condition on submit

if i want to make a condition on clicking on submit button in a form, how can i do it in php?
for example if i have a page where the user have to login using his username and password saved already in a database (MySQL), i want to realize the condition that its username and password are just right like in the database. I have tried the condition if ($submit) but it didn't worked (i don't know why because i have seen some tutorials using this condition).
I am working on PHP version 4.2.1 and MySQL.

How can I do it?
Is this version of PHP different?
htannouryAsked:
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andreifConnect With a Mentor Commented:
You can us the same page, but form action should be directed to the page itself, not to another one
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andreifCommented:
if you want to use $submit variable, you should ensure that submit control's name us "submit":

<input type="submit" name="submit" value=" Click! ">
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htannouryAuthor Commented:
i have tried this but it didn't worked
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andreifCommented:
in this case problem can be in "Register Globals" switched off mode. In this case $submit variable is not defined.

For PHP 4.2+ use
$_GET["submit"] or $_POST["submit"] (depends on form method)
variables

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andreifCommented:
more information about predefined variables

http://www.php.net/manual/en/language.variables.predefined.php
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htannouryAuthor Commented:
In the form (method="post") that i use i have written the submit input like this:
<input type="submit" name="submit" value="click">
in the form i have a field of name "first"

and the condition is written here:
<?
$submit=$_POST['submit'];
echo "<br>";

echo "submit is $submit";
echo "<br>";
 
if($submit == "click")
     {
     if ($first == "")
          {echo "you have to type your first name";}
          else
          {echo " thank you for your first name";
               }
     }
     else
     {
     echo "you have to click on submit";
     }
?>

i always obtained the notice: undefined index submit.
do you expect that there is something missing in the configuration of the php? what i have to do?

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andreifCommented:
try to print out $_POST array in the beginning of the script

print_r($_POST);
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htannouryAuthor Commented:
I have used $_POST in the second file (action of the form)
and i used the condition that i have written so it worked. Thank you about your cooperation, but is there a way to let this condition work in the same file?
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andreifCommented:
In this case condition should be more complex.

What does your script do with the form data?
Does it checks username/password in database?
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htannouryAuthor Commented:
Yes it is for checking the username and password.
Is it necessary to have a new page where the condition should be written?
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No comment has been added lately, so it's time to clean up this TA.
I will leave a recommendation in the Cleanup topic area that this question is:
Accept: andreif
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