz_user_complete($course, $user, $mod, $quiz) {
/// Print a detailed representation of what a  user has done with 
/// a given particular instance of this module, for user activity reports.

    return true;
}

function quiz_print_recent_activity(&$logs, $isteacher=false) {
/// Given a list of logs, assumed to be those since the last login 
/// this function prints a short list of changes related to this module
/// If isteacher is true then perhaps additional information is printed.
/// This function is called from course/lib.php: print_recent_activity()

    global $CFG, $COURSE_TEACHER_COLOR;

    return $content;  // True if anything was printed, otherwise false
}

function quiz_cron () {
/// Function to be run periodically according to the moodle cron
/// This function searches for things that need to be done, such 
/// as sending out mail, toggling flags etc ... 

    global $CFG;

    return true;
}


//////////////////////////////////////////////////////////////////////////////////////
/// Any other quiz functions go here.  Each of them must have a name that 
/// starts with quiz_

function  quiz_print_question($number, $questionid, $grade, $courseid) {
/// Prints a quiz question, any format
    
    if (!$question = get_record("quiz_questions", "id", $questionid)) {
        notify("Error: Question not found!");
    }

    $stranswer = get_string("answer", "quiz");
    $strmarks  = get_string("marks", "quiz");

    echo "<TABLE WIDTH=100% CELLSPACING=10><TR><TD NOWRAP WIDTH=100 VALIGN=top>";
    echo "<P ALIGN=CENTER><B>$number</B><BR><FONT SIZE=1>$grade $strmarks</FONT></P>";
    print_spacer(1,100);
    echo "</TD><TD VALIGN=TOP>";

    switch ($question->type) {
       case SHORTANSWER: 
           if (!$options = get_record("quiz_shortanswer", "question", $question->id)) {
               notify("Error: Missing question options!");
           }
           echo text_to_html($question->questiontext);
           if ($question->image) {
               print_file_picture($question->image, $courseid, 200);
           }
           echo "<P ALIGN=RIGHT>$stranswer: <INPUT TYPE=TEXT NAME=q$question->id SIZE=20></P>";
           break;

       case TRUEFALSE:
           if (!$options = get_record("quiz_truefalse", "question", $question->id)) {
               notify("Error: Missing question options!");
           }
           if (!$true = get_record("quiz_answers", "id", $options->true)) {
               notify("Error: Missing question answers!");
           }
           if (!$false = get_record("quiz_answers", "id", $options->false)) {
               notify("Error: Missing question answers!");
           }
           if (!$true->answer) {
               $true->answer = get_string("true", "quiz");
           }
           if (!$false->answer) {
               $false->answer = get_string("false", "quiz");
           }
           echo text_to_html($question->questiontext);
           if ($question->image) {
               print_file_picture($question->image, $courseid, 200);
           }
           echo "<P ALIGN=RIGHT>$stranswer:&nbsp;&nbsp;";
           echo "<INPUT TYPE=RADIO NAME=\"q$question->id\" VALUE=\"$true->id\">$true->answer";
           echo "&nbsp;&nbsp;&nbsp;";
           echo "<INPUT TYPE=RADIO NAME=\"q$question->id\" VALUE=\"$false->id\">$false->answer</P>";
           break;

       case MULTICHOICE:
           if (!$options = get_record("quiz_multichoice", "question", $question->id)) {
               notify("Error: Missing question options!");
           }
           if (!$answers = get_records_list("quiz_answers", "id", $options->answers)) {
               notify("Error: Missing question answers!");
           }
           echo text_to_html($question->questiontext);
           if ($question->image) {
               print_file_picture($question->image, $courseid, 200);
           }
           echo "<TABLE ALIGN=right>";
           echo "<TR><TD valign=top>$stranswer:&nbsp;&nbsp;</TD><TD>";
           echo "<TABLE ALIGN=right>";
           $answerids = explode(",", $options->answers);
           foreach ($answerids as $key => $answerid) {
               $answer = $answers[$answerid];
               $qnum = $key + 1;
               echo "<TR><TD valign=top>";
               if ($options->single) {
                   echo "<INPUT TYPE=RADIO NAME=q$question->id VALUE=\"$answer->id\">";
               } else {
                   echo "<INPUT TYPE=CHECKBOX NAME=q$question->id"."a$answer->id VALUE=\"$answer->id\">";
               }
               echo "</TD>";
               echo "<TD valign=top>$qnum. $answer->answer</TD>";
               echo "</TR>";
           }
           echo "</TABLE>";
           echo "</TABLE>";
           break;

       default: 
           notify("Error: Unknown question type!");
    }

    echo "</TD></TR></TABLE>";
}

function quiz_print_quiz_questions($quiz, $results=NULL) {
// Prints a whole quiz on one page.

