Loop and Undefined index php - 【StackMirror】|php|loops|checkbox

This is my first time using PHP and im learning everything from w3school. My question :

1 Loop

I have a database for seat booking which is ex : A1 A2 A3 A4 A5

I try to do some loop to reduce repetition of the same code but fail.

2 Undefined index for checkbox.

I do some checkbox and i got error : undefined index if i submit the form with some of the checkbox not checked. I google but i dont know how to alter my coding with their solution because i do not understand their solution.

Below is my coding.

    <html>

<?php

    $connect = mysql_connect("localhost","root","") or die ("Coulnt connect!");
    mysql_select_db("book") or die ("Couldnt find db");

    $A1 = 'enable';
    $A2 = 'enable';
    $A3 = 'enable';
    $A4 = 'enable';
    $A5 = 'enable';

    $query = mysql_query("SELECT * FROM seats WHERE Seat_Number = 1 AND Alphabet = 'A'");
    $row = mysql_fetch_array($query);
    $check = $row['Availability'];

    if($check >0)
    {
        $A1 = 'disabled';
    }

    $query = mysql_query("SELECT * FROM seats WHERE Seat_Number = 2 AND Alphabet = 'A'");
    $row = mysql_fetch_array($query);
    $check = $row['Availability'];

        if($check >0)
    {
        $A2 = 'disabled';
    }


    $query = mysql_query("SELECT * FROM seats WHERE Seat_Number = 3 AND Alphabet = 'A'");
    $row = mysql_fetch_array($query);
    $check = $row['Availability'];

    if($check >0)
    {
        $A3 = 'disabled';
    }

        $query = mysql_query("SELECT * FROM seats WHERE Seat_Number = 4 AND Alphabet = 'A'");
    $row = mysql_fetch_array($query);
    $check = $row['Availability'];

    if($check >0)
    {
        $A4 = 'disabled';
    }

    $query = mysql_query("SELECT * FROM seats WHERE Seat_Number = 5 AND Alphabet = 'A'");
    $row = mysql_fetch_array($query);
    $check = $row['Availability'];

    if($check >0)
    {
        $A5 = 'disabled';
    }


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

        $ch1 = $_POST["ch1"];
        $ch2 = $_POST["ch2"];
        $ch3 = $_POST["ch3"];
        $ch4 = $_POST["ch4"];
        $ch5 = $_POST["ch5"];


        if(isset($_POST['ch1'])) 
        {
            echo 'You have select ch1';
            mysql_query("UPDATE seats SET Availability = 1 WHERE Alphabet = 'A' AND Seat_Number = 1");
        }

        if(isset($_POST['ch2'])) 
        {
            echo 'You have select ch2 <br>';
            mysql_query("UPDATE seats SET Availability = 1 WHERE Alphabet = 'A' AND Seat_Number = 2");
        }

        if(isset($_POST['ch3'])) 
        {
            echo 'You have select ch3 <br>';
            mysql_query("UPDATE seats SET Availability = 1 WHERE Alphabet = 'A' AND Seat_Number = 3");
        }

        if(isset($_POST['ch4'])) 
        {
            echo 'You have select ch4 <br>';
            mysql_query("UPDATE seats SET Availability = 1 WHERE Alphabet = 'A' AND Seat_Number = 4");
        }

        if(isset($_POST['ch5'])) 
        {
            echo 'You have select ch5 <br>';
            mysql_query("UPDATE seats SET Availability = 1 WHERE Alphabet = 'A' AND Seat_Number = 5");
        }

        }

?>

<center>
<body>

<form method="post" >

  <p>

    <input name="ch1" type="checkbox" id="A1" value="A1"<?php echo $A1; ?>/>
    <input name="ch2" type="checkbox" id="A2" value="A2"<?php echo $A2; ?>/>
    <input name="ch3" type="checkbox" id="A3" value="A3"<?php echo $A3; ?>/>
    <input name="ch4" type="checkbox" id="A4" value="A4"<?php echo $A4; ?>/>
    <input name="ch5" type="checkbox" id="A5" value="A5"<?php echo $A5; ?>/>


