php sum values of form check boxes when checked

Question

I have a form in php that displays checkboxes. These checkboxes are associated with a numerical value populated from mysql. What I'm looking to do is add the values of each checkbox, but only if the box is checked.

The problem I am running into is no matter which boxes I have checked, the value from the first checkbox(es) are returned. For example, if there are 5 total checkboxes and I select the bottom 2, the returned sum is for the 2 top boxes not the bottom boxes. It seems my php code knows boxes are being checked, but just doesn't know which boxes are being checked.

Here is my form code

echo "<input type=\"hidden\" name=\"ID[]\" value=\"".$row['ID']."\" />";
echo "<tr><td>&nbsp;<input type=\"checkbox\" name=\"checked[]\" value=\"Y\"></td>";
echo "<input type=\"hidden\" name=\"amount[]\" value=\"".$row['amount']."\" />";

and here is my post

if('POST' == $_SERVER['REQUEST_METHOD']) {
$amt = 0;
$totamt = 0;
foreach($_POST['ID'] as $i => $id)
{

$id = mysql_real_escape_string($id);
  $checked = mysql_real_escape_string($_POST['checked'][$i]);
  $amt = mysql_real_escape_string($_POST['amount'][$i]);

if ($checked == "Y") {
$totamt = $totamt + $amt;
$amt = 0;
}

}
echo $totamt;
}

Thank you for your help.

You probably need JavaScript's onclick or onchange events to change the attributes of your input elements. — void
Couple of things to check: is the amount field different for every row (check the HTML output). Check the output of print_r($_POST). What are you seeing there. Maybe there's something happening that you're not seeing. — Robbert

Barmar Barmar · Accepted Answer · 2013-04-04T23:52:31

The only checkboxes that are sent from the form are the ones that are checked, and the array indexes will start from 0 no matter which ones they are. So there's no correspondence between the indexes of the checkboxes and the indexes of the hidden fields. There are a few ways to deal with this.

One way is to put explicit indexes in the checkbox names:

echo "<tr><td>&nbsp;<input type=\"checkbox\" name=\"checked[".$row['ID']."]\" value=\"Y\"></td>";
echo "<input type=\"hidden\" name=\"amount[".$row['ID']."]\" value=\"".$row['amount']."\" />";

Then you can add up:

$totamt += $_POST['amount'][$_POST['checked'][$i]];

Another way is to put the amounts directly in the value of the checkboxes, instead of the useless Y value:

echo "<tr><td>&nbsp;<input type=\"checkbox\" name=\"checked[]\" value=\"".$row['amount']."\" /></td>";

Then you do:

$totamt += $_POST['checked'][$i];

A third way is to put explicit indexes in the names of all the fields, instead of letting PHP assign them when the form is submitted:

echo "<input type=\"hidden\" name=\"ID[".$i."]\" value=\"".$row['ID']."\" />";
echo "<tr><td>&nbsp;<input type=\"checkbox\" name=\"checked[".$i."]\" value=\"Y\"></td>";
echo "<input type=\"hidden\" name=\"amount[".$i."]\" value=\"".$row['amount']."\" />";

where $i is a variable that you increment as you're generating the form. This will make the indexes work the way your form code expects.

php sum values of form check boxes when checked

3 Answers