    if (!$quiz->questions) {
        notify("No questions have been defined!", "view.php?id=$cm->id");
        return false;
    }

    $questions = explode(",", $quiz->questions);

    if (!$grades = get_records_list("quiz_question_grades", "question", $quiz->questions, "", "question,grade")) {
        notify("No grades were found for these questions!");
        return false;
    }

    echo "<FORM METHOD=POST ACTION=attempt.php>";
    echo "<INPUT TYPE=hidden NAME=q VALUE=\"$quiz->id\">";
    foreach ($questions as $key => $questionid) {
        print_simple_box_start("CENTER", "90%");
        quiz_print_question($key+1, $questionid, $grades[$questionid]->grade, $quiz->course);
        print_simple_box_end();
        echo "<BR>";
    }
    echo "<CENTER><INPUT TYPE=submit VALUE=\"".get_string("savemyanswers", "quiz")."\"></CENTER>";
    echo "</FORM>";

    return true;
}
 
function quiz_get_default_category($courseid) {
    if ($categories = get_records("quiz_categories", "course", $courseid, "id")) {
        foreach ($categories as $category) {
            return $category;   // Return the first one (lowest id)
        }
    }

    // Otherwise, we need to make one
    $category->name = get_string("default", "quiz");
    $category->info = get_string("defaultinfo", "quiz");
    $category->course = $courseid;
    $category->publish = 0;

    if (!$category->id = insert_record("quiz_categories", $category)) {
        notify("Error creating a default category!");
        return false;
    }
    return $category;
}

function quiz_print_category_form($course, $current) {
// Prints a form to choose categories

    if (!$categories = get_records_sql_menu("SELECT id,name FROM quiz_categories 
                                             WHERE course='$course->id' OR publish = '1'
                                             ORDER by name ASC")) {
        if (!$category = quiz_get_default_category($course->id)) {
            notify("Error creating a default category!");
            return false;
        }
        $categories[$category->id] = $category->name;
    }
    $strcategory = get_string("category", "quiz");
    $strshow = get_string("show", "quiz");
    $stredit = get_string("edit");
    $strdelete = get_string("delete");
    $strnew = get_string("new");

    echo "<FORM METHOD=POST ACTION=edit.php>"; 
    echo "<B>$strcategory:</B>&nbsp;";
    choose_from_menu($categories, "cat", "$current");
    echo "<INPUT TYPE=submit NAME=catshow VALUE=\"$strshow\">";
    echo "<INPUT TYPE=submit NAME=catedit VALUE=\"$stredit\">";
    echo "<INPUT TYPE=submit NAME=catdelete VALUE=\"$strdelete\">&nbsp;";
    echo "<INPUT TYPE=submit NAME=catnew VALUE=\"$strnew\">";
    echo "</FORM>";
}


function quiz_get_all_question_grades($questionlist, $quizid) {
// Given a list of question IDs, finds grades or invents them to 
// create an array of matching grades

    $questions = get_records_sql("SELECT * FROM quiz_question_grades 
                                  WHERE quiz = '$quizid' 
                                    AND question IN ($questionlist)");

    $list = explode(",", $questionlist);
    $grades = array();

    foreach ($list as $qid) {
        if (isset($questions[$qid])) {
            $grades[$qid] = $questions[$qid]->grade;
        } else {
            $grades[$qid] = 1;
        }
    }
    return $grades;
}


function quiz_print_question_list($questionlist, $grades) {
// Prints a list of quiz questions in a small layout form with knobs
// $questionlist is comma-separated list
// $grades is an array of corresponding grades

    global $THEME;

    if (!$questionlist) {
        echo "<P align=center>";
        print_string("noquestions", "quiz");
        echo "</P>";
        return;
    }

    $order = explode(",", $questionlist);

    if (!$questions = get_records_list("quiz_questions", "id", $questionlist)) {
        error("No questions were found!");
    }

