Loops and Arrays

dkintheuk · January 3rd, 2004, 07:52 PM

Hi all,

Can anyone tell me why i'm getting the following problem?

I've typed in the code for the dynamic.html, dynamic.php and dynamic2.php example in Beginning PHP4 - chapter 5.

I'm getting the following error when i go from dynamic.php to dynamic2.php...

Notice: Undefined offset: 1 in c:\inetpub\wwwroot\php\dynamic2.php on line 14

Notice: Undefined offset: 1 in c:\inetpub\wwwroot\php\dynamic2.php on line 15

Line 14 and 15 are:

echo" $Child[$Count]";
$CheckEmpty = "$Child[$Count]";

It seems that the code gets to the final array item, moves to the next one and the check for empty actually results in an error as there is no array item to be found at all rather than it being set to blank...

I'm confused by this. Any good ideas out there?

Rob.

richard.york · January 3rd, 2004, 08:26 PM

This is a horrible demostration of a do while loop.

In a nutshell you are getting these errors because of poorly written code. Notice level errors of undefined... something or another always means that a variable did not exist before you attempted to use it in a context like outputting it or comparing it. PHP automatically creates a copy of the variable in memory with null value temporarily if it doesn't exist... and then will complain in the form of a Notice level error.

For your reading pleasure:
http://www.php.net/isset
http://www.php.net/empty

These constructs will assist you in writing more explicit code and enable you to avoid the Notice level errors.

Here is a better demonstration of what the book is trying to accomplish:

Code:

<html>
    <head>
        <title>dynamic.html</title>
    </head>
    <body>
        <form method='post' action='dynamic.php'>
            How many children do you have? 
                 <input type='text' name='number' />
                <input type='submit' name='action' value='Continue' />
        </form>
    </body>
</html>

// dynamic.php

<html>
    <head>
        <title>dynamic.php</title>
    </head>
    <body>
        <form method='post' action='dynamic2.php'>
        <?php

            for ($i = 1; $i <= $_POST["number"]; $i++)
            {
                echo "Please enter the name of child {$i}:";
                echo "<input type='text' name='child[]' /><br />";
            }

            echo "<input type='submit' name='action' value='Continue' />";

        ?>
        </form>
    </body>
</html>
<html>
    <head>
        <title>dynamic2.php</title>
    </head>
    <body>
        Your children's name's are:<br />
        <?php

            for ($i = 0; $i < count($_POST["child"]); $i++)
            {
                if (!empty($_POST["child"][$i]))
                {
                    $_POST["child"][$i]."<br />";
                }

                else
                {
                    echo "You did not enter child #".($i+1)."'s name";
                }
            }

        ?>
    </body>
</html>

Hopefully that makes a little more sense? Please ask if you don't understand something! The book uses twice as much code as is really neccessary. And the do while loop that they use is actually the worst way to do that.

: )
Rich

:::::::::::::::::::::::::::::::::
Smiling Souls
http://www.smilingsouls.net
:::::::::::::::::::::::::::::::::

richard.york · January 3rd, 2004, 08:36 PM

Just for kicks.. this is an even better approach to 2 and 3:

// dynamic.php

if (isset($_POST["number"]) && is_numeric($_POST["number"]))
{
 for ($i = 1; $i <= $_POST["number"]; $i++)
 {
 echo "Please enter the name of child {$i}:";
 echo "<input type='text' name='child[]' /> ";
 }
}

else
{
 echo "Error: you did not enter a valid number!";
}

http://www.php.net/is_numeric
The use of this function ensures that the data provided is a number. isset ensures that it exists, without isset if the variable did not exist you would get a notice level error.

// dynamic2.php

if (isset($_POST["child"]) && is_array($_POST["child"]))
{
 for ($i = 0; $i < count($_POST["child"]); $i++)
 {
 if (!empty($_POST["child"][$i]))
 {
 $_POST["child"][$i]." ";
 }

 else
 {
 echo "You did not enter child #".($i+1)."'s name";
 }
 }
}

else
{
 echo "You did not enter any of your children's names";
}

http://www.php.net/is_array
The use of is_array ensures that the variable is an array.

I am also using register_globals = off, which is why I use the $_POST superglobal array. Hundreds, if not thousands of posts on this topic in p2p alone.

: )
Rich

:::::::::::::::::::::::::::::::::
Smiling Souls
http://www.smilingsouls.net
:::::::::::::::::::::::::::::::::

dkintheuk · January 4th, 2004, 06:40 PM

Thanks and thanks and thanks again... totally clear now and quite infuriating that the examples in the books have now caused so many problems already for me that i've needed to decipher.

The thing about $_POST is clear and i discovered that one a while ago but thanks for the explanation of how i might like to use it.

I'm just trying to become clear enough that i can set myself a task to design some tool for a purpose and then learn as i go...

Wish me luck!

Rob.

nikolai · January 5th, 2004, 05:58 PM

The real reason this is a problem is because the default configuration settings of PHP versions earlier than 4.2.0 suppressed NOTICE level warnings, so many programmers thought that the above "bad" code was, in fact, "clever".

Sigh.

Take care,

Nik
http://www.bigaction.org/

fjace · September 12th, 2005, 10:50 PM

Any help would be apprciated. I am have notices from the index I am using for the arrays. The code is below

<?php
 if ($teaches > 0){
 $eteachdata = explode(",", $teachdata);
 $estartdata = explode(",", $startdata);
 $eenddata = explode(",", $enddata);
 $mark = count($eteachdata);
 if ($mark > 0) {
 echo "<table width=\"600\" border=\"0\"><tr><td>Teacher</td><td>Start</td><td>End</td><td>Total</td></tr>";
 for($i = 0; $i <= $mark; $i++){
 line 233 $id = $eteachdata[$i];
 $sqldata = "SELECT * FROM `teachers` WHERE `id` = '$id'";
 $result = mysql_query($sqldata);
 $row = mysql_fetch_array($result);
 $teacher = "{$row["firstName"]} {$row["lastName"]}";
 line 238 $total = $eenddata[$i]-$estartdata[$i];
 line 239 echo "<tr><td>{$teacher}</td><td>{$estartdata[$i]}</td><td>{$eenddata[$i]}</td><td>{$total}</td></tr>";
 }
 }
 }
 else{
 echo"<table width=\"300\" border=\"0\"><tr><td>No items books have been sorted yet.</td></tr></table>";
 }
 ?>

Here are the errors I am getting.

Notice: Undefined offset: 1 in c:\program files\easyphp\www\negaard\inventory.php on line 233

Notice: Undefined offset: 1 in c:\program files\easyphp\www\negaard\inventory.php on line 238

Notice: Undefined offset: 1 in c:\program files\easyphp\www\negaard\inventory.php on line 238

Notice: Undefined offset: 1 in c:\program files\easyphp\www\negaard\inventory.php on line 239

Notice: Undefined offset: 1 in c:\program files\easyphp\www\negaard\inventory.php on line 239

For now I can hide the errors but any good programmer should try and correct them right? Please help as soon as anyone can. Thanks in advanced.

fjace · September 12th, 2005, 11:38 PM

Actually forget that I even posted that and I am sorry that I took up the digital space. I am a nut and realized that it was only doing that because I had "<=" it my for loop instead of "<". It works beautifully now.

Sorry