Need help accessing POST data

[BenGoldberg]

So basically I'm using PHP to solve a math problem for me. The user puts in a few parameters and the program runs those numbers through the algorithm and spits out a bunch of xy coordinates. I'm using the PHP SELF method to retrieve the user input. This all works fine, but it's afterwords that I run into problems. I create a drop down menu of all the x values and I want the user to be able to choose any x value they wish and to have the corresponding y value be displayed. The problem is that I have to use another POST command for this and when I do, it wipes out all the computed data.  Of course the y-value is never displayed, and there lies the problem.

 

I'm sure there are many ways to get around this, but I could not find one out myself. Anyone have any ideas?

[anupamsaha]

Please provide the code here.

[BenGoldberg]

Alright, here's the important stuff. Don't get too caught up in the math, the important thing to know is my $a array are my x values and my $b array are my y values. I created the drop down menu of the x values at the end but there is no attempt on there of trying to display the y values. But basically if they choose $a[37] I would like $b[37] to be displayed.

 

<form action="<?php echo $_SERVER['PHP_SELF']; ?>" method="post">

<?php

function dydx($x,$y){

$equation = 3 * pow($x, 2);
return $equation;
}

?>

<table>
<tr>
	<td>Enter number of partitions:</td>
	<td><input type="text" size="7" maxlength="7" name="partitions" value="" /></td>
</tr>
<tr>
	<td>Enter initial x value, x(0):</td>
	<td><input type="text" size="3" maxlength="3" name="initialx" value="" /></td>
</tr>
<tr>
	<td>Enter the ending x value:</td>
	<td><input type="text" size="3" maxlength="3" name="endingx" value="" /></td>
</tr>
<tr>
	<td>Enter initial y value, y(0):</td>
	<td><input type="text" size="3" maxlength="3" name="initialy" value="" /></td>
</tr>
</table>

</br>

<input type="submit" name="runge kutta name" value="Run Program" />

</form>

<?php

$partitions = $_POST['partitions'];
$initialx = $_POST['initialx'];
$endingx = $_POST['endingx'];
$initialy = $_POST['initialy'];

if ($_POST['partitions'] != 0) {

$h = ($endingx - $initialx)/$partitions;
}


$a[1] = $initialx;
$b[1] = $initialy;

for ($i = 1; $i <= $partitions; $i++) {

$k1 = dydx($a[$i], $b[$i]);
$k2 = dydx($a[$i] + (1/2)*$h, $b[$i] + (1/2)*$h*$k1);
$k3 = dydx($a[$i] + (1/2)*$h, $b[$i] + (1/2)*$h*$k2);
$k4 = dydx($a[$i] + $h, $b[$i] + $h*$k3);

$a[$i + 1] = $a[$i] + $h;
$b[$i + 1] = $b[$i] + (1/6)*$h*($k1 + 2*$k2 + 2*$k3 + $k4);
}

for ($i = 1; $i <= $partitions + 1; $i++) {

$xyarray["$a[$i]"] = $b[$i];
}

$_SESSION['graph'] = $xyarray;

?>

</br></br>

Choose a partition of X:



<select name="output">

<?php

for ($i = 1; $i <= $partitions + 1; $i++) {

echo "<option value=\"$a[$i]\">$a[$i]</option>\n";
}

?>

[anupamsaha]

Seems you have missed to check whether the form is posted or not. Here is the code that I edited. Let us know if it works or not.

 

<form action="<?php echo $_SERVER['PHP_SELF']; ?>" method="post"><?php

function dydx($x,$y){

  $equation = 3 * pow($x, 2);
  return $equation;
}

?>

<table>
<tr>
	<td>Enter number of partitions:</td>
	<td><input type="text" size="7" maxlength="7" name="partitions"
		value="" /></td>
</tr>
<tr>
	<td>Enter initial x value, x(0):</td>
	<td><input type="text" size="3" maxlength="3" name="initialx" value="" /></td>
</tr>
<tr>
	<td>Enter the ending x value:</td>
	<td><input type="text" size="3" maxlength="3" name="endingx" value="" /></td>
</tr>
<tr>
	<td>Enter initial y value, y(0):</td>
	<td><input type="text" size="3" maxlength="3" name="initialy" value="" /></td>
</tr>
</table>

</br>

<input type="submit" name="runge kutta name" value="Run Program" />
<?php

if ($_SERVER['REQUEST_METHOD'] == 'POST' ) { // make sure that the form is posted

  $partitions = $_POST['partitions'];
  $initialx = $_POST['initialx'];
  $endingx = $_POST['endingx'];
  $initialy = $_POST['initialy'];

  if ($_POST['partitions'] != 0) {

    $h = ($endingx - $initialx)/$partitions;
  }


  $a[1] = $initialx;
  $b[1] = $initialy;

  for ($i = 1; $i <= $partitions; $i++) {

    $k1 = dydx($a[$i], $b[$i]);
    $k2 = dydx($a[$i] + (1/2)*$h, $b[$i] + (1/2)*$h*$k1);
    $k3 = dydx($a[$i] + (1/2)*$h, $b[$i] + (1/2)*$h*$k2);
    $k4 = dydx($a[$i] + $h, $b[$i] + $h*$k3);

    $a[$i + 1] = $a[$i] + $h;
    $b[$i + 1] = $b[$i] + (1/6)*$h*($k1 + 2*$k2 + 2*$k3 + $k4);
  }

  for ($i = 1; $i <= $partitions + 1; $i++) {

    $xyarray["$a[$i]"] = $b[$i];
  }

  $_SESSION['graph'] = $xyarray;

  ?>
  </br>
</br>

Choose a partition of X: <select name="output">

<?php

  for ($i = 1; $i <= $partitions + 1; $i++) {
  
    echo "<option value=\"$a[$i]\">$a[$i]</option>\n";
  }
} // if ($_SERVER['REQUEST_METHOD'] == 'POST' ) ends
?>
</form>

[BenGoldberg]

Ok so here's what I have now...