    $strorder = get_string("order");
    $strquestionname = get_string("questionname", "quiz");
    $strgrade = get_string("grade");
    $strdelete = get_string("delete");
    $stredit = get_string("edit");
    $strmoveup = get_string("moveup");
    $strmovedown = get_string("movedown");
    $strsavegrades = get_string("savegrades", "quiz");

    for ($i=10; $i>=0; $i--) {
        $gradesmenu[$i] = $i;
    }
    $count = 0;
    $sumgrade = 0;
    $total = count($order);
    echo "<FORM METHOD=post ACTION=edit.php>";
    echo "<TABLE BORDER=0 CELLPADDING=5 CELLSPACING=2 WIDTH=\"100%\">";
    echo "<TR><TH WIDTH=10 COLSPAN=3>$strorder</TH><TH align=left WIDTH=\"100%\">$strquestionname</TH><TH WIDTH=10>$strgrade</TH><TH WIDTH=10>$stredit</TH></TR>";
    foreach ($order as $qnum) {
        $count++;
        echo "<TR BGCOLOR=\"$THEME->cellcontent\">";
        echo "<TD>$count</TD>";
        echo "<TD>";
        if ($count != 1) {
            echo "<A TITLE=\"$strmoveup\" HREF=\"edit.php?up=$qnum\"><IMG 
                 SRC=\"../../pix/t/up.gif\" BORDER=0></A>";
        }
        echo "</TD>";
        echo "<TD>";
        if ($count != $total) {
            echo "<A TITLE=\"$strmovedown\" HREF=\"edit.php?down=$qnum\"><IMG 
                 SRC=\"../../pix/t/down.gif\" BORDER=0></A>";
        }
        echo "</TD>";
        echo "<TD>".$questions[$qnum]->name."</TD>";
        echo "<TD>";
        choose_from_menu($gradesmenu, "q$qnum", $grades[$qnum], "");
        echo "<TD>";
            echo "<A TITLE=\"$strdelete\" HREF=\"edit.php?delete=$qnum\"><IMG 
                 SRC=\"../../pix/t/delete.gif\" BORDER=0></A>&nbsp;";
            echo "<A TITLE=\"$stredit\" HREF=\"question.php?id=$qnum\"><IMG 
                 SRC=\"../../pix/t/edit.gif\" BORDER=0></A>";
        echo "</TD>";

        $sumgrade += $grades[$qnum];
    }
    echo "<TR><TD COLSPAN=3><TD ALIGN=right>";
    echo "<INPUT TYPE=submit VALUE=\"$strsavegrades:\">";
    echo "<INPUT TYPE=hidden NAME=grade VALUE=\"save\">";
    echo "<TD ALIGN=LEFT BGCOLOR=\"$THEME->cellcontent\">";
    echo "<B>$sumgrade</B>";
    echo "</TD><TD></TD></TR>";
    echo "</TABLE>";
    echo "</FORM>";

    return $sumgrade;
}


function quiz_print_cat_question_list($categoryid) {
// Prints a form to choose categories

    global $THEME, $QUIZ_QUESTION_TYPE;

    $strcategory = get_string("category", "quiz");
    $strquestion = get_string("question", "quiz");
    $strnoquestions = get_string("noquestions", "quiz");
    $strselect = get_string("select", "quiz");
    $strcreatenewquestion = get_string("createnewquestion", "quiz");
    $strquestionname = get_string("questionname", "quiz");
    $strdelete = get_string("delete");
    $stredit = get_string("edit");
    $straddselectedtoquiz = get_string("addselectedtoquiz", "quiz");

    if (!$categoryid) {
        echo "<P align=center>";
        print_string("selectcategoryabove", "quiz");
        echo "</P>";
        return;
    }

    if (!$category = get_record("quiz_categories", "id", "$categoryid")) {
        notify("Category not found!");
        return;
    }
    echo "<P><B>$strcategory:</B> $category->name</P>\n";
    echo text_to_html($category->info);

    echo "<FORM METHOD=GET ACTION=question.php>"; 
    echo "<B>$strquestion:</B>&nbsp;";
    choose_from_menu($QUIZ_QUESTION_TYPE, "type", "", "");
    echo "<INPUT TYPE=hidden NAME=category VALUE=\"$category->id\">";
    echo "<INPUT TYPE=submit NAME=new VALUE=\"$strcreatenewquestion\">";
    echo "</FORM>";

    if (!$questions = get_records("quiz_questions", "category", $category->id)) {
        echo "<P align=center>";
        print_string("noquestions", "quiz");
        echo "</P>";
        return;
    }

