PHP $_GET from a form undefined array error

Question

I'm currently learning PHP from the very basic and started following a 2 year old youtube video. I'm trying to make a simple php calculator based from his code, but I've run into an error despite copying 100% of the example code, I'm guessing this is due to the version difference. What can be done to fix this issue, error code says undefined array, does this mean that I just need to pre-define the variables? How would I do this.

    <!DOCTYPE html>
<html lang="en" dir="ltr">
  <head>
    <meta charset="utf-8">
    <title></title>
  </head>
  <body>

    <form action="site.php" method="get">
      <input type="number" name="num1">
      <br>
      <input type="number" name="num2">
      <br>
      <input type="submit">
    </form>

  Answer: <?php echo $_GET["num1"] + $_GET["num2"] ?>

  </body>
</html>

@RGriffiths yes, that's the exact code he was using as an example, and it was working in his video. use dot like this? Answer: <?php echo $_GET["num1"] . $_GET["num2"] ?> it gives the same error — Hero Stradivari
– Hero Stradivari, Commented Jan 8, 2021 at 21:36
Forget the dot thing. name = "num1", name = "num2" you have missed the equals — RGriffiths
– RGriffiths, Commented Jan 8, 2021 at 21:41
@RGriffiths Hi thank you very much for pointing that out, I did miss the = and that was very dumb of me. The code is working now, but the error still persist. ERROR: Warning: Undefined array key "num1" in C:\Users\Kenji\www\site.php on line 17 — Hero Stradivari
– Hero Stradivari, Commented Jan 8, 2021 at 21:47
You're not checking to see if the form has been submitted. If it hasn't the $_GET array will be empty and you'll get the error you're seeing. The $_GET variables will only exist when the form is actually submitted. — Tangentially Perpendicular
– Tangentially Perpendicular, Commented Jan 8, 2021 at 21:58

Alexander Dobernig · Accepted Answer · 2021-01-08 22:47:15Z

1

Explanation:

In the past (old php versions) it was not necessary to define/declare variables. This has changed and now you will get warnings/notices.

If you call the page for the first time the variables num1 and num2 are not defined - that will result in that warning. Only when you enter them and send the form then they will have a value.

So insert a condition if that variables are empty and only if they are NOT empty make the calculation and print it.

! means NOT

isset() checks if the variable exists. https://www.php.net/manual/de/function.isset (empty was a wrong approach because 0 is a valid entry as one commenter pointed thankfully out)

 <!DOCTYPE html>
<html lang="en" dir="ltr">
  <head>
    <meta charset="utf-8">
    <title></title>
  </head>
  <body>

    <form action="site.php" method="get">
      <input type="number" name="num1">
      <br>
      <input type="number" name="num2">
      <br>
      <input type="submit">
    </form>

  Answer: <?php 

if ((!isset($_GET["num1"]) && (!isset($_GET["num1"])){ 
    echo $_GET["num1"] + $_GET["num2"]; 
}

?>

  </body>
</html>

edited Jan 8, 2021 at 22:47

answered Jan 8, 2021 at 21:57

Alexander Dobernig

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3 Comments

rickdenhaan Over a year ago

Warning: since you're dealing with inputs of type number, you might want to use isset() rather than !empty() (or a combination of both). empty($_GET["num1"]) will return true if the entered value is zero.

Alexander Dobernig Over a year ago

@rickdenhaan you are right - I never had the situation before that 0 may be a valid entry ;-) but yes 0+5 is a valid entry

Alexander Dobernig Over a year ago

@rickdenhaan i updated the answer to reflect your comment. thx.

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