Php For loop not working properly inside another for loop?

Question

Following is my code. The first part works perfectly, but the second loop is not producing any results. What this is doing is that it looks for the timetable, then takes out the classes in that, copies all the that and makes a new timtable with same data but a different name.

The other for loop is to add students into the classes of the time table. Ca some one be kind enough and help me out in this as I have been hitting my head on the wall for it now for 5 days.

Thank you in advance. The code:

    <?php
$Q = "INSERT INTO time_table(name, term, year) VALUES
               ('".$name."', '".$term."', '".$year."')";
$res = $db->query($Q);
//for generating the max table id
        $sql2 = "select MAX(table_id) as table_id 
        from time_table 
        ";
        $res2 = $db->query($sql2);
        $count2 = $res2->num_rows;
        $row2 = $res2->fetch_assoc();

      $table_id = $row2['table_id'];
$Q = "SELECT class_id as tcid, day as d, teacher_id as tei, location as l
 FROM class_time_table 
 WHERE term='".$copy."'";
$res = $db->query($Q);
$num_results = $res->num_rows;
      for ($i = 0; $i <$num_results; $i++) {
         $row = $res->fetch_assoc();
            $Q4 = "SELECT * FROM students_class WHERE class_id = '".$row['tcid']."' and term = '".$copy."'";
            $res4 = $db->query($Q4);
            $row2 = $res4->fetch_assoc();
            //for generating the max table id
            $class_sysq = "select MAX(class_sys_id) as class_sys_id 
            from students_class 
            ";
            $class_sysr = $db->query($class_sysq);
            $count_class_sys = $class_sysr->num_rows;
            $class_row = $class_sysr->fetch_assoc();

            $class_sys_idf = $class_row['class_sys_id']+1;
            $Q5 = "INSERT INTO students_class (class_sys_id, teachers_id, location, max_students, class_term_fee, class_name, class_sub_name, term, year) VALUES ('".$class_sys_idf."', '".$row2['teachers_id']."', '".$row2['location']."', '".$row2['max_students']."', '".$row2['class_term_fee']."', '".$row2['class_name']."', '".$row2['class_sub_name']."', '".$term."', '".$year."')";
            $res5 = $db->query($Q5);
            //for generating the max table id
            $max_c_id = "select MAX(class_id) as ci 
            from students_class 
            ";
            $r_mci = $db->query($max_c_id);
            $count_class_sys = $r_mci->num_rows;
            $mci_row = $r_mci->fetch_assoc();
            $max_c_idf = $mci_row['ci'];

            $query2 = "INSERT INTO class_time_table(class_id, teacher_id, table_id, location, day, term, year) VALUES
               ('".$max_c_idf."', '".$row['tei']."', '".$table_id."', '".$row['l']."', '".$row['d']."', '".$term."', '".$year."')";
            $result2 = $db->query($query2);

        $student_q = "SELECT students.first_name as fn, students.last_name as ln, students.email as e, students.mobile_phone as mp, students.home_phone as hp, students.gender as g, students.dob as dob, students.term_fee as tf, students.join_date as jd, students.date_added as da, student_attending_class.class_id as ci FROM students, student_attending_class, class_time_table where students.student_sys_id = student_attending_class.student_id and student_attending_class.class_id = class_time_table.class_id and class_time_table.class_id = '".$row['tcid']."'";
            $student_res = $db->query($student_q);
            $student_num_results = $student_res->num_rows;
            for ($i = 0; $i < $student_num_results; $i++) {
            $theRow = $student_res->fetch_assoc();

            //for generating the new system id
            $sql3 = "select MAX(student_sys_id) as ssi 
            from students";
            $res3 = $db->query($sql3);
            $count3 = $res3->num_rows;
            $row8 = $res3->fetch_assoc();
            $student_system_num = $row8['ssi']+1;

            $query10 = "INSERT INTO students(student_sys_id, first_name, last_name, email, mobile_phone, home_phone, gender, dob, fee_due, registration_fee, term_fee, fee_paid, join_date, date_added) VALUES
               ('".$student_system_num."', '".$theRow['fn']."', '".$theRow['ln']."', '".$theRow['e']."', '".$theRow['mp']."', '".$theRow['hp']."', '".$theRow['g']."', '".$theRow['dob']."', '".$theRow['tf']."', 0, '".$theRow['tf']."', 0, '".$theRow['jd']."', '".$theRow['da']."')";
            $result10 = $db->query($query10);
            $query11 = "INSERT INTO student_attending_class(class_id, student_id, waiting_list) VALUES ('".$max_c_idf."', '".$student_system_num."', '0')";
            $result11 = $db->query($query11);

            }

        }   


?>

What values does $student_res->num_rows/$student_num_results get during that loop? Is it even higher than 0? — Derk Arts, Feb 07 '13 at 07:44

score 1 · Accepted Answer · answered Feb 07 '13 at 07:44

1

Don't use $i in the second loop but $n for instance.

answered Feb 07 '13 at 07:44

Rembunator

1,305
7
13

that sounds like you almost said the words in diamond, i have not tried it yet but i think that will do the job...logically i mean. Thanks mate! – olbanana Feb 07 '13 at 11:07
though it still shows a timeout, doesnt completely reload the page but its working out the calculations....any thing on that bro? – olbanana Feb 07 '13 at 11:32
Maybe increase max_execution_time? – Derk Arts Feb 07 '13 at 17:07

score 0 · Answer 2 · answered Feb 07 '13 at 07:44

0

i m not sure but you used same variable $i in both loop so maybe because of that your second loop not working. try another variable $j in second loop.

answered Feb 07 '13 at 07:44

Devang Rathod

6,650
2
23
32

score 0 · Answer 3 · answered Feb 07 '13 at 07:46

0

The code is poorly formatted, so it's easy to miss that you're using the same variable for both loops, hence when the second loop begins, the first loses track of its progress. Use foreach(), or a different variable name for the second loop.

answered Feb 07 '13 at 07:46

deed02392

4,799
2
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48

score 0 · Answer 4 · answered Feb 07 '13 at 07:49

0

You are probably getting a timeout due to having nested loops which both use the same variable, $i and it just keeps incrementing.

Try changing the second loop like so:

for($j = 0; $j < $student_num_results; $j++){
   ...
}

answered Feb 07 '13 at 07:49

Alderis Shyti

278
1
8

i did that its still a timeout! – olbanana Feb 07 '13 at 11:11
though it still shows a timeout, doesnt completely reload the page but its working out the calculations....any thing on that bro? – olbanana Feb 07 '13 at 11:31
@KaziSaad Could be that PHP reaches its default 30 second timeout? Do your queries occupy the script for that long? – Alderis Shyti Feb 07 '13 at 11:55
@KaziSaad There is, though not advisable. Check [set_time_limit](http://php.net/manual/en/function.set-time-limit.php) if you want to change the limit value just for that script. Alternatively, if you have access to the php_ini file you can change `max_execution_time` and it will affect your application as a whole. My advice is optimizing your queries rather than altering execution times. – Alderis Shyti Feb 07 '13 at 13:34

Php For loop not working properly inside another for loop?

4 Answers4