 </p>

<input type='submit' name='submit' value='Book Selected !' />
<input name="none" type="reset" value="Clear">

</form>
</body>
</center>
</html>

2012-04-05 15:43
by Irwan

im learning everything from w3school - bad idea!DaveRandom 2012-04-05 15:44

@DaveRandom It's really not so bad for starting off - 472084 2012-04-05 15:44

@Jleagle Teaching bad habits to a beginner propagates bad habits through to non-beginners. Start as you mean to go on - DaveRandom 2012-04-05 15:45

does it give a line number - encodes 2012-04-05 15:46

Side note: If you're copying / pasting code over and over and changing 2-3 characters, it can be accomplished in much less - Blake 2012-04-05 15:49

the error : undefined index is come from the checkbox that not checked when submit. So as DaveRandom suggest remove the code solve the error. Now can someone help me with the loop? Its tedious to repeat the same code if i have 50 seats - Irwan 2012-04-05 15:58

@Irwan That would be in the scope of another question. If this one was answered, mark it as the answer and ask another - Blake 2012-04-05 16:00

@Blake ok i will make another thread then : - Irwan 2012-04-05 16:07

here is some help with loops and functions:

    $A1 = 'enable';
    $A2 = 'enable';
    $A3 = 'enable';
    $A4 = 'enable';
    $A5 = 'enable';

    $seats = array(1,2,3,4,5);

    function check_availability($seat)
    {
        $query = mysql_query("SELECT * FROM seats WHERE Seat_Number = $seat AND Alphabet = 'A'");
        $row = mysql_fetch_array($query);
        $check = $row['Availability'];

        if($check >0)
        {
            return 'disabled';
        }
        else{
            return 'available';
        }

    }

what this function does is checking a seat for you and returning disabled or available correspondingly. and here is how we can call it:

foreach($seats as $seat){
         ${'A'.$seat} = check_availability($seat);
    }

this code assigns returned value from function to $A1, $A2, etc... and here is loop for POST:

if(isset($_POST ['submit']))
    {
        for($e=1 ; $e <=5 ; $e++){
            if(isset($_POST['ch'.$e])) 
            {
                echo 'You have select ch'.$e;
                mysql_query("UPDATE seats SET Availability = 1 WHERE Alphabet = 'A' AND Seat_Number = $e");
            }

        }
    }

basically we repeat checking isset() 5 times - var $e starts from being 1, then compairs if it's still less or equal to 5, if not increases by 1

at the same time we using $e to change seat number in mysql query.

2012-04-05 16:08
by Elen

Ok thanks for the code. I test it and it worked. I know that $seats = array(1,2,3,4,5); is to create array for the loop process. But i do not understand the use of variable $seat. Can explain a bit like where the $seat take value from and why use $seat instead of $seats - Irwan 2012-04-05 16:22

for check_availability() function - it don't matter how you call it, we could call it $w, it's purely for code readability. however in foreach loop $seat is 1 item from array $seats, again i could've call it $b. you would probably want to read manul for foreach to understand it better http://php.net/manual/en/control-structures.foreach.ph - Elen 2012-04-05 16:26

Ok thank you for the manual i will read it after this. Thank you all for the code given. Very Appreciated it. : - Irwan 2012-04-05 16:38

All you need to do to remove the errors is remove this block:

    $ch1 = $_POST["ch1"];
    $ch2 = $_POST["ch2"];
    $ch3 = $_POST["ch3"];
    $ch4 = $_POST["ch4"];
    $ch5 = $_POST["ch5"];

It doesn't do anything useful anyway - you never use the variables $ch1 etc anywhere in your code.

If you did want to keep the variables, you would move the individual lines to the relevant if (isset()) blocks - if you do this, you won;t try and use the $_POST keys before you have checked if they were set.

