How to sum value from database and input value in textbox - php

Question

here is my problem: I get the value of STOCK from the database and I input a value in textbox, the problem is that when I try to compute the system does not recognized or say undefined index: stock
here is the syntax from value to computation:
<td><input type = "text" name = "stock[]" size = "5" value = '<?php echo $row['stock']; ?>' disabled></td>
<td><input type = 'text' name = 'stockin[]' size = '5'></td>
<td><input type ="submit" name = "btn" value = "re-stock"></td>
here is the syntax for computation which I place after the tag
<?php
$capture_field_vals1="";
if(isset($_POST['btn']))
{
foreach($_POST['stockin'] as $key => $text_field){
$capture_field_vals1 .= $text_field;
}
echo $capture_field_vals1;
$num1 = $_POST['stock[]'];
$num2 = $_POST['$capture_field_vals1'];
$num3 = $num1 + $num2;
echo $num3;
}
?>

Answer 1

"[]" means array, at this point you might need to write more than one data to the database. Also in the PHP script, you could observe incoming post by var_dump($_POST);
<?php
if( isset($_POST["stock"]) ){
foreach ($_POST["stock"] as $key => $value) {
echo $value."<BR>";
}
}
?>
<form method="post" action="?">
<input type = "text" name = "stock[]" size = "5" value = '1'/>
<input type = "text" name = "stock[]" size = "5" value = '2'/>
<input type="submit">
</form>