naming a dynamic number of form inputs incrementally - php

Question

I generate a dynamic quantity of form inputs, based on a user-submitted number ($transponum).
I use str_repeat to build a string containing the desired number of inputs.
But I'm having trouble naming the inputs. I need:
<input type="text" name="transpo(a number that increases every repeat)" />
How can I achieve that with PHP?
Here is my code:
<form id="form" name="form" method="post" action="step8.php" role="form">
<div class="form-group"><?php
$a = 1;
$str.= "<label class=\"control-label\" for=\"exampleInputEmail1\">Name</label>";
$str.= "<input style=\"width: 60%;\" type=\"text\" class=\"form-control\" id=\"transponum\" name=\"transponame".$a."\" placeholder=\"Name\">";
$str.= "<label class=\"control-label\" for=\"exampleInputEmail1\">ID</label>";
$str.= "<input style=\"width: 60%;\" type=\"text\" class=\"form-control\" id=\"transponum\" name=\"transpoid".$a."\" placeholder=\"Name\"><hr>";
$str.= $a = $a+1;
echo str_repeat($str, $transponum);
?></div>
<button type="submit" class="btn-success btn" name="submit">Next</button>
</form>

Answer 1

I have several suggestions, detailed below:
Use a loop
Use a for loop rather than str_repeat.
Use the loop to increment your $a variable from 1 to $transponum.
for ($a=1;$a<=$transponum;$a++) { ... }
Post as arrays
Name your inputs so that they post as arrays. That way, you don't need to dynamically build the input names.
<input name="names[]" />
<input name="ids[]" />
Notice the square brackets after the variable name, that's what makes it an array. You can group the elements into different arrays by assigning the same name to different elements.
-- FAQ # php.net
Then, you'll end up with a $_POST array like this:
Array
(
[names] => Array
(
[0] => 'name 1',
[1] => 'name 2',
[2] => 'name 3',
...
),
[ids] => Array
(
[0] => 'id 1',
[1] => 'id 2',
[2] => 'id 3',
...
)
)
Remove duplicated IDs
Element IDs must be unique. Associate labels with inputs implicitly by placing the <input> elements inside their respective <label> elements. Then you can remove the duplicated IDs.
To associate a label with another control implicitly, the control element must be within the contents of the LABEL element. -- forms # w3.org
<label>Name: <input /></label>
Also see this simple label example at developer.mozilla.org, for reference.
Complete Example
Here's an example that includes all of my suggestions:
<form id="form" name="form" method="post" action="step8.php" role="form">
<div class="form-group"> <?php
for ($a=1;$a<=$transponum;$a++) {
?><label>
<span>Name</span>
<input type="text" name="transponame[<?=$a?>]" placeholder="Name">
</label>
<label>
<span>ID</span>
<input type="text" name="transpoid[<?=$a?>]" placeholder="Name">
</label>
<hr><?php
}
?></div>
<button type="submit" class="btn-success btn" name="submit">Next</button>
</form>
Edit:
Note that specifying the $a value in input names is probably not necessary. In your context, empty brackets will work just as well:
<input type="text" name="transponame[]" placeholder="Name">
Specifying array keys is optional in HTML. If you do not specify the keys, the array gets filled in the order the elements appear in the form. -- FAQ # php.net

Answer 2

To add to showdev's answer.
You cannot use str_repeat to achieve what you have in mind. str_repeat literally repeats a string. See the documentation page.
In your case, you have to use either a loop or create array type input names.

Answer 3

Make sure you don't use duplicate Ids
<form id="form" name="form" method="post" action="step8.php" role="form">
<div class="form-group">
<?php for($i=0;$i<transponum;$i++){ ?>
<label class="control-label" for="exampleInputEmail1">Name</label>";
<input style="width: 60%;" type="text" class="form-control" id="transponum" name="transponame<?php echo $i;?>" placeholder="Name">
<label class="control-label" for="exampleInputEmail1">ID</label>
<input style="width: 60%;" type="text" class="form-control" id="transponumLabel" name="transpoid<?php echo $i;?>" placeholder="Name"><hr>
<?php } ?>
</div>
<button type="submit" class="btn-success btn" name="submit">Next</button>
</form>