2012-04-05 15:47
by DaveRandom

assign the value to $ch1 is nicer when doing validation/stripping etc, firstly you don;t get lots of _POST[''] all over the page, secondly accessing a post variable is slower than accessing a variable directly (although that wouldn't be an issue in this example - encodes 2012-04-05 15:51

@encodes accessing a post variable is slower sounds like premature optimisation to me. Although I take your point - DaveRandom 2012-04-05 15:53

Source for: accessing a post variable is slower than accessing a variable directly - Blake 2012-04-05 15:53

@Blake I suspect that is true, since it is array access which definitely is slower (on a large scale, such as very multidimensional arrays) but only very slightly, so slightly it is irrelevant. Although even that is just conjecture - DaveRandom 2012-04-05 15:55

Ill try remove the code and thats solve the problem for the error came out (undefined index - Irwan 2012-04-05 15:55

@DaveRandom I'm all for php optimization that makes sense, ie: http://www.phpbench.com (My favorite section is the loops) -- but more for human readability. Me trying to figure out what the hell someone is referencing takes much more time than the 2 nanoseconds for the computer to eval it. Code for humans to read it, then optimize for computer resources. Not the other way around - Blake 2012-04-05 15:57

@Blake I whole-heartedly agree - DaveRandom 2012-04-05 15:58

agree with you 100% @DaveRandom, (re code for humans), again though it is much easier to read something like if($ch1 >5 && $ch3 >3 && ch4 ==1) rather than if($_POST['ch1'] >5 .. - encodes 2012-04-05 16:06

i think the issue is that you check for a post variable, you need to put it into an isset or something similiar

e.g. $ch1 = null; if(isset($_POST['ch1']){ $ch1 = $_POST['ch1']; }

that way it won't try and access the ch1 part of the array if its not set throwing an undefined index exception. Hope the explanation also helps to see where you went wrong.

you'd need to do for each _POST

2012-04-05 15:49
by encodes

Thanks for the reply but this is the most code i found while google. But unfortunately i do not understand it because im to newbie in php and i dont know how to alter my coding with this code - Irwan 2012-04-05 16:09

ok what you are doing in $ch1 = $POST['ch1'] is taking the value from the POST variable (basically an array of variables from a form), if you try and access an element of an array that doesn't exists then it will cause an error. if ch1 isn't posted $POST['ch1'] is not set and therefore throws an errro, what you need to do is check if the post variable is set, then if it is assign it to your local variable. php has a function called isset for this, you simply do if(isset($_POST['ch1']){ /code */} if ch1 isnt set it wont run the /code */ bit therefore avoiding the erro - encodes 2012-04-05 16:14

http://php.net/manual/en/function.isset.ph - encodes 2012-04-05 16:14

Undefined index for checkbox can be eleminated by simply using

$ch1 = isset($_POST["ch1"])?$_POST['ch1']:null;
$ch2 = isset($_POST["ch2"])?$_POST['ch2']:null;
$ch3 = isset($_POST["ch3"])?$_POST['ch3']:null;
$ch4 = isset($_POST["ch4"])?$_POST['ch4']:null;
$ch5 = isset($_POST["ch5"])?$_POST['ch5']:null;

instead of using

$ch1 = $_POST["ch1"];
$ch2 = $_POST["ch2"];
$ch3 = $_POST["ch3"];
$ch4 = $_POST["ch4"];
$ch5 = $_POST["ch5"];

For your next query about loop, you can use

<?php
$A[1] = 'enable';
$A[2] = 'enable';
$A[3] = 'enable';
$A[4] = 'enable';
$A[5] = 'enable';
for ($i=1, $i<=5, $i++) {
 $query = mysql_query("SELECT * FROM seats WHERE Seat_Number = ". $i ." AND Alphabet = 'A'");
 $row = mysql_fetch_array($query);
 $check = $row['Availability'];

    if($check >0)
    {
        $A[$i] = 'disabled';
    }
}
?>

2012-04-05 16:30
by Subho Halder