    $canedit = isteacher($category->course);

    echo "<FORM METHOD=post ACTION=edit.php>";
    echo "<TABLE BORDER=0 CELLPADDING=5 CELLSPACING=2 WIDTH=\"100%\">";
    echo "<TR><TH width=10>$strselect</TH><TH width=* align=left>$strquestionname</TH>";
    if ($canedit) {
        echo "<TH width=10>$stredit</TH>";
    }
    echo "</TR>";
    foreach ($questions as $question) {
        echo "<TR BGCOLOR=\"$THEME->cellcontent\">";
        echo "<TD ALIGN=CENTER>";
        echo "<INPUT TYPE=CHECKBOX NAME=q$question->id VALUE=\"1\">";
        echo "</TD>";
        echo "<TD>".$question->name."</TD>";
        if ($canedit) {
            echo "<TD>";
                echo "<A TITLE=\"$strdelete\" HREF=\"question.php?delete=$question->id\"><IMG 
                     SRC=\"../../pix/t/delete.gif\" BORDER=0></A>&nbsp;";
                echo "<A TITLE=\"$stredit\" HREF=\"question.php?id=$question->id\"><IMG 
                     SRC=\"../../pix/t/edit.gif\" BORDER=0></A>";
            echo "</TD></TR>";
        }
        echo "</TR>";
    }
    echo "<TR><TD COLSPAN=3>";
    echo "<INPUT TYPE=hidden NAME=add VALUE=\"1\">";
    echo "<INPUT TYPE=submit VALUE=\"<< $straddselectedtoquiz\">";
    echo "</TD></TR>";
    echo "</TABLE>";
    echo "</FORM>";
}


function quiz_get_user_attempts($quizid, $userid) {
// Returns a list of all attempts by a user
    return get_records_sql("SELECT * FROM quiz_attempts WHERE quiz = '$quizid' and user = '$userid' ORDER by attempt ASC");
}

function quiz_get_best_grade($quizid, $userid) {
/// Get the best current grade for a particular user in a quiz
    if (!$grade = get_record_sql("SELECT * FROM quiz_grades WHERE quiz = '$quizid' and user = '$userid'")) {
        return 0;
    }

    return $grade->grade;
}

function quiz_get_grade_records($quiz) {
/// Gets all info required to display the table of quiz results
/// for report.php

    return get_records_sql("SELECT qg.*, u.firstname, u.lastname, u.picture 
                            FROM quiz_grades qg, user u
                            WHERE qg.quiz = '$quiz->id'
                              AND qg.user = u.id");
}

function quiz_save_best_grade($quiz, $user) {
/// Calculates the best grade out of all attempts at a quiz for a user,
/// and then saves that grade in the quiz_grades table.

    if (!$attempts = quiz_get_user_attempts($quiz->id, $user->id)) {
        return false;
    }

    $bestgrade = quiz_calculate_best_grade($quiz, $attempts);
    $bestgrade = (($bestgrade / $quiz->sumgrades) * $quiz->grade);

    if ($grade = get_record_sql("SELECT * FROM quiz_grades WHERE quiz='$quiz->id' AND user='$user->id'")) {
        $grade->grade = $bestgrade;
        $grade->timemodified = time();
        if (!update_record("quiz_grades", $grade)) {
            return false;
        }
    } else {
        $grade->quiz = $quiz->id;
        $grade->user = $user->id;
        $grade->grade = $bestgrade;
        $grade->timemodified = time();
        if (!insert_record("quiz_grades", $grade)) {
            return false;
        }
    }
    return true;
}


function quiz_get_answers($question) {
// Given a question, returns the correct answers and grades
    switch ($question->type) {
        case SHORTANSWER;       // Could be multiple answers
            return get_records_sql("SELECT a.*, sa.usecase, g.grade
                                      FROM quiz_shortanswer sa, quiz_answers a, quiz_question_grades g
                                     WHERE sa.question = '$question->id' 
                                       AND sa.question = a.question
                                       AND sa.question = g.question");
            break;

        case TRUEFALSE;         // Should be always two answers
            return get_records_sql("SELECT a.*, g.grade
                                      FROM quiz_answers a, quiz_question_grades g
                                     WHERE a.question = '$question->id' 
                                       AND a.question = g.question");
            break;

        case MULTICHOICE;       // Should be multiple answers
            return get_records_sql("SELECT a.*, mc.single, g.grade
                                      FROM quiz_multichoice mc, quiz_answers a, quiz_question_grades g
                                     WHERE mc.question = '$question->id' 
                                       AND mc.question = a.question 
                                       AND mc.question = g.question");
            break;

        default:
            return false;
    }
}

function quiz_calculate_best_grade($quiz, $attempts) {
/// Calculate the best grade for a quiz given a number of attempts by a particular user.

