can't compare a blank var with a blank $_POST var

[charmquark]

I'm having a problem comparing blank variables (form inputs which should remain blank)

[code]
$coef1 = "";
$coef2 = "";
$coef3 = "2";


function check($pqnum){


  if ((!$_POST['coef3']==$coef1)
|| (!$_POST['coef2']==$coef2)
|| (!$_POST['coef3']==$coef3)
)
{
      return FALSE;
    }
    else {
      return TRUE;
    }
}[/code]


Any ideas how I can fix this so if the $coef is " " then the if statement works?

[dgiberson]

if (isset($_POST['coef'])){
echo "variable is set";
}else{
echo "variable is not set";
}

[charmquark]

Thanks, but I still don't get it and I'm getting parse errors.
What if I was to change the definition of the $coef  to a $_POST['coef'] =""; ?

[dgiberson]

if (isset($_POST['coef']) {
  if ($_POST['coef'] == $coef) {
  //do something
  }
}

[emehrkay]

print_r($_POST) to see what vars you have available to you

[charmquark]

[quote author=dgiberson link=topic=122737.msg506598#msg506598 date=1169002126]
if (isset($_POST['coef']) {
  if ($_POST['coef'] == $coef) {
  //do something
  }
}
[/quote]

It makes sense to use the isset(), but I'm still confused (still getting parse errors) when checking for all 4 variables as in my above example.  For this question, 3 of the variables should remain blank.  For other questions one or two or none of the variables may be blank.

I tried
print_r($_POST) ;
This was the output:: Array ( [coef1] => [coef2] => [coef3] => [coef4] => 2 [submit] => submit [qnum] => 3 )
Makes sense, but I'm tripping over these blank defined variables when comparing them to the posted variables.

Interesting note:  Other chemistry exercises I wrote don't have any problem with blank coefficients, but I'm pulling the blank variables from a database table.  In this exercise, I'm just using different pages for each question as the form construction is different, depending on the question.


I think I might retry putting the answers and form type in a database table, and then use a case statement to call the type of form... although I'd still like to know how to compare a blank $_POST var with a blank defined variable.

[kenrbnsn]

Going back to the code you originally posted, the "if" statement is incorrect and the variables will not be defined inside the function. Try this instead:
[code]<?php

function check($pqnum){

  $coef1 = "";
  $coef2 = "";
  $coef3 = "2";
  if (($_POST['coef3'] != $coef1)
|| ($_POST['coef2'] != $coef2)
|| ($_POST['coef3'] != $coef3))
{
      return FALSE;
    }
    else {
      return TRUE;
    }
}
?>[/code]

Ken

[charmquark]

;D  kenrbnsn, the solution is all good ... it works great and reduces confusion.
Of course, my variable scope was all wrong,  I'm only a copy and paste php wannabe.  Now it works exactly as I expect.  hugs....

More thinking about this script requires a change of the structure.  There are 25 files. <egads>  Last night I created the table in the db with a column called type.  I'm only guessing, but the next step is to get my head around the switch() ??? 

Each $pqnum (question number) has a form type, either synthesis, decomp or other.

Does the following make sense?
[code]

wannabe code:


query($qnum=$pqnum);
query($type);
switch() {
case if $type="synthesis":
echo $show_form_synth;
break;
case if $type="decomp":
echo $show_form_decomp;
break;
case if $type="other":
echo show_form_other;
break;
}[/code]

Thanks again for helping. 

[kenrbnsn]

You really should read up on the syntax of the [url=http://www.php.net/manual/en/control-structures.switch.php]switch statement[/url]

[code]<?php
switch($type) {
    case "synthesis":
        echo $show_form_synth;
        break;
    case "decomp":
        echo $show_form_decomp;
        break;
    case if "other":
        echo show_form_other;
        break;
}
?>[/code]

Also, learn to indent your code, it will make reading and debugging much easier.

Ken

[charmquark]

Again, you are absolutely right.  For now, I'm the only person looking at this and it's all fresh in my head. If I ever hope to share this application with another chemistry teacher, I need to pull up my indentation socks.  I've googled php indentation, but feel free to point me to your favorite reference.


I've yet to create a script of my own with a switch (),  if always worked.  Just fitting the switch into the flow of the script is hard for me, so please be patient.
I'll go away and think/read about it and play with it some more.

Thanks again for your help and to everyones response.

Have a happy php freaking day.

[anatak]

[quote]
Interesting note:  Other chemistry exercises I wrote don't have any problem with blank coefficients, but I'm pulling the blank variables from a database table.  In this exercise, I'm just using different pages for each question as the form construction is different, depending on the question.
[/quote]

there is a difference between "" and null out of a database.
check if in your database you have the "" string or the null variable.