 

<form action="<?php echo $_SERVER['PHP_SELF']; ?>" method="post">

<table>
<tr>
	<td>Enter function y prime:</td>
	<td><input type="text" size="50" maxlength="" name="yprime" value="" /></td>
</tr>
<tr>
	<td>Enter number of partitions:</td>
	<td><input type="text" size="7" maxlength="7" name="partitions" value="" /></td>
</tr>
<tr>
	<td>Enter initial x value, x(0):</td>
	<td><input type="text" size="3" maxlength="3" name="initialx" value="" /></td>
</tr>
<tr>
	<td>Enter the ending x value:</td>
	<td><input type="text" size="3" maxlength="3" name="endingx" value="" /></td>
</tr>
<tr>
	<td>Enter initial y value, y(0):</td>
	<td><input type="text" size="3" maxlength="3" name="initialy" value="" /></td>
</tr>
</table>

</br>

<input type="submit" name="runge kutta name" value="Run Program" />

</form>

<?php

if ($_SERVER['REQUEST_METHOD'] == 'POST' ) { // make sure that the form is posted

$yprime = $_POST['yprime'];
$partitions = $_POST['partitions'];
$initialx = $_POST['initialx'];
$endingx = $_POST['endingx'];
$initialy = $_POST['initialy'];

function dydx($x,$y){

$equation = 2 * $x;
return $equation;
}

if ($_POST['partitions'] != 0) {

$h = ($endingx - $initialx)/$partitions;
}


$a[1] = $initialx;
$b[1] = $initialy;

for ($i = 1; $i <= $partitions; $i++) {

$k1 = dydx($a[$i], $b[$i]);
$k2 = dydx($a[$i] + (1/2)*$h, $b[$i] + (1/2)*$h*$k1);
$k3 = dydx($a[$i] + (1/2)*$h, $b[$i] + (1/2)*$h*$k2);
$k4 = dydx($a[$i] + $h, $b[$i] + $h*$k3);

$a[$i + 1] = $a[$i] + $h;
$b[$i + 1] = $b[$i] + (1/6)*$h*($k1 + 2*$k2 + 2*$k3 + $k4);
}

for ($i = 1; $i <= $partitions + 1; $i++) {

$xyarray["$a[$i]"] = $b[$i];
}

$_SESSION['graph'] = $xyarray;

} // if ($_SERVER['REQUEST_METHOD'] == 'POST' ) ends

?>

</br></br>

Choose a partition of X:

<form action="<?php echo $_SERVER['PHP_SELF']; ?>" method="post">

<select name="output">

<?php

for ($i = 1; $i <= $partitions + 1; $i++) {

echo "<option value=\"$b[$i]\">$a[$i]</option>\n";
}

?>

</select>

<input type="submit" name="runge kutta name" value="See Y" />

</form>



<?php

echo $_POST['output'];

 

I put in my second post command to display the y value for the corresponding x value, and it almost works. It successfully displays the value I expect it to but it wipes out all the data from the $a and $b arrays at the same time. I would like to preserve that data until new data is inputted for partitions, initial x, ending x, and initial y. This is where I'm having problems.

[anupamsaha]

Here you go

 

<table>
<tr>
	<td>Enter function y prime:</td>
	<td><input type="text" size="50" maxlength="" name="yprime" value="<?php echo (isset($_POST['yprime']) ? $_POST['yprime'] : '')?>" /></td>
</tr>
<tr>
	<td>Enter number of partitions:</td>
	<td><input type="text" size="7" maxlength="7" name="partitions" value="<?php echo (isset($_POST['partitions']) ? $_POST['partitions'] : '')?>" /></td>
</tr>
<tr>
	<td>Enter initial x value, x(0):</td>
	<td><input type="text" size="3" maxlength="3" name="initialx" value="<?php echo (isset($_POST['initialx']) ? $_POST['initialx'] : '')?>" /></td>
</tr>
<tr>
	<td>Enter the ending x value:</td>
	<td><input type="text" size="3" maxlength="3" name="endingx" value="<?php echo (isset($_POST['endingx']) ? $_POST['endingx'] : '')?>" /></td>
</tr>
<tr>
	<td>Enter initial y value, y(0):</td>
	<td><input type="text" size="3" maxlength="3" name="initialy" value="<?php echo (isset($_POST['initialy']) ? $_POST['initialy'] : '')?>" /></td>
</tr>
</table>

 

[BenGoldberg]

WOW I'm not sure why I forgot to try this. You would think it would work, and it does keep the values in the forms, which I wanted to do anyways. But I just tested it and as soon as I hit that second submit button it still wipes out all my old data. Now I really don't know why, but I guess I don't fully understand how the SELF POST method works. Any other ideas? And thank you btw for helping me with this, it's actually part of a school project that's due Thursday so it really is a big help.

[BenGoldberg]

Still have figured this out, and I only have one more day. Anyone?

[xyph]

Is it possible to use sessions to keep the data persistent between pages?

[cyberRobot]

If I understand the issue correctly, it sounds like you're having problems with losing data in the second form; the one that displays the drop-down menu. If that's the case, you need to create hidden variables for whatever you want to pass through the form. For example:

 

<input type="hidden" name="initialy" value="<?php echo $_POST['initialy']; ?>" />

 

 

Also, I would strongly recommend that you avoid using $_SERVER['PHP_SELF'] in your form action attribute. It's very easy to hack PHP_SELF when it's used in the action attribute, in links, or when it's displayed on screen.

http://www.mc2design.com/blog/php_self-safe-alternatives