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I have a form and I'm doing input validation, so when the user inputs something wrong I generate an error message and refill all the fields the user entered.

Now, some errors popped up when I started using the php.ini file for mysql stuff, such as

Undefined index: var in file.php on line n

For a simple text input (a title) I was able to fix this fairly easily, by doing

value="<?= isset($_POST["title"]) ? $_POST["title"] : "";?>"

However, I'm also using 5 radio buttons to give a rating, like this:

value="1" <?= $_POST["grade"] == "1" ? "checked" : "" ?>
value="2" <?= $_POST["grade"] == "2" ? "checked" : "" ?>
etc

I tried applying the isset bandage here as well,

value="1" <?= isset($_POST["grade"] == "1") ? "checked" : "" ?>

but as I was quickly reminded, isset only works with variables and arrays, not booleans.

What would be an appropriate way to solve this?

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  • Could you please try replace the <?= with <?php and try again? Commented Oct 21, 2020 at 10:45
  • who told that isset doesn't work for boolean? Commented Oct 21, 2020 at 10:45
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    @MerianosNikos If they replace <?= with <?php, it won't output anything. <?= is just a shorter way of writing <?php echo Commented Oct 21, 2020 at 10:46
  • @MagnusEriksson I just thought that maybe changed something in the php.ini that affects the short opening tags. Without a full code example, it's not that easy to help. Commented Oct 21, 2020 at 10:47
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    @MerianosNikos - The shorthand <?= is available regardless of the short open tags setting. Commented Oct 21, 2020 at 10:48

1 Answer 1

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The first thing you have to do is check whether the variable is set or not. Then you can append your comparison with an operator.

value="1" <?= isset($_POST["grade"]) && $_POST["grade"] == "1" ? "checked" : "" ?>
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2 Comments

That does indeed work, thank you! I attempted something similar before but I must have gotten the syntax or order wrong.
@Robin you are frequently answering question, but I am not noticing a lot closing. Please understand that after 10 years of feverish Q&A, all basic php questions are duplicates. Please vote to close duplicate questions.

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