    switch ($quiz->grademethod) {

        case ATTEMPTFIRST:
            foreach ($attempts as $attempt) {
                return $attempt->sumgrades;
            }
            break;

        case ATTEMPTLAST:
            foreach ($attempts as $attempt) {
                $final = $attempt->sumgrades;
            }
            return $final;

        case GRADEAVERAGE:
            $sum = 0;
            $count = 0;
            foreach ($attempts as $attempt) {
                $sum += $attempt->sumgrades;
                $count++;
            }
            return (float)$sum/$count;

        default:
        case GRADEHIGHEST:
            $max = 0;
            foreach ($attempts as $attempt) {
                if ($attempt->sumgrades > $max) {
                    $max = $attempt->sumgrades;
                }
            }
            return $max;
    }
}

function quiz_save_attempt($quiz, $questions, $result, $attemptnum) {
/// Given a quiz, a list of attempted questions and a total grade 
/// this function saves EVERYTHING so it can be reconstructed later
/// if necessary.

    global $USER;

    // First let's save the attempt record itself

    $attempt->quiz = $quiz->id;
    $attempt->user = $USER->id;
    $attempt->attempt = $attemptnum;
    $attempt->sumgrades = $result->sumgrades;
    $attempt->timemodified = time();

    if (!$attempt->id = insert_record("quiz_attempts", $attempt)) {
        return false;
    }

    // Now let's save all the questions for this attempt

    foreach ($questions as $question) {
        $response->attempt = $attempt->id;
        $response->question = $question->id;
        $response->grade = $result->grades[$question->id];
        if ($question->answer) {
            $response->answer = implode(",",$question->answer);
        } else {
            $response->answer = "";
        }
        if (!insert_record("quiz_responses", $response)) {
            return false;
        }
    }
    return true;
}


function quiz_grade_attempt_results($quiz, $questions) {
/// Given a list of questions (including answers for each one)
/// this function does all the hard work of calculating the 
/// grades for each question, as well as a total grade for 
/// for the whole quiz.  It returns everything in a structure 
/// that looks like:
/// $result->sumgrades    (sum of all grades for all questions)
/// $result->percentage   (Percentage of grades that were correct)
/// $result->grade        (final grade result for the whole quiz)
/// $result->grades[]     (array of grades, indexed by question id)
/// $result->feedback[]   (array of feedback arrays, indexed by question id)

    if (!$questions) {
        error("No questions!");
    }
    
    $result->sumgrades = 0;

    global $db;
    $db->debug=true;

    foreach ($questions as $question) {
        if (!$answers = quiz_get_answers($question)) {
            error("No answers defined for question id $question->id!");
        }

        $grade    = 0;   // default
        $feedback = array ();

        switch ($question->type) {
            case SHORTANSWER:
                if ($question->answer) {
                    $question->answer = $question->answer[0];
                } else {
                    $question->answer = NULL;
                }
                foreach($answers as $answer) {  // There might be multiple right answers
                    $feedback[$answer->id] = $answer->feedback;
                    if (!$answer->usecase) {       // Don't compare case
                        $answer->answer = strtolower($answer->answer);
                        $question->answer = strtolower($question->answer);
                    }
                    if ($question->answer == $answer->answer) {
                        $grade = (float)$answer->fraction * $answer->grade;
                    }
                }
                break;


            case TRUEFALSE:
                if ($question->answer) {
                    $question->answer = $question->answer[0];
                } else {
                    $question->answer = NULL;
                }
                foreach($answers as $answer) {  // There should be two answers (true and false)
                    $feedback[$answer->id] = $answer->feedback;
                    if ($question->answer == $answer->id) {
                        $grade = (float)$answer->fraction * $answer->grade;
                    }
                }
                break;


            case MULTICHOICE:
                foreach($answers as $answer) {  // There will be multiple answers, perhaps more than one is right
                    $feedback[$answer->id] = $answer->feedback;
                    if ($question->answer) {
                        foreach ($question->answer as $questionanswer) {
                            if ($questionanswer == $answer->id) {
                                if ($answer->single) {
                                    $grade = (float)$answer->fraction * $answer->grade;
                                    continue;
                                } else {
                                    $grade += (float)$answer->fraction * $answer->grade;
                                }
                            }
                        }
                    }
                }
                break;

            
        }
        if ($grade < 0.0) {   // No negative grades
            $grade = 0.0;
        }

        $result->grades[$question->id] = $grade;
        $result->sumgrades += $grade;
        $result->feedback[$question->id] = $feedback;
    }

    $result->percentage = ($result->sumgrades / $quiz->sumgrades);
    $result->grade      = $result->percentage * $quiz->grade;

    return $result;
